Download Biology 40S Unit 1

Biology 40S
Unit 1: Classifying and
Understanding Life
Developed by Trevor Boehm
Hutterian Interactive TV
Prairie Rose School Division
1
Major Topics in Unit 1
 Definition of Life
 Linnean system of classifying life
– The five kingdoms (Monera, Protista, Fungi,
Plantae, and Animalia)
– Prokaryotic (bacteria / archaea) and eukaryotic (fungi
/ animal / plant) cells
– Domains of life (bacteria / archaea / eukaryotic)
 Cell theory
– Components of cells and their functions
– Differences between plant, animal, and bacterial cells
 Structure of DNA
– Nucleotide bases
– DNA replication
 Life processes:
– Cellular respiration
– Cell division (mitosis) and the cell cycle
– Protein synthesis
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What is “Life”?
 What a silly question, right?
 I dare you to answer it without
using words like “alive” or
“living”.
 And no trying to explain it with
examples, either!
 Not so easy, eh?
3
Life Comes in All Shapes
and Sizes
 There are currently 2 million recognized species of
living organisms on earth… maybe a lot more.
 Some are so small they can’t be seen with a
microscope. Some are larger than a truck!
 Some live for hundreds of years. Some live for a
few hours.
 Some walk around. Some swim. Some fly. Some
don’t seem like they’re moving at all.
 All of the images on the left of this PowerPoint are
alive, and they look nothing alike!
 Obviously, we can’t use shape or size (what it looks
like) to tell if something is alive or not.
4
Characteristics of Life
All life shares the following basic
characteristics:
…is made up of cells.
…can reproduce.
…grows and develops over time.
…produces and uses energy.
…responds to changes in environment.
…moves (internal or external).
…passes genetic info on to next
generation.
…is highly organized.
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Many Living Organisms
 Having established what “being alive” looks
like, we have another problem… there’s a
lot of life on earth!
 Scientists have identified more than 2
million unique types of organisms on earth.
 It is estimated that 40 million species
inhabit the earth.
 There may be millions of types of living
organisms in the tropical rain forest and
oceans yet undiscovered. Every year,
thousands of new species are discovered.
 In order to make sense of all this life in our
world, we need a way to organize living
organisms into groups.
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The Purpose of Classifying
 There are two purposes to having a
classification system for living organisms:
– To assign a single, unique, and universal name
to each organism.
– To place organisms into groups that have real
biological meaning. That is to say, we want
organisms that are biologically similar to be in
the same group.
 A universal system is necessary to have clear
communication among scientists worldwide. We
can’t have scientists in Canada using one system
and scientists in Europe using a completely different
one. If that were the case, they wouldn’t be able to
easily cooperate or share their work.
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Taxonomy
 Taxonomy is the branch of
biology that deals with
classifying living organisms.
 There have been several
attempts through history to
develop an appropriate
classification system for living
organisms…
 …and scientists are still working
on it, as we will see.
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Aristotle’s Taxonomy
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Organisms were first classified more than
2,000 years ago by Greek philosopher
Aristotle.
He classified organisms as either plant or animal.
Animals were further divided into blood and bloodless. He
also divided animals into 3 groups according to how they
moved - walking, flying, or swimming (land, air, or water).
He grouped plants based on shape and stem, into categories
such as trees, shrubs, and herbs.
His system was used into the 1600s, but is no longer used
today.
Aristotle’s system made sense for his time, but as science
advanced, some problems appeared:
– There were problems using common names for organisms
• These names could vary based on country and language.
• Sometimes names were unclear (Malus meant apple, and Malus
Persica meant peach).
• Sometimes the names were long and cumbersome.
– Many new organisms were being discovered as the world was
explored by Europeans.
– In the late 1500s and early 1600s, scientists began developing
the first microscopes, and saw types of life Aristotle never 9
imagined.
Binomial Nomenclature
 The two-name system in common use today is
called the binomial system of nomenclature.
 Binomial = 2 names = genus and species.
 The first word of the name is the genus name, and
the second word is the species identifier. It is often
an adjective describing the organism, its geographic
location, or the person who discovered it.
 Using this system, the domestic dog is Canis
familiaris.
 Canis is the genus name for the group of animals
that includes dogs, wolves, coyotes, and jackals.
 The word familiaris acts as a descriptor to further
differentiate the domestic dog from its wild cousins.
 Every organism has its own name, and related
organisms are grouped together.
 This system is called the Linnean System, after
Carolus Linnaeus, the Swedish naturalist who
developed it in the mid-1700s.
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Genus and Species
 We still use the Linnean system of binomial
nomenclature today.
 Scientific name of an organism consists of its
genus and species (for example, the scientific
name of humans is Homo sapiens).
– A species is the smallest group of organisms which
can produce offspring capable of reproduction.
– A genus is a group of closely related, similar species.
 Latin is used because it is a dead language (does
not change) and can be used in many countries.
 When we use the Latin name for an organism, we
always capitalize the genus but not the species
Identifier. We also print the name in italics or
underline them.
 For example:
–
–
–
–
Acer rubrum is the red maple tree.
Acer is the Latin name for maple (genus)
rubrum is the Latin word for red (species)
The name can be abbreviated as A. rubrum.
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Seven Levels of
Classification
 Just a genus and species, however, doesn’t
make a classification system.
 Remember, today we have 2 million species
to classify, and we can expect to add many
more in the future.
 The Linnean System included seven levels of
grouping to organize similar organisms
together:
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Kingdom
Phylum (Division in the plant kingdom)
Class
Order
Family
Genus
Species
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King Phillip Cried Out…
Kingdom
Phylum / Division
Class
Order
Family
Genus
Species
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5 Kingdoms
 Linnaeus classified all organisms into two
kingdoms, plantae and animalia.
 Modern taxonomists recognizes that many
organisms are neither plant or animal.
 Today, we have 5 major kingdoms:
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Monera
Protista
Fungi
Animalia
Plantae
 Organisms are sorted into one of these 5
based on their characteristics.
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Five Kingdoms
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Linnean Classification of a
Human Being
 Kingdom: Animalia (with eukaryotic cells having
cell membrane but lacking cell wall, multicellular,
heterotrophic)
 Phylum: Chordata (all animals with a notochord)
 Class: Mammalia (vertebrate, hair, warm-blooded,
bears live young)
 Order: Primates (collar bone, eyes face forward,
grasping hands with fingers, two types of teeth:
incisors and molars)
 Family: Hominidae (upright posture, large brain, flat
face, hands and feet have different specializations)
 Genus: Homo (s-curved spine, "man")
 Species: Homo sapiens (high forehead, welldeveloped chin, skull bones thin)
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Characteristics Used to
Determine Kingdom
1. Prokaryotic or Eukaryotic
2. Autotrophic or Heterotrophic
3. Unicellular, Multicellular, or
Colonial
4. Motile or Sessile
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Prokaryotes vs. Eukaryotes
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Prokaryotes are the simplest cells
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–
–
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Eukaryotic cells are much more complex
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The prokaryotic cell is bounded by a cell membrane, but does not contain any internal
membrane-bound organelles.
Instead of a nucleus, it contains a region rich in DNA called a nucleoid.
Surrounding the nucleoid is a region of cytoplasm rich in ribosomes, small structures
which do the job of synthesizing proteins.
Finally, surrounding the plasma membrane is a cell wall
Prokaryotes can have surface appendages which do particular jobs. Flagella are used
for locomotion, for example.
Bacteria (monerans) are prokaryotes.
Prokaryotes can be either autotrophic or heterotrophic.
There are no multicellular prokaryotes.
Much of the cell is taken up by organelles bound by their own membranes
(mitochondrea, chloroplasts, nucleus, vacuoles, lysomes, etc.)
Eukaryotic cells have a nucleus which contains all of the cell's DNA.
Both cell types have many, many ribosomes, but the ribosomes of the eukaryotic cells
are larger and more complex than those of the prokaryotic cell.
Eukaryotic cells are larger than prokaryotes.
There are multicellular and unicellular eukaryotes.
Like prokaryotes, eukaryotes can also be either autotrophic or heterotrophic.
Protists, fungi, plants, and animals are all eukaryotes.
“Eukaryote” means “true nucleus” while “prokaryote” means “before the
nucleus”.
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Diagram of Eukaryotic and
Prokaryotic Cells
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Common Features of
Prokaryotes and Eukaryotes

The common features of prokaryotic and eukaryotic
cells are:
1. DNA, the genetic material contained in one or more
chromosomes and located in a nonmembrane bound
nucleoid region in prokaryotes and a membranebound nucleus in eukaryotes
2. Plasma membrane, which separates the cell from
the surrounding environment and functions as a
selective barrier for the import and export of materials
3. Cytoplasm, the rest of the material of the cell within
the plasma membrane, excluding the nucleoid region
or nucleus, that consists of a fluid portion called the
cytosol and the organelles and other particulates
suspended in it
4. Ribosomes, the organelles on which protein
synthesis takes place
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Diagram - Common Features of
Prokaryotes and Eukaryotes
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Autotrophic vs.
Heterotrophic
 These terms relate to how an organism gets its
food.
 Autotroph - organism that makes organic
compounds from inorganic sources. Plants, some
bacteria, and some protista make their own food
using light energy (photosynthesis). Some
organisms are also capable of synthesizing energy
chemically (chemosynthesis).
 Heterotroph - organism that cannot make organic
compounds from inorganic sources. They obtain
their organic compounds by consuming other
organisms. Almost all animals, fungi and some
Protista and bacteria.
 All food molecules come ultimately from autotrophs,
either directly or indirectly.
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Unicellular vs. Multicellular
vs. Colonial
 These terms refer to how many cells
an organism has.
 Unicellilar – one-celled. Bacteria
and most protists are unicellular, and
a few fungi are also unicellular.
 Multicellular – many-celled, with
different types of specialized cells.
All animals and plants and most
fungi are multicellular.
 Colonial – many-celled, but all
exactly the same type of cell. Some
protists (algae) are colonial.
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Sessile vs. Motile
 Whether the organism is
stationary (sessile) or capable of
self-propelled motion (motile).
 Fungi and plants are sessile.
 Bacteria, protists, and animals
are motile.
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Chart Showing Classification
into Kingdoms
Kingdom
Key Characteristics
Examples
Bacteria, blue-green algae
Monera
Prokaryotic
Unicellular
Autotrophic or heterotrophic
Sessile or motile
Protista
Eukaryotic
Unicellular or colonial
Autotrophic or heterotrophic
Sessile or motile
Ameba, paramecium,
euglena, algae
Eukaryotic
Mostly multicellular
Heterotrophic
Sessile
Mushrooms, molds &
mildews, yeast (unicellular)
Eukaryotic
Multicellular
Autotrophic
Sessile
Moss, ferns, flowering plants,
bushes, trees
Eukaryotic
Multicellular
Heterotrophic
Motile
Insects, jellyfish, hydra,
crabs, fish, birds, lions,
tigers, and bears (oh my!)
Fungi
Plantae
Animalia
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General Rules for
Classifying into Kingdoms

Yes, I know it looks like a lot to remember. Here
are a couple generalizations that may help you
keep some of that table straight:
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Only one kingdom has organisms that are
prokaryotic (the moneran kingdom).
For the most part, any organism that is unicellular
and eukaryotic is a protist (one exception is yeast, a
unicellular fungus) .
Fungi have the same characteristics as plants,
except that Fungi are heterotrophic and plants are
autotrophic, and their cell walls are different .
Animals are the only motile multicellular group.
Most of the autotrophic organism we study have
chlorophyll which gives them a greenish appearance.
So being "green" is an important clue --- it indicates
they are autotrophic (ex: blue-green algae, algae,
plants).
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Three Domains of Life
(To Complicate Matters)
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Starting in the early 1970s, scientists began to find evidence for
a previously unknown group of single-celled organisms.
These organisms lived in extreme environments - deep sea
hydrothermal vents, "black smokers", hot springs, the Dead Sea,
acid lakes, salt evaporation ponds - environments that scientists
had never suspected would contain much life (It was there all
along, we had just never thought to look for it!).
These unusual organisms were considered to be bacteria and
named archaebacteria ('ancient' bacteria). They did not need
sunlight or oxygen to grow, instead making all of their food from
hydrogen sulfide and other chemicals spewing from the volcanic
vents, living in a complex ecosystem with many other living
organisms near the warm, mineral-rich waters of the vents.
However, as scientists studied the archaebacteria, they found
that their DNA is more than 50% different from the DNA of the
Monera. To put this in perspective, archaea have more DNA in
common with eukaryotic organisms than they do with bacteria.
Based on this, scientists propose that there should be a new
category of classification of life - the Domain, a classification
category above Kingdom.
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Three Domain System
 All eukaryotes are members of
the domain eukarya.
 Prokaryotes are seperated into
two domains:
– Traditional bacteria are members
of the domain eubacteria.
– Archaea are members of the
domain archaea.
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Three Domains
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Three Domains
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About Archaea
 Archaea look like bacteria - that's why they were
classified as bacteria in the first place. The
unicellular organisms have the same sort of rod,
spiral, and marble-like shapes as bacteria.
 Archaea and bacteria share some DNA, so they
function similarly in some ways. But archaeans also
share DNA with eukaryotes, as well as having some
DNA that is completely unique.
 Archaea are known for their preferred living
conditions. They are often referred to as
“extremophiles”, or “extreme lovers”.
– Some of these organisms live in hot acidic
environments; they are referred to as
thermoacidophiles.
– Those living in salty environments are called
“halophiles”(halo=salt).
– Methanogens are archaea that produce methane.
Methonogens live in anaerobic conditions such as
mash bottoms, intestines and in underground rocks.
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Cell Theory
 Cell theory states:
– All living organisms are made up
of cells and the products of those
cells.
– All cells carry out their own life
functions.
– New cells come from other living
cells.
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Relative Size of Cells
33
General Characteristics
of Cells
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Cells are complex and highly organized
– They contain numerous internal structures Some have membrane
bound organelles while others do not.
Cells contain genetic instructions (DNA) and machinery to use it
– Genes are instructions for cells to create specific proteins
– All cells have ribosomes, which are used to make proteins
Cells acquire and utilize energy
Cells can perform a variety of chemical reactions
– Transform simple organic molecules into complex molecules
– Breakdown complex molecules to release energy
– Metabolism = all reactions performed by cells
Cells can engage in mechanical activities
– Cells can move
– Organelles can move
– Cells can respond to stimuli (chemotaxis - movement towards
chemicals, phototaxis - movement towards light, hormone responses,
touch responses)
Cells can regulate activities
– Cells control DNA synthesis and cell division
– Cells make specific proteins only when needed
Cells all contain the following structures:
– Plasma membrane - separates the cell from the external environment
– Cytoplasm - fluid-filled cell interior
– Nuclear material - genetic information stored as DNA
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Different Types of Cells
 Though all organisms are made up of cells,
they aren’t all made up of the same types
of cells.
 For our purposes, we’re going to examine
three major categories of cell:
– Bacteria
– Plant
– Animal
 The cells we’ll be examining are
generalized – they are a “typical” bacterial,
plant, and animal cell. In reality, there is a
lot of specialization for particular purposes.
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Features of Prokaryotic Cells
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Capsule - outer sticky protective layer
Cell Wall - rigid structure which helps the bacterium maintain
its shape
– this is not the same as the cell wall of a plant cell
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Plasma membrane - separates the cell from the
environment
Mesosome - infolding of plasma membrane to aid in
compartmentalization
Nucleoid - region where DNA is found loose within the cell
Cytoplasm
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semi-fluid cell interior
no membrane-bound organelles
location for metabolic enzymes
location of ribosomes for protein synthesis
Flagella (singular flagellum) - One or many threadlike motile
structures (locomotion)
Pili (singular, pilus) - small hairlike projections emerging from
the outside cell surface, assist bacteria in attaching to other
cells and surfaces, specialized pili are used for conjugation,
during which two bacteria exchange fragments of DNA.
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Prokaryote Cell Diagram
37
Features Common to Plant
and Animal Cells
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Plasma Membrane - All living cells have a plasma membrane that encloses their
contents. In prokaryotes and plants, the membrane is the inner layer of protection
surrounded by a rigid cell wall. These membranes also regulate the passage of
molecules in and out of the cells.
Nucleus - The nucleus is a highly specialized organelle that serves as the information
processing and administrative center of the cell. This organelle has two major
functions: it stores the cell's hereditary material, or DNA, and it coordinates the cell's
activities, which include growth, intermediary metabolism, protein synthesis, and
reproduction (cell division).
Endoplasmic Reticulum - The endoplasmic reticulum is a network of sacs that
manufactures, processes, and transports chemical compounds for use inside and
outside of the cell. It is connected to the double-layered nuclear envelope, providing a
pipeline between the nucleus and the cytoplasm. In plants, the endoplasmic reticulum
also connects between cells via the plasmodesmata.
Golgi Apparatus - The Golgi apparatus is the distribution and shipping department for
the cell's chemical products. It modifies proteins and fats built in the endoplasmic
reticulum and prepares them for export as outside of the cell.
Microfilaments - Microfilaments are solid rods made of proteins. These filaments are
an important part of the cytoskeleton.
Microtubules - These straight, hollow cylinders are found throughout the cytoplasm of
all eukaryotic cells and carry out a variety of functions, ranging from transport to
structural support.
Mitochondria - Mitochondria are oblong shaped organelles found in the cytoplasm of
all eukaryotic cells. They release stored chemical energy in a process called cellular
respiration.
Ribosomes - All living cells contain ribosomes, which may be found either along the
rough endoplasmic reticulum or floating loose in the cytoplasm.
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Unique Features of Animal
Cells
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Centrioles - Centrioles are self-replicating organelles
made up of nine bundles of microtubules and are found
only in animal cells. They appear to help in organizing cell
division, but aren't essential to the process.
Cilia and Flagella - For single-celled eukaryotes, cilia
and flagella are essential for the locomotion of individual
organisms. In multicellular organisms, cilia function to
move fluid or materials past an immobile cell as well as
moving a cell or group of cells.
Lysosomes - The main function of these microbodies is
digestion. Lysosomes break down cellular waste products
and debris from outside the cell into simple compounds,
which are transferred to the cytoplasm as new cellbuilding materials.
Vacuoles – Animal cells may have several small vacuoles
used for storage and transport of materials.
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Animal Cell Diagram
40
Another Animal Cell
Diagram
41
Unique Features of Plant
Cells
 Cell Wall - Like their prokaryotic ancestors, plant
cells have a rigid wall surrounding the plasma
membrane. It is a far more complex structure,
however, and serves a variety of functions, from
protecting the cell to regulating the life cycle of the
plant organism.
 Chloroplasts - The most important characteristic of
plants is their ability to photosynthesize, in effect, to
make their own food by converting light energy into
chemical energy. This process is carried out in
specialized organelles called chloroplasts.
 Plasmodesmata - Plasmodesmata are small tubes
that connect plant cells to each other, providing
living bridges between cells.
 Vacuole - Each plant cell has a large, single
vacuole that stores compounds, helps in plant
growth, and plays an important structural role for the
plant.
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Plant Cell Diagram
43
Another Plant Cell Diagram
44
What is DNA
and Why is it Important?
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DNA stands for deoxyribonucleic
acid.
DNA is found in all living
organisms, including most cells in
our bodies.
Specifically, whenever a cell has
a nucleus, it will have DNA.
Mitochondrea and chloroplasts
also have their own DNA.
DNA is organized into
chromosomes. Different
organisms have different numbers
of chromosomes – humans have
46.
DNA contains the instructions for
how an organism looks and acts –
the complete makeup of an
organism is stored within its DNA.
DNA is passed from parent
organism to child organism in a
process known as inheritance.
DNA is sometimes also called
“the genetic code” because
information is stored in DNA
molecules using a chemical code.
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Uniqueness of DNA
 Every organism’s DNA is unique,
except for identical twins.
 The DNA of similar organisms will be
similar, but not identical.
 DNA has been used by law
enforcement to identify blood and
hair as belonging to a particular
person. DNA evidence is now widely
accepted in courts.
 Scientists hope that by
understanding DNA, they may be
able to find cures to some inherited
diseases.
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A DNA Molecule
 DNA has a very
unique shape
called a “double
helix”… though
students tend to
think of it as a
spiral staircase.
 Unravelled, the
structure of DNA
looks like a ladder.
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Structure of DNA
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The two sides of the ladder are
made of sugar and phosphate
molecules. The sugar in DNA is
deoxyribose, which is where the
molecule gets its name.
The rungs of the ladder are the
most important because they give
the cell its information. Each rung
is made of two nucleotide bases
joined together.
There are four possible nucleotide
bases in DNA.
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These bases pair up to form the
rungs of the DNA molecule:
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adenine (A)
guanine (G)
cytosine (C)
thymine (T)
A always joins to T
C always joins to G
A base pair refers to either a pair
of A and T or a pair of G and C.
A nucleotide refers to one base
plus the phosphate and sugar it is
attached to.
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Diagram of DNA Molecule
49
Another Diagram of DNA
50
Molecular
Diagram of
DNA
51
Nucleotide
Bases
52
DNA Replication
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DNA is shaped as a double helix for a reason.
The double-stranded DNA molecule has the unique ability that it
can make exact copies of itself, or self-replicate. When more is
required by an organism (such as during reproduction or cell
growth) the hydrogen bonds between the nucleotide bases break
and the two single strands of DNA separate.
New nucleotide bases attach to the two original strands, forming
two identical copies.
This is known as replication.
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DNA Replication Diagram
54
Unwound DNA Strand
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Cellular Respiration
 Cellular respiration is the process by which
the chemical energy of "food" molecules is
released and partially captured in the form
of ATP.
 Carbohydrates, fats, and proteins can all
be used as fuels in cellular respiration, but
glucose is most commonly used as an
example to examine the reactions and
pathways involved.
 Cellular respiration takes place in the
mitochondrea of cells.
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Chemical Reaction for
Cellular Respiration
 Reactants: glucose (or another
food source), oxygen
 Products: carbon dioxide,
water, and energy in the form of
ATP.
 Reaction
Glucose
Oxygen
Carbon
dioxide
Water
Energy
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Adenosine Triphosphate
ENERGY
STORED HERE IS
USED FOR
CELLULAR
WORK
58
Goal of Cellular Respiration
= Production of ATP
 Cells carry out the cellular respiration
in order to produce ATP.
 ATP stands for adenosine
triphosphate.
 ATP is an energy carrier. Energy is
stored in an ATP molecule in the
third phosphate bond (called a highenergy bond).
 Every time you move a muscle,
think, breathe, replicate your DNA,
every time your heart beats - you
use ATP to do this work.
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ATP as an Energy Carrier
60
Steps in Cellular
Respiration
 We can divide cellular respiration
into three metabolic processes:
glycolysis, the Krebs cycle, and the
electron transport chain. Each of
these occurs in a specific region of
the cell.
– Glycolysis occurs in the cytosol.
– The Krebs cycle takes place in the
matrix of the mitochondria (eukaryotes)
or in the cytosol (prokaryotes)
– The electon transport chain is carried
out on the inner mitochondrial
membrane (eukaryotes) or along the
inner cell membrane (prokaryotes).
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Glycolysis
 In glycolysis, the 6-carbon sugar, glucose,
is broken down into two molecules of a 3carbon molecule called pyruvate.
 This change is accompanied by a net gain
of 2 ATP molecules and 2 NADH
molecules.
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Krebs Cycle


The Krebs cycle occurs in the mitochondrial matrix and
generates a pool of chemical energy (ATP, NADH, and
FADH2) from the oxidation of pyruvate, the end product of
glycolysis.
Pyruvate is transported into the mitochondria and loses
carbon dioxide to form acetyl-CoA, a 2-carbon molecule.
When acetyl-CoA is oxidized to carbon dioxide in the
Krebs cycle, chemical energy is released and captured in
the form of NADH, FADH2, and ATP.
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Electron Transport Chain
 Transfers energy from NADH and
FADH2 to ATP.
 As electrons are passed from one
compound to the next in the chain,
their energy is harvested and stored
by forming ATP.
 For each molecule of NADH which
puts its two electrons in,
approximately three molecules of
ATP are formed, and for each
molecule of FADH2, about two
molecules of ATP are formed.
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Total Energy Production

Glycolysis
–
–

Formation of Acetyl CoA
–

2 NADH (= 6 ATP)
Krebs Cycle
–
–
–

2 ATP
2 NADH (= 4 ATP, these are converted to ATP in the mitochondria
during cellular respiration)
6 NADH (= 18 ATP)
2 FADH2 (= 4 ATP)
2 ATP
Overall = 36 ATP (this varies somewhat from cell to cell)
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Overview Diagram of
Cellular Respiration
66
Another Overview
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Mitosis – Cell Division





Like many things, cells wear out and die.
Therefore it is essential that organisms be able to
produce new cells, both to replace those that die,
and for reproduction and growth.
Cell division occurs rapidly in living organisms. For
example, in an adult human, millions of cells
divide each second to maintain homeostasis.
If cells are created by other cells, how exactly
does this happen?
The answer is mitosis, the process by which a
cell:
1.
2.

Makes a complete copy of its DNA, and
Splits in half.
Mitosis is essential for the creation of new cells in
all organisms.
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Stages of Mitosis
 Mitosis consists of four stages:
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
 Immediately after the completion of
telophase, cytokenesis is initiated to end cell
division by literally separating the cell in two.
 When a cell is not undergoing mitosis, it is
said to be in interphase.
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Interphase





Before starting to divide,
a cell is at the interphase
stage.
Chromosomes are not
visible .
Just before the visible
stages of cell division
begin, DNA is replicated,
nuclear proteins are
synthesised, new
ribosomes are made and
mitochondria and
centrioles divide.
The proteins which later
make up the spindle are
also made, even though
the spindle does not yet
form.
As a lot of energy is used
in division, the
mitochondria show high
levels of activity at this
stage.
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Mitosis - Prophase
 The beginning of mitosis.
 Chromosomes, which
have just been duplicated,
become visible as they
condense.
 The spindles which will
move the chromosomes
to opposite ends of the
cell starts to form.
 In animal cells, the two
centrioles move toward
the opposite end of the
cell.
 The nuclear envelope and
nucleolus start to break
up.
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Mitosis - Metaphase
 Spindle
becomes fully
formed.
 Chromosomes
line up in the
centre of the
cell.
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Mitosis - Anaphase
 The chromosomes
are pulled apart
and move to
opposite ends of
the cell, along the
spindle.
 Each half of the
cell gets half of the
DNA, a complete
copy of the DNA in
the original cell.
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Mitosis Telophase
 Chromosomes at each
end of the cell group
together and two nuclei
begin to form.
 The chromosomes begin
to decondense again as
the cytoplasm splits in
two, forming two new
cells.
 At the end of telophase,
cytokenesis takes place
and we have two
separate cells.
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Summary of Mitosis

Prophase:
•
•
•
•

Chromosomes condense
Nuclear envelope disappears
Centrioles move to opposite sides of the cell
Spindle forms and attaches to centromeres
on the chromosomes
Metaphase
• Chromosomes lined up on equator of
spindle.
• Centrioles at opposite ends of cell.

Anaphase
• Chromosomes pulled to opposite poles by
the spindle

Telophase
• Chromosomes de-condense
• Nuclear envelopes reappear
• Cytokinesis: the cytoplasm is divided into 2
cells
75
Overall Diagram of Mitosis
76
Overall Diagram of Mitosis (2)
77
Mitosis in Plants
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The Cell Cycle






Cells that are growing
and dividing go through a
repeating series of
events called the cell
division cycle (or cell
cycle).
During the first phase
(G1), the cell grows and
prepares for DNA
replication.
DNA replication occurs in
the S phase.
Further growth takes
place in the G2 phase
Finally mitosis occurs in
the M phase.
Cells can exit the cell
cycle and cease division
either permanently or
temporarily, entering
what is known as the G0
phase.
79
Cell Cycle Diagram
80
Protein Synthesis
 Synthesis = putting together =
creation.
 Proteins are created from
individual amino acids.
 This takes place in the
ribosomes of cells, located
along the rough endoplasmic
reticulum and in the cytoplasm.
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How a Cell Knows What
Protein to Make and How
 The instructions for making all the proteins
needed by a cell are contained in the cell’s
DNA, in the nucleus of the cell.
 This poses two problems:
– DNA never leaves the nucleus (except for
mitosis), so we need a way to get the
information from the nucleus to the ribosomes.
– DNA is coded in nucleotide bases, proteins are
made up of amino acids. We need some way to
convert the DNA code into the proper series of
amino acids.
 Both of these problems are solved by RNA.
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RNA
Ribonucleic Acid
 Different from DNA in a few
key ways:
– The base Thymine is replaced
by Uracil.
– Uracil pairs with Adenine in
RNA
– Single strand instead of double
helix.
– Sugar is ribose instead of
deoxyribose.
 But it does the same job –
carries the series of
nucleotide bases that
comprise the genetic code.
 Two types: messenger RNA
(mRNA) and transfer RNA
(tRNA).
83
Molecules Present in
DNA vs. RNA
84
Protein Synthesis
Part 1 - Transcription
 Cell receives a message to make a
certain quantity of a protein.
 The portion of the DNA double helix
that contains the instructions for how
that protein is made unravels.
 RNA nucleotides (which are floating
around the cell) attach to one of the
exposed DNA strands and form a
molecule of messenger RNA.
 Multiple copies of messenger RNA
are made.
 These mRNA molecules leave the
nucleus and travel to the ribosomes
that will make the protein.
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Protein Synthesis
Part 2 - Translation










A molecule of mRNA binds with the ribosome so that the RNA can
be read (decoded).
The RNA is read in units of 3 nucleotide bases. A unit of 3 bases of
mRNA is called a codon.
Each codon stands for a particular amino acid. When the
ribosome reads a codon of RNA, the corresponding amino acid is
activated by an enzyme.
A transfer RNA molecule attaches to the amino acid and brings it to
the ribosome. Enzymes recognize unique features on every different
tRNA molecule and will only join the correct amino acid to the correct
tRNA.
The transfer RNA molecule has a series of three nucleotide bases at
one end and a binding site for the amino acid at the other.
The three nucleotide bases on the tRNA molecule will be the
opposite of the ones in the mRNA strand, and are therefore called
an anticodon.
The tRNA anticodon matches with mRNA codon to bring the amino
acid into the proper position. The ribosome goes on to the next
codon, and the next amino acid is brought into position.
The first tRNA molecule releases its amino acid, and a peptide bond
forms between the two amino acids.
This occurs until the ribosome reads a “stop codon” on the mRNA.
At that point, the protein is released, and the mRNA and tRNA break
down so their nucleotides can be reused.
86
Stop codons are UAA, UAG, and UGA.
Transfer RNA
87
Diagram of Protein
Synthesis
88
Another Diagram of
Protein Synthesis
89
Transcription and
Translation Review
 Transcription
– RNA is made from DNA.
– Occurs in the nucleus of the cell.
– Result is creation of a strand of messenger
RNA.
 Translation
– Proteins are made from the message on the
messenger RNA.
– Occurs at the ribosomes.
– Molecules of transfer RNA bring the individual
amino acids indicated to the ribosome, where
they are joined together.
– Result is creation of a protein.
– Messenger and transfer RNA are broken down
for re-use.
90
The Genetic Code
mRNA to Amino Acid
91
Review of Unit 1
At the end of the unit, you should be able to:
 Categorize organisms into one of the five
kingdoms based on basic characteristics.
 Differentiate between plant, animal, and
bacterial cells, and identify features of
these cells on a diagram.
 Describe the processes of protein
synthesis, cellular respiration, DNA
replication, and mitosis.
 Differentiate between
prokaryote/eukaryote, DNA/RNA,
transcription/translation,
heterotroph/autotroph, and
codon/anticodon (to name a few).
 Assemble a working model of a 1914
Model T automobile from spare parts in
your shop while blindfolded. (Okay, I was
kidding on that one, but you should be
able to do the rest…)
92