Download Ch 4 A Tour of the Cell 2016

A Tour of the Cell
Cell Structure
Chapter 4
The Fundamental Units of Life
All organisms are made of one or more cells
 The cell is the simplest collection of matter
that can be alive
 All cells are related by their descent from
earlier cells
 Though cells can differ substantially from one
another, they share common features

Biologists use microscopes and the tools of
biochemistry to study cells
Most cells are between 1 and 100 m in
diameter, too small to be seen by the unaided
eye-Scientists use Microscopes
 In a light microscope (LM), visible light is
passed through a specimen and then through
glass lenses
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LMs can magnify effectively to about 1,000 times
the size of the actual specimen
Lenses refract (bend) the light, so that the
image is magnified
Fluorescence
50 m
10 m
Light Microscopy (LM)
Confocal
Three important parameters of
microscope
1.
2.
3.
Magnification: the ratio of an object’s
image size to its real size
Resolution: the measure of the clarity of
the image, or the minimum distance
between two distinguishable points
Contrast: visible differences in parts of the
sample
0.1 m
Human height
Length of some
nerve and
muscle cells
Chicken egg
1 cm
100 m
10 m
1 m
100 nm
10 nm
1 nm
0.1 nm
Frog egg
Human egg
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
EM
1 mm
LM
1m
Unaided eye
10 m
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
Atoms
Superresolution
microscopy
Electron Microscopes

Electron microscopes (EMs) are used to study
subcellular structures
2 types of Electron Microscopes

1. Scanning electron microscopes (SEMs)
focus a beam of electrons onto the surface of a
specimen, providing images that look threedimensional
2 Types of Electron Microscopes
2. Transmission electron microscopes (TEMs)
focus a beam of electrons through a specimen
 TEM is used mainly to study the internal
structure of cells

Electron Microscopy (EM)
Longitudinal section
of cilium
Cross section
of cilium
Cilia
Scanning electron
microscopy (SEM)
2 m
Transmission electron
microscopy (TEM)
History of the
Microscope

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Invention & development of the microscope
enabled scientists to discover the cell
Simple Microscopes:
The microscope van Leeuwenhoek used is
considered a simple light microscope because it
contained one lens and used natural light to view
objects

Light Microscopes:
The microscope Hooke used to look at thin slices of
cork
Cell Discovery through
Microscopes
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Robert Hooke-the first to observe cells;built a
microscope and looked at cork cells from the bark of
a tree “coined the term cells” (1665)
Van Leeuwenhoek-observed the first living cells from
pond water-protists. He called them (animalcules) &
scraped tarter from his teeth
1838-Schleiden-botanist-all plants are made of cells
1839-Schwann-zoologists-all animals made of cells
10 yrs later-Virchow (1821-1902)-all cells come from
cells—Cell Theory
Cell Theory
1. All living organisms are composed of one or
more cells
2. Cells are the basic units of structure and
function in an organism
3. Cells come only from the reproduction of
existing cells
Comparing Prokaryotic and Eukaryotic Cells
The basic structural and functional unit of
every organism is one of two types of cells:
1. Prokaryotic Cells: Organisms of the domains
Bacteria and Archaea
2. Eukaryotic Cells: Protists, fungi, animals, and
plants

Comparing Prokaryotic and Eukaryotic Cells

Basic features of all cells
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Plasma membrane (phospholipids)
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)
Pili: (Fimbriae: attachment pili)
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
(a) A typical rod-shaped
bacterium
Cell wall
Capsule
Flagella
0.5 m
(b) A thin section through
the bacterium Bacillus
coagulans (TEM)
Prokaryotic cells are
characterized by having:
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No nucleus
DNA in an unbound region called the nucleoid
No membrane-bound organelles
Cytoplasm bound by the plasma membrane
Eukaryotic Cells
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Eukaryotic cells are characterized by having
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DNA in a nucleus that is bounded by a
membranous nuclear envelope
Membrane-bound organelles
Cytoplasm in the region between the plasma
membrane and nucleus
Eukaryotic cells are generally much larger than
prokaryotic cells
ENDOPLASMIC RETICULUM (ER)
Flagellum
Smooth ER
Rough ER
Nuclear
envelope
Nucleolus
NUCLEUS
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
Nuclear envelope
Nucleolus
Chromatin
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
NUCLEUS
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Cell wall
Wall of adjacent cell
Chloroplast
Plasmodesmata
CYTOSKELETON
In animal Cells but not plant
cells:
 1. Lysosomes
 2. Centrosomes with
centrioles
 3. Flagella (but present in
some plant reproductive
cells)
In plant cells but not animal
cells:
 1. Chloroplast
 2. Central Vacuole
 Cell Wall
 Plasmodesmata
3 Features All Cells have in
Common:
All cells have an outer boundary, inner
substance, and a control region:
1. Plasma membrane: the delicate skin of lipids
with embedded protein molecules
2. Nucleoid Region or Nucleus-the brain of the
cell
3. Cytoplasm: region within the plasma
membrane that is fluid based
1. Plasma Membrane
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Cells outer boundary
AKA Cell Membrane
Covers a cells surface and acts as a barrier
between the inside and outside of the cell
All material enter and exit through here

Phospholipid bilayer with globular proteins
embedded (proteins may be markers, transporters
or receptors)
2. Cytoplasm
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A semi-fluid matrix (gel-like) that contains
sugars, amino acids, and proteins; organelles
are suspended within it
The Cytosol is the part of the cytoplasm that
includes molecules and small particles like
ribosomes, but do not include membranebound organelle.
3. Nucleoid Region or Nucleus
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Control center; a membrane bound organelle
that contains a cell’s DNA
Center of the cell (usually); most prominent
structure
Most eukaryotes have a single nucleus, but
fungi and some other groups have many
nuclei.
Organelles
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Eukaryote cells have a variety of internal
membranes that divide the cell into
compartments called organelles or little organs
Well-defined, intracellular bodies that perform
specific functions for the cell
They carry out cellular processes
Bacteria Cell Walls
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Strong cell wall made of peptidoglycan, a
carbohydrate matrix (polymer of sugars)
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All bacteria is classified by into 2 types based
on their cell wall:
1. Gram-positive bacteria
2. Gram-negative bacteria
Gram Staining Procedures
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Gram-positive bacteria have a thick, single layered
cell wall that stains violet
Gram-negative bacteria have a multi-layered cell
layer and does not stain purple, but a pinkish red
See Notes
Bacterial Cell Wall Function
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Protect the cell
Maintain the cell’s shape
Prevents excessive uptake of water
Some bacterial cell walls are covered with a
polysaccharide-this helps the bacteria to stick
to substances like teeth, skin, and food
Some bacteria secrete a jellylike capsule
Bacterial Flagella
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Flagella are long threadlike structures that
protrude from the surface of a cell
They are used for locomotion & feeding
Bacteria swim by rotating their flagella (rotary
motor)
They are made of protein
Bacteria may have one flagellum or many
flagella (depends on the species)
Interior Organization of a Bacterial
Cell
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Cytoplasm (no support structures)
A few ribosomes (but no other membrane
bound organelles) make protein
Plasma (cell) membrane-controls what goes in
and out of bacterium
Nucleoid: area within cytoplasm where DNA
is located
Flagella: whip-like tail (with Rotary motor)
Pili: hairlike growths on the outside of the cell
Eukaryotic Cells
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More complex than prokaryotic cells
Many membrane organelles; functions
important for cell division
Made of tiny organelles/little organs
-Nucleus Region
- Cytoskeleton
-ER Region
-Centriole
- Lysosome
- Mitochondria
- Vacuole
- Golgi Apparatus
Cell Organelles and Features
Plasma membrane
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AKA: cell membrane; has several functions
Allows only certain molecules to enter or leave
the cell
It separates internal metabolic reactions from
external conditions & Allows the cell to
excrete waste & interact with its environment
Made of phospholipids with embedded
proteins
Nucleus “Control Center”
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Nucleus controls most of the functions in eukaryote
cells
Filled with a jellylike liquid called nucleoplasm holds
the contents in place
The nucleus is surrounded by a double membrane
called the nuclear envelope
Covering the surface of the nuclear envelope are tiny
protein-lined holes called nuclear pores. They provide
passageways for RNA and other materials to enter
and leave the nucleus
Nucleus “Control Center”
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The nucleolus is the site where DNA concentrated by
processing ribosomes
DNA in the form of thread-like materials is called
chromatin. Before the cell divides, chromatin changes
to chromosomes
Nucleus
Nucleolus
Chromatin
Nuclear envelope:
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Pore
complex
Ribosome
Close-up
of nuclear
envelope
Chromatin
Mitochondria

Transfer energy from organic molecules to
adenosine triphosphate (ATP)
High active cells (muscle cells) have hundreds of
mitochondria
 Low active cells (fat storage cells) have few
mitochondria
Mitochondria have their own DNA-contains genes
that make proteins needed for cellular respiration
Mitochondria can divide-but also involves nuclear
enzymes
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Parts of the Mitochondria
Double membrane:
1. Outer Membrane: separates the mitochondrion from
the cytosol
2. Inner Membrane: has many folds called cristae
Cristae contain proteins that carry out energyharvesting chemical reactions
 The matrix (fluid) is inside the inner membrane
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This is were cellular respiration occurs-glucose is metabolized into ATP
(energy molecules)
Ribosomes “Protein Makers”
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Where amino acids are assembled to make proteins
Has 2 subunits: a large and a small
Subunits are made of ribosomal RNA (rRNA) and
protein
The subunits are made in the nucleolus then move
through the nuclear pores to the cytoplasm
The subunits assemble when mRNA is present
(mRNA carries the DNA code)
Ribosomes on the ER make protein to be exported
Ribosomes in the cytoplasm make proteins to used
within the cell
Endoplasmic Reticulum “Highway”
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A system of membranous tubes and sacs called
cisternae (sis-TUHR-nee)
Functions as an intracellular highway or path
that molecules move from one part of the cell
to another
It is a Network of internal membranes made of
a lipid bilayer embedded with proteins
2 Types of ER
1. Rough ER: interconnected flattened sacs
covered with proteins; the ER transports
the newly made protein
Ex: Ribosomes on the rough ER make
digestive enzymes that accumulate inside
the ER.
Distributes Vesicles: little sacs that pinch
off from the ends & store them until they
are released from the cell
2 Types of ER
2. Smooth ER: lacks ribosomes; contain very
little smooth ER
contain enzymes involved in making carbs and
lipids
Ex: 1. In ovaries & testes: makes steroid hormones
estrogen and testosterone
2. In skeletal & heart muscle: releases calcium
3. Abundant in liver, kidney cells to help detoxify
drugs & poisons ( long-term use causes more
smooth ER)
Functions of Smooth ER
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The smooth ER
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Synthesizes lipids
Metabolizes carbohydrates
Detoxifies drugs and poisons
Stores calcium ions
Smooth ER
Rough
ER
Nuclear
envelope
ER lumen
Cisternae
Ribosomes
Transport vesicle
Transitional
ER
The Golgi Apparatus: Shipping and Receiving
Center
The Golgi apparatus consists of flattened
membranous sacs called cisternae
 Functions of the Golgi apparatus
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Modifies products of the ER
Manufactures certain macromolecules
Sorts and packages materials into transport
vesicles
Golgi Apparatus
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The sacs nearest the nucleus receive vesicles
from the ER containing newly made proteins
or lipids
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Vesicles travel from 1 part of the Golgi body to the
next transporting substances as they go
Proteins get “address labels” that direct them to
other parts of the cell
cis face
(“receiving” side of
Golgi apparatus)
Cisternae
trans face
(“shipping”
side of Golgi
apparatus)
Lysosomes “suicide sacs”
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Digestive vesicles
Arise from the Golgi
Contain enzymes that can digest carbs,
proteins, lipids and nucleic acids
Break down worn out organelles and recycle
molecules
In White Blood cells they phagocytize bacteria
Can merge with food vesicles and digest food
Other Vesicles
Enzyme-bearing, membrane-enclosed vesicles
 Found in the cells of plants, animals, fungi,
and protists
2 types:
1. glyoxysome: specialized peroxisomes;
found in seeds of some plant cells; contain
enzymes that convert fats to carbs.
2. peroxisomes: contain catalase enzymes,
which convert hydrogen peroxide into water
and oxygen; Similar to lysosomes
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Cytoskeleton
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Made of protein fibers that assemble and
disassemble
Support the shape of the cell
Anchor organelles to fixed locations
Functions based on 3 structural elements
1. Microtubules
2. Microfilaments
3. Intermediate Filaments
3 Types of Cytoskeleton
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Microtubules: Hollow tubes made of a protein
called tubulin which consist of 2 slightly
different subunits
Function:
1. holds organelles in place
2. maintain a cells shape
3. acts as tracks that guide organelles and
molecules as they move within the cell
3 Types of Cytoskeleton
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Microfilaments (Actin Filaments): long threads
of protein actin that are linked end to end &
wrapped around each other like two strands of
a rope
Function:
1. Contribute to cell movement (crawling, or
swim)
3 Types of Cytoskeleton
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Intermediate Filaments: are rods that anchor
the nucleus and other organelles to their places
in the cell
They maintain internal shape of the nucleus
Found in : hair-follicles (produce large
quantities which makes up most of the hair
shaft)
Cell Movement
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Cell Crawling:
Essential to inflammation, clotting, wound
healing, and spread of cancer
Cell Movement
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Cell Swimming: Flagella: Long, whip-like tail
(sperm)
In Eukaryotes: flagella (different from
prokaryotes
Cell Movement
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Cell Swimming: Cilia: Short, hair-like
projections
Organized in rows
Move mucus in
respiratory passage,
Move egg in
fallopian tube
Centrioles
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Barrel- shaped organelles in animals & protists
Occur in pairs: usually at right angles to one another
and situated in the cytoplasm near the nuclear
envelope
Usually near the nucleus
The region around them is called the centrisome
Some centrioles have DNA which makes structural
protein
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Centrioles help to organize microtubules and are found in
areas called microtubule-organizing centers Replicate and
move to opposite ends of the cell during mitosis (cell
division)
Plant Cells
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Have 3 additional structures that are important
to plant function
1. Cell Walls
2. Large Central Vacuoles
3. Plastids
Plants lifestyle Differ from
Animals
1.
2.
Plants make their own carbon-containing
molecules directly from carbon taken from
the environment
Plant cells take carbon dioxide gas from the
air and process it as photosynthesis (convert
carbon dioxide & water into sugars
Cell Wall
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A ridged layer that lies outside the cell’s
plasma membrane
Contain a carbohydrate called cellulose
Pores in the cell wall allow water, ions, and
some molecules to enter and exit the cell

Cell Walls: made of cellulose; protect and support
plant cell
Primary cell wall-laid down while cell is growing
Middle lamella-sticky substance that glues cells together
Secondary walls: are deposited inside the primary walls in
some plants
Central Vacuole
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Is a large, fluid filled organelle that stores
water, enzymes, metabolic waste, and other
materials
Forms as smaller vacuoles fuse together
Make up 90% of the plant cell’s volume & can
push all other organelles into a thin layer
against the plasma membrane
Other Vacuoles
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Other vacuoles store toxic materials
Ex: Acacia Trees store poisons that provide a
defense against plant-eating animals
Ex: Tobacco plant cells store the toxic nicotine
in a storage vacuole
Other vacuoles store plant pigments like the
pigment found in rose petals
Plastids
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Surrounded by a double membrane & have
their own DNA (like mitochondria)
Several types of plastids
1. Chloroplasts
2. Chromoplasts
3. Leucoplasts:
1. Chloroplasts “Photo
synthesizers”
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Carry out photosynthesis; manufacture own
food
Contain photosynthetic pigment chlorophyll
that gives most plants their green color
Double membrane
Have their own DNA
Bodies of Chloroplast
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Each chloroplast contains a system of flattened
membranous sacs called thylakoids; contain the
green pigment chlorophyll (absorbs light &
captures light energy for the cell)
The stroma is an area inside of the chloroplast
where reactions occur and starches (sugars) are
created; fluid matrix
One thylakoid stack is called a granum
Outer & inner membranes: lie close to each other
2. Chromoplasts
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Are plastids that contain colorful pigments that
may or may not take part in photosynthesis
Ex: carrot root cells contain chromoplasts
filled with orange pigment carotene
Chromoplasts in flower petal cells contain red,
purple, yellow or white pigments
Other Plastids
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Leucoplasts: starch (white) storage sites in root
cells and other plant cells
A leucoplast that stores starch is sometimes
called an amyloplast
Comparing Cells
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Plant Cell have a Cell Wall
Plant Cells contain a large central vacuole
Plant cells contain a variety of plastids