Download Chapter 15: The Cell - Heritage Christian School

Chapter 15. The Cell
Cell Theory
• All living things are made up of one or more cells.
• The cell is the functional unit of life.
• All living things come from pre-existing cells
(Living from living vs. Spontaneous Generation)
What does “The Functional Unit of Life” mean? It is the smallest entity that
can carry out life functions.
GRIMNER…whether a human or a single cell…we all do it!
• Growth – the increase in size and/or development of new
structures.
• Respiration – the exchange of gases with the outside
environment.
• Irritability – the ability to respond to an external stimulus.
• Movement – either intra-cellular, intercellular, or within the
external environment.
• Nutrition – the assimilation and processing of energy sources
for growth and metabolism
• Excretion – the collection and removal of metabolic waste to
the external environment
• Reproduction – either by asexual or sexual means., to give
rise to new cells or new individuals.
All organisms haves specialized structures for fulfilling
specialized tasks.
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Generalized Cell Structure
Cell membrane – a thin, flexible outer covering, which acts as:
• An outer boundary to contain the cell
• A ‘gate-keeper” allowing for the selective transfer of gases,
nutrients and bio-molecules both in and out.
Nucleus – a large central structure surrounded by a nuclear
membrane. The nuclear membrane has a similar function to the cell
membrane. The nucleus contains the genetic material
(genes/chromosomes) responsible for the control of cell machinery.
The chromosomes are sometimes referred to as ‘chromatin’.
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Cytoplasm – a semi-liquid material located between the the cell
membrane and the nuclear membrane. This is where most of the
chemical reactions of the cell take place.
Organelles – specialized structures floating in the cytoplasm, each
having a specialized job to do.
• Vacuole – an organelle used for storage
• Mitochondria – the powerhouse of the cell – where cellular
respiration takes place.
• Ribosomes – reads mRNA and produces protein from the
instructions.
• Endoplasmic reticulum – tubes that collect protein made by
ribosomes and transports it around the cell.
• Golgi body – refines molecules made by cell for transport out of
cell.
• Centriole – part of the machinery used to divide the cell.
• Lysosome – breaks down (digests) food vesicles in the
cytoplasm.
Special PLANT Structures:
Chloroplasts – cellular organelles which collect light and produce
glucose through photosynthesis.
Cell wall – a tough outer coating made of cellulose, which acts like a
skeleton to help give cells form and rigidity.
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Large Central Vacuole – in plants the largest organelle is this
structure that can take up to 80% or more of the cell volume. It has
many functions:
• Storage facility for waste products,
• Water storage,
• Helps give rigidity (via hydrostatic turgor pressure)
Turgor
p. 340 Review 15.1
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Cellular Transport: Moving materials in and out
In plants the tough cellulose cell wall is really full of holes and will
allow almost anything in and out. The cell membrane however, is a
very complex structure made of lipids and specialized proteins. The
membrane is thin and flexible but is selectively permeable – that is it
will allow some things like water, oxygen and carbon dioxide to come
and go freely, but blocks others. Those that are blocked must enter
by way of these special carrier proteins, which are imbedded in the
membrane.
Types of Movement
Diffusion – the movement of molecules from an area of high
concentration to an area of low concentration (essentially, just
spreading out)
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Osmosis – this is a special type of diffusion; diffusion of water.
Question:
How can there be a ‘low concentration of water”?
Answer:
By having a higher concentration of solutes (stuff) dissolved in
the water.
Confused? Okay, think of it this way…water will move from an area
of purer water to an area of not-so-pure water.
***In cells the proportion of solutes in water must be maintained
at just the right level…otherwise there could be real trouble!
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Problem 1: Given a sea creature living in a tiny, inter-tidal pool. The
solute balance (concentration) between the outside water and the
inside cells must be kept the same. What would happen if there was
a sudden rain shower and the pool filled up with fresh water?
• First, what happened to the salt concentration in the pool? [↓]
• Second, what would happen to the water in the cells in the sea
creature? [osmosis out]
• Third, (bonus question) what do you think the sea creature
does to cure the problem? [increases solute level inside
cell…water osmosis back]
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Problem 2: Given a healthy plant with proper water balance.
Suppose no water fell for a couple of days, and the ground dried up
around the roots.
• First, what happens to the water concentration outside the
cells? [↓]
• Second, what would happen to the water inside the cell? [↓]
• Third, (bonus question) what do you think the plant cell does to
relieve the problem? [balances with stored water in vacuole...at
least until it runs out]
Review 15.2
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Cellular Energy
Photosynthesis – the production of energy “food” by plant and some
algae. Chloroplasts in plant cytoplasm contain chlorophyll which trap
light energy and use it to produce glucose and oxygen. The glucose
can then be:
• Used to run plant machinery
•
Stored as cellulose, starch or other sugars.
Carbon dioxide + water + light energy → glucose (chemical energy/food) + oxygen
CO2 + H2O + ην → C6H12O6 + O2
Cellular Respiration – when plants or animals use energy/food in the
cells. Respiration is the reverse process to Photosynthesis.
Glucose + oxygen → carbon dioxide + water + energy
C6H12O6 + O2 → CO2 + H2O + energy
***Since animals cannot make their own energy source, they must
eat, process the food to C6H12O6 , and then use it. Cellular respiration
takes place in the mitochondria.
Review 15.3
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A comment on the CO2/O2 Cycle. Carbon dioxide is constantly being
reconverted to oxygen and sugar by plants and algae. Both items are
necessary for life by all organisms: everything depends on plants to
keep this cycle going.
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Controlling the Machinery.
Cell activity can be summarized in two words:
Chemical Reactions.
Catalysts are Control Freaks! To control cell activity means to control
reactions. The rate at which reactions take place depends on whether
an enzyme catalyst is present or not. Cellular chemical reactions are
governed by catalysts!
Enzyme catalysts
• a protein that speeds up or slows down the rate of a chemical
reaction, but which itself does not enter into the chemical
reaction.
• enzymes are very specific: there is only one type of catalyst for
every type of reaction.
Therefore, if you can control how many and which types of catalysts
are available, then you can control the reactions.
How do they do that?
In a nutshell: By controlling the amount of catalyst (protein) made…by
controlling Protein Synthesis.
Protein Synthesis is probably the most important cell activity and it
controls everything about a cell, and an organism. It is referred to as
“The Central Dogma”
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In order to understand this important event we must first refresh our
memories on a bit of background information.
Nucleus –
• a large dark organelle normally located near the center of the
cell. It is the ‘brains of the cell” because it contains all the
plans for enzyme production which controls the life and
characteristics of the cell.
Nuclear membrane –
• the thin flexible membrane which surrounds th e nucleus and is
responsible for the control of passage of materials between
the cytoplasm and the nucleus.
DNA – Deoxyribo – Nucleic Acid .
• HUUUGE macro-molecules arranged in long strings which
make up (are) the genetic material of the organism.
Chromosome –
• a single, complete DNA molecule.
Gene –
• an area of a chromosome which contains the plans for a
single protein.
Okay, some pictures to explain:
• As you can see, the gene (plans) to make a protein catalyst are
located on a long strand of DNA (a.k.a. chromosome) and are
stored in the nucleus.
• At some point the DNA unravels so a copy/message (a.k.a.
mRNA) can be made.
• The mRNA travels through the nuclear envelope (nuclear
membrane) into the cytoplasm where the plans are decoded
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and a protein is made. The amount of catalyst made is
determined by how many copies of mRNA are made…this is
the control.
Pretty cool, eh!
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The Bible Analogy.
The Bible is like the nucleus: it contains all the instructions for life.
The books of the bible are like individual chromosomes: there are
many of them, each one contains huge storehouses of information,
but are divided into groups.
The chapters of each book are like genes: every chromosome is like
a beaded necklace of genes in a special order, every chapter must be
in it’s sequential order.
The words in each chapter are like the three base pair sequence: the
words ‘code’ for a certain meaning, the three base pair sequence
‘code’ for a certain amino acid, sort of like 3-letter words. (amino
acids make up proteins).
Each word in the bible is made up of combinations of 26 letters from
the English alphabet: each base pair sequence is made up of three
letters from an ‘alphabet’ of four…but together make up 20 words or
amino acids. It is the SEQUENCE that gives meaning to words and it
is the SEQUENCE that gives meaning to DNA, genes and
chromosomes.
Review 15.4
Single Celled Organisms (well sort of)
Protists
• have a nucleus and various organelles (i.e. membrane bound
structures).
• usually single celled (except some algae and seaweeds)
• some beneficial (e.g. algae are photosynthetic and contribute
greatly to the world’s production of oxygen)
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• some detrimental (e.g. produce disease (Amoeba - dysentry,
Plasmodium – malaria)
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Bacteria
• smallest and simplest forms of life
• always single – celled
• <0.002 mm long
• no nuclei
• usually no organelles
• single large circular strand of DNA (i.e. circular chromosome)
containing essential information
• sometimes has plasmids – small, non-essential circular DNA
• beneficial – some decomposers, some photosynthetic – O2
producers, some used in some food production – in
fermentation processes.
• detrimental – bacterial diseases
Bacterial Diseases and the Immune System
Pathogen – any disease-causing agent entering the body. Includes:
• poisons
• protests
• bacteria
• viruses
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How it works:
1. pathogen enters body.
2. body produces antibodies that attach to antigens located on
surface of pathogen cell wall. ⇒ slow response
3. pathogen becomes isolated and slows down so other ‘bacteriakillers’ (sort of like Pac-men) can destroy pathogen
4. immune system stores some of these new antibodies until next
time the pathogen gets into body. ⇒rapid response
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How Vaccines Work:
1. attenuated (dead or very weak) pathogens are injected into the
body.
2. body (immune system) responds by producing antibodies
3. defenseless pathogen is ‘killed’
4. antibodies are saved for next time pathogen (real infection)
enters body.
Essentially the immune system responds normally to a false alarm,
but remembers what the bad guy looks like so next time an invader
shows up it will be instantly recognized and quickly removed.
Viruses
•
•
•
•
•
~ 0.000 02 mm long
Cannot move by themselves
Non-living
NOT a cell – no cell components
Protein encased DNA strand. DNA code says, “MAKE
VIRUSES”
• Sometimes they have an additional protective coat and surface
spikes to help them stick to and enter poor unsuspecting cells
• Viruses are NOT ALIVE. They do not function until they get
inside another living organism and hijack the cell
machinery…very scarey!
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•
Employs ‘Trojan Horse’ warfare:
1. viruses enter a host cell and hijack enzymes and DNA to
reproduce thousands of copies of itself
2. produces sick cells ⇒ sick organism
3. cell bursts because of so many newly made viruses
4. spreads to other cells and repeats warfare.
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The Lytic Cycle
The Lysogenic Cycle
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Some Viral Diseases of Humans
• List 3 + AIDS from Table 15.1
Review 15.5
Read Article on STDs and summarize.
Activity 15E Cell Size and Surface area – why cells can’t get too big!
Review 15.6
Chapter Review.
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