AP Biology
Ch. 4 – Cells: The Working Units of Life
Originally prepared by Kim B. Foglia. Revised and adapted by Nhan A. Pham
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Types of cells
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Cell Size
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Why organelles? § Specialized structures
- specialized functions § Containers
- partition cell into compartments - create different local environments
(separate pH’s, or concentration of materials)
- distinct and incompatible functions § Membranes as sites for chemical reactions
- unique combinations of lipids and proteins
- embedded enzymes and reaction centers
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Cells gotta work to live! § What jobs do cells have to do?
1. make proteins - proteins control every cell function
2. make energy - for daily life - for growth
3. make more cells - growth - repair - renewal
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Cells functions 1. Building proteins
- read DNA instructions
- build proteins
- process proteins (folding, modifying, removing amino acids, adding other molecules…)
- address and transport proteins
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Building Proteins § Organelles involved - nucleus - ribosomes - endoplasmic reticulum
(ER) - Golgi apparatus - vesicles
nucleus ribosome ER Golgi apparatus vesicles
The Protein Assembly Line
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§ contains most of cell’s DNA § How about the rest? § Function
- protects DNA § Structure
- nuclear envelope - double membrane - membrane fused in spots
to create pores which allow large macromolecules to pass through
Nucleus
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DNA
Nucleus mRNA
nuclear membrane
small ribosomal
subunit
large ribosomal
subunit
cytoplasm
mRNA
nuclear pore
production of mRNA from DNA in nucleus
mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore
1
2
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Nucleolus § Function − ribosome production − build ribosome subunits from
rRNA and proteins − exit through nuclear pores to
cytoplasm and combine to form functional ribosomes
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small subunit
large subunit Ribosomes
§ Function - protein production
§ Structure - rRNA and protein - 2 subunits combine 0.08µm
Ribosomes Rough
ER
Smooth ER
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Types of Ribosomes § Free ribosomes
- suspended in cytosol - synthesize proteins that function in cytosol
§ Bound ribosomes - attached to endoplasmic
reticulum - synthesize proteins
for export or for membranes
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Endoplasmic Reticulum (ER) § “little net within the
cytoplasm” § Functions
- processes proteins - manufactures membranes - synthesis and hydrolysis
of many compounds § Structure
- membrane connected to nuclear envelope and extends throughout cell
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Types of ER
rough smooth
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Smooth ER functions § synthesis
- synthesize lipids (oils, phospholipids, steroids and sex hormones)
§ hydrolysis - hydrolyze glycogen into
glucose (in liver) - detoxify drugs and
poisons (alcohol and barbiturates) by adding OH groups, making them more soluble and easier to flush from the body
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Rough ER functions § produce proteins for export
out of cell - secretory proteins are
glycoproteins - packaged into transport
vesicles for export § produce membrane for the cell
- membrane buds off and goes to parts of cell that needs membrane
Which cells have lot of rough ER?
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Synthesizing proteins
cytoplasm
cisternal space
mRNA
ribosome
membrane of endoplasmic reticulum
polypeptide
signal sequence
ribosome
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Golgi Apparatus
transport vesicles
secretory vesicles
§ Structure - consists of flattened sacs
(cisternae) with a cis and trans side
§ Function - finishes, sorts, tags and
ships cell products - ships products in vesicles
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cis and trans
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Vesicle transport
vesicle budding from rough ER
fusion of vesicle with Golgi apparatus
migrating transport vesicle
protein
ribosome
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proteins
transport vesicle Golgi
apparatus
vesicle
smooth ER
rough ER
nuclear pore nucleus
ribosome
cell membrane protein secreted
cytoplasm
Making proteins
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DNA
RNA
ribosomes
endoplasmic reticulum
vesicle
Golgi apparatus
vesicle
protein on its way!
protein finished protein
Making Proteins
TO:
TO:
TO:
TO:
nucleus
Regents Biology
Secretory Pathway
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Lysosomes § Structure
- vesicles of hydrolytic digestive enzymes, made by rough ER
- contain 40 different types of hydrolytic enzymes
§ Function - like “stomachs” of the cell,
digests macromolecules (phagocytosis)
- like a “clean up crew” of the cell, recycles broken cell’s parts (autophagy)
only in animal cells
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white blood cells (macrophages) attack and destroy invaders by
digesting them in lysosomes
1974 Nobel prize: Christian de Duve Lysosomes discovery in 1960s
1960 | 1974
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Cellular digestion
§ Lysosomes fuse with food vacuoles
§ hydrolyze polymers digested into monomers
§ pass to cytosol to become nutrients of cell
§ lyso = breaking things apart § some = body
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Lysosomal enzymes § Optimum pH is 5 while pH of cytoplasm is 7.
§ How do lysosomes achieve this acidic environment? Proteins in lysosomal membrane pump H+ ions from the cytosol into lysosome.
§ Digestive enzymes are not very active if leaked into cytosol – a safety measure for the cell.
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When things go bad… § Defective digestive enzyme in lysosomes pick up
biomolecules but can’t digest them § Over time, fill up with undigested material and grow
larger and larger until disrupt cellular function Ex: Tay-Sachs disease – build up undigested fat in brain cells
Some lysosomal storage diseases… § Lipids (Gaucher’s disease) § Glycogen and other polysaccharides (Farber disease, Krabbe disease) § Proteins (Schindler’s disease)
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Sometimes cells need to die… § Some cells have to die for
proper development in an organism
§ Apoptosis (auto-destruct) process Ex: tadpole tail gets re-absorbed when it turns into a frog Ex: loss of webbing between your fingers during fetal development
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Syndactyly
15 weeks
6 weeks
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Cells gotta work to live! 1. make proteins - proteins control every cell function
2. make energy - for daily life - for growth
3. make more cells - growth - repair - renewal
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Making Energy § Cells must convert incoming energy to forms that
they can use for work - mitochondria:
from glucose to ATP - chloroplasts:
from sunlight to ATP (active energy) and carbohydrates (stored energy)
+
ATP
ATP
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Mitochondria & Chloroplasts § Both
- convert energy to forms that cells can use
- have double membranes - are semi-autonomous
organelles (have internal ribosomes, own DNA and enzymes)
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Mitochondria § Almost all eukaryotic cells have
mitochondria
§ There may be 1 very large mitochondrion or 100s to 1000s of individual mitochondria
§ Number of mitochondria is correlated with aerobic metabolic activity
§ more activity à more energy needed à more mitochondria (in nerve and muscle cells)
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Mitochondria § Structure
- double membranes – smooth outer membrane and highly folded inner membrane (cristae)
- fluid-filled space between 2 membranes
- internal fluid-filled space (mitochondrial matrix) with DNA, free ribosomes and enzymes
Why 2 membranes?
increase surface area for membrane-bound enzymes that synthesize ATP
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Chloroplasts § belong to a family of plant
organelles called plastids
1. Amyloplasts – store starch in roots and tubers
2. Chromoplasts – pigments in fruits
3. Chloroplasts – store chlorophyll and function in photosynthesis
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Chloroplasts
Why 2 membranes?
§ Structure - double membrane - internal fluid-filled space
(stroma), membranous sacs where ATP is made (thylakoids), stacks of thylakoids (grana)
- DNA, ribosomes and enzymes - semi-autonomous (move, change
shape and reproduce by pinching in two)
§ Function - generate ATP and synthesize
sugars via photosynthesis
increase surface area for membrane-bound enzymes that synthesize ATP
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Endosymbiosis Theory § Mitochondria and
chloroplasts were once free living bacteria engulfed by ancestral eukaryote
§ Endosymbiont – cell that lives within another cell (host) in a partnership that is a evolutionary advantage for both. One supplies energy the other supplies raw materials and protection.
Lynn Margulis U of M, Amherst
1981 | -
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Endosymbiosis Theory Evolution of eukaryotes
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Peroxisomes § the other digestive
enzyme sacs in both animals and plants
§ break down fatty acids into smaller molecules
§ detoxifies alcohol by transferring hydrogen from the poison to oxygen and produce hydrogen peroxide (H2O2) which in turns is broken down to water and oxygen by enzymes
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Food & Water Storage plant cells
central vacuole
contractile vacuole
food vacuoles
animal cells
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Vacuoles and Vesicles § Function - little “transfer ships” - food vacuoles
(phagocytosis, fuse with lysosomes)
- contractile vacuoles (in freshwater protists, pump excess H2O out of cell)
- central vacuoles (in many mature plant cells)
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Vacuoles in plants § Functions - storage - stockpiling proteins or
inorganic ions - depositing metabolic
byproducts - storing pigments - storing defensive
compounds against herbivores
- selective membrane - control what comes
in or goes out ���
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Cells gotta work to live! 1. make proteins - proteins control every cell function
2. make energy - for daily life - for growth
3. make more cells - growth - repair - renewal
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Cytoskeleton Function § Structural support - maintains shape of cell - provides anchorage for organelles - protein fibers (microfilaments,
intermediate filaments, microtubules) § motility - cell locomotion (cilia, flagella, etc.)
§ regulation - organizes structures and activities of
cell
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§ actin § microtubule § nuclei
Cytoskeleton
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Centrioles § Cell division - in animal cells, pair of centrioles
organize microtubules - spindle fibers guide chromosomes in mitosis