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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

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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