Bio1A Study Guide for Test 1
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Lecture 5 – The Cell
A. Module 13: Overview of the Cell
a. Robert Hooke in 1665 was the first to observe cells (Fig. 1)
b. Cell Theory:
i. All living things are made up of cells. The smallest living thing is a cell and cells
may make up multicellular organisms.
ii. Cells arise from preexisting cells.
c. General features
i. Plasma membrane – allows isolation of cell contents, regulation of materials into
and out of cells, interaction with other cells.
ii. DNA as genetic material.
iii. Cytoplasm – fluid portion in the cell.
iv. Organization and size permit homeostasis.
1. Cells are generally small to allow greater surface area to volume ratio
(Fig. 2, Tab 1)
2. Different shapes and sizes depending on function (Fig. 3)
d. Prokaryotes vs. Eukaryotes
i. Prokaryotes are small, lack organelles. They have cell walls, nucleoids,
ribosomes. Some have fimbriae, flagella, capsules. (Fig. 6)
ii. Eukaryotes are bigger, contain organelles, and are more complex (Fig. 7).
1. Cell fractionation (not fractionalization!) is used to separate organelles
and cell components. Involves centrifugation and separation of pellet
from supernatant (Fig. 8)
B. Module 14: Eukaryotic Organelles
a. Differences between plants and animals – plants have a cell wall, plastids, central
vacuole. Animals have centrioles.
b. Nucleus – “control center” (Fig. 3)
i. Holds DNA in form of chromatin (DNA + protein). Chromosomes are the DNA
part.
ii. Nucleolus is center for ribosome assembly.
iii. Nuclear envelope is a double membrane. Nuclear lamina is meshwork. Nuclear
pores allow RNA to exit.
c. Ribosomes – “protein making machine”
i. Made from RNA and proteins.
ii. Found in cytosol, nuclear envelope, and rough ER.
d. Endomembrane System (5.15)
i. Endoplasmic Reticulum – “manufacturing center”
1. Membranes form flattened tubes. Lumen is on inside.
2. Rough ER has ribosomes. Proteins made and translocated into the lumen.
3. Smooth ER has no ribosomes. Used for lipid and carbohydrate
metabolism and detoxification.
4. Buds vesicles to Golgi.
ii. Golgi Complex – “post office” (Fig. 4)
1. Sorts incoming proteins and lipids
2. Receives at cis and ships at trans end.
3. “Tags” or modifies some for destination
4. Packages them for final destination in vesicles.
iii. Lysosomes – “digestive system” (Fig. 5)
1. Contains hydrolytic enzymes at low pH.
2. Digests all classes of macromolecules. White blood cells phagocytose
other cells.
3. Tay-Sach’s disease is genetic and is caused by missing digestive enzyme.
The enzyme digests lipids. Lipids build up and kill cell. Death occurs in
children
iv. Vacuole – “storage and recycling plant” (Fig. 12)
1. Store water, food, salts, pigments, and wastes.
2. Like a large vesicle.
3. Some protists have contractile vacuole
4. Huge in plants=central vacuole
e. Mitochondria – “powerhouse”
i. Produce ATP from glucose
ii. Structure: double membrane, intermembrane space, cristae (folds), matrix that
has enzymes. (Fig. 6)
f. Chloroplasts – “solar power plant” (Fig. 8)
i. Family of plastids that produce and store food.
ii. Makes glucose using chlorophyll and carotenoids
iii. Has three membranes. Inner most makes up thylakoid. Grana are stacks of
thylakoids. Stroma is inside space. Thylakoid lumen is inside thylakoid. Enzymes
in both stroma and thylakoid lumen.
g. Peroxisomes – “detox center”. Metabolize small organic compounds. E.g. Hydrogen
peroxide and ethanol. (Fig. 10, 11)
C. Module 15: Cytoskeleton
a. Involved in support, movements, and cell division
b. Fibers
i. Microfilaments – made from actin monomers. Small and helixed. Involved in
structure and movements. E.g. muscle contraction, cytoplasmic movements (Fig.
2)
ii. Intermediate filaments – medium sized. Structural role. (Fig. 3)
iii. Microtubules – alpha and beta tubulin subunits wrapped in large helix. (Fig. 4)
1. Vesicle movement using motor proteins
2. Centrosomes – organizing center for cell division. Animal cells contain a
centriole
3. Cilia and Flagella – movement and water movement.
a. Cilia are small and numerous, “eyelash”
b. Flagella are large and few, “whip”
c. Uses microtubules connected by dynein arms. (Fig. 6).
Mechanism of movement is similar to motor protein movement
D. Module 16: Extracellular Components
a. Extracellular matrix is outside of membrane (Fig. 1)
b. Animal cell. (Fig. 2)
c. Junctions in animal cells (Fig. 2)
i. Tight junctions – “cement” – leak proof.
ii. Desmosome – “staple” – attaches adjacent cells
iii. Gap junctions – hole that allows messages through.
d. Plant cells have a cell wall. (Fig. 4)
i. Made from tough cellulose.
ii. Have plasmodesmata to allow communication (Fig. 5)
Lecture 6 – Membranes
A. Module 17: Membrane Structure
a. Fluid-Mosaic Model – Singer and Nicolson 1972 (Fig. 3)
i. Phospholipid bilayer is fluid (Fig. 1, 2)
1. Fluidity
a. Amphipathic phospholipids – polar head and nonpolar tails
b. Phospholipids move freely within its layer
2. Semipermeable to small nonpolar molecules only (water is exception)
3. Cholesterol helps stiffen membranes (Fig. 6)
ii. Proteins and carbohydrates give mosaic
1. Integral are embedded into hydrophobic part (Fig. 5) while peripheral are
only attached to a surface.
2. Variety of functions (Fig. 4). Transport, cell recognition, signaling, and
structure
b. Evidence of structure
i. Frye and Edidin 1970: different cells were labeled with different color tags.
Fusion of cells prove fluidity because colors blended (Fig. 7)
B. Module 18: Transport Across Membranes
a. Passive transport – diffusion is temperature dependent (Fig. 1)
i. Down a concentration gradient (high  low)
ii. Osmosis – diffusion of water across a membrane (Fig. 2)
iii. Tonicity – relation of solute concentrations across a membrane
1. Isotonic: =
2. Hypotonic < (in relation to cell)
3. Hypertonic > (in relation to cell)
4. These lead to certain conditions in plant and animal cells (Fig. 3)
a. Plant cells become turgid when in hypotonic solution and
plasmolysed when hypertonic solution.
b. Animal cells will lyse when in a hypotonic solution and crenate
when in a hypertonic solution.
iv. Proteins (e.g. carrier, channel protein) can allow solutes across that are too big to
cross lipid bilayer (Fig. 5).
1. Uniports transport one solute, antiports move two solutes in opposite
direction, symport same direction.
2. Aquaporins are channels for water. (Fig. 6)
b. Active transport
i. Against concentration gradient
ii. Requires energy
iii. Examples
1. Na-K pump – a bi-directional pump (Fig. 8)
a. Binding of Na allows ATP hydrolysis  conformation shift 
Na out.
b. K binding releases phosphate  shift  K in.
2. Electrogenic pumps create a charge gradient – e.g. proton pump (Fig. 10)
C. Module 19: Exocytosis and Endocytosis
a. Transport of large particles (bulk transport) uses vesicles (Fig. 1)
b. Exocytosis – particles are excreted.
c. Endocytosis – particles are taken in. (Fig. 4)
i. Phagocytosis – large particles are taken in – “cell eating”. Vacuole is formed
which may fuse with a lysosome.
ii. Pinocytosis – small particles are ingested – “cell drinking”.Vesicle then allows
contents to bleed into cytosol.
iii. Receptor-mediated endocytosis – uses a receptor for specific particle uptake. E.g.
LDL uptake
1. Receptors wait on surface. LDL binds.
2. Coat proteins bind and organize receptors. This causes endocytosis.
3. Vesicle forms and coat is removed.
4. Vesicle sent to lysosome. LDL released and receptors recycled.
iv. Disease, hypercholesterolemia, due to defective LDL receptors.
Lecture 7 – Cell Signaling
A. Module 20: Overview
a. Mating types of yeast (a and ) lead to early cell communication studies. Mating factors
are specific for mating receptors of opposite mating types. Binding causes shmoos
(mating projections)
b. Types of signaling depends on range/speed
i. Contact – cells must touch. Direct
ii. Paracrine – short distance with neighboring cells using chemical signals.
iii. Neuronal – long/short distances using electrical/chemical signals.
iv. Endocrine – long distance, uses hormones
c. Stages of cell signaling (Fig. 3)
i. Reception – signal is received. Binding of signal to receptor and information
transmitted to inside of cell. (Fig. 1)
ii. Transduction – relays and amplifies signal
iii. Response – a cellular response. Can be enzyme activity, gene activation, etc.
B. Reception – receives stimulus from a ligand binding a receptor.
a. Intracellular receptors
i. Loose in cytosol, e.g. steroid hormone receptors (Fig. 2)
ii. When bound, the complex travels to nucleus and initiates gene activity.
b. Ion channel receptors
i. Membrane bound. A signal opens a channel and ion flux initiates response (Fig.
5)
c. Tyrosine kinase receptors (Fig. 6)
i. Used by growth factors.
ii. Steps
1. Signal binds receptor monomers.
2. Receptors dimerize.
3. Tyrosines autophosphorylate
4. Relay proteins bind P-tyr and get activated
d. G-protein coupled receptors (Fig. 7)
i. Oldest and largest family. A “7 span” intermembrane protein
ii. G protein has three subunits: . Complex is membrane bound.
iii. When inactive, all three are bound, with GDP.
iv. Steps
1. Signal binds receptor
2. Full G protein binds receptor.
3. GDP is released from alpha and GTP replaces it.
4. Alpha releases beta/gamma and both are active. Each active parts bind
relay proteins.
5. Hydrolysis of GTP inactivates alpha and it binds back to beta-gamma.
C. Module 21: Signal Transduction Pathways
a. Goals
i. Links reception and response
ii. Amplification – signal increases in strength (Fig. 4)
iii. Divergence – signal can split off
iv. Convergence – signals can merge
b. Phosphorylation
i. A kinase is the enzyme that phosphorylates, phosphatase dephosphorylates
ii. Reaction involves transfer of phosphate. Often uses ATP as source (Fig. 1a)
iii. Usually causes a significant change of shape of a protein (Fig. 1b)
iv. A cascade is a series of phosphorylations
c. Second messengers
i. cAMP
1. Adenylyl cyclase converts ATP to cAMP (Fig. 2a)
2. cAMP activates PKA which begins a phosphorylation cascade
ii. IP3 and Ca-calmodulin (Fig. 3)
1. IP3 is formed by phospholipase C
2. IP3 signals calcium release from organelles by a channel.
3. Ca can directly activate pathways or bind calmodulin in other pathways.
Ca is loaded into certain organelles
D. Response
a. Two main responses
i. Enzymatic response – E.g. epinephrine signals glycogen breakdown in liver (Fig.
4). Also, formin formation in shmooing.
ii. Gene activation – E.g. growth hormones activate specific cell division genes.
(Fig. 8)
b. Regulation
i. Specificity is combinatorial
1. Pathways can converge or diverge to give unique responses. (Fig. 7)
2. Signaling “networks” are more the reality (Fig. 5)