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Cell Biology Exam 2 SH


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Membrane Functions
Cell Communication
Import/Export of molecules

What makes up phospholipids and most abundant
Polar Head
Fatty acid tails


Phospholipid Bilayer
Assymetric (not same # on opposite sides)
Move by:
-Lateral Diffusion

Synthesize the bilayer

Move phospholipids to opposite side of bilayer with enzymes

Macrophages take away dying cells

Membrane Protein Functions
Transport nutrients
Anchor membrane to macromolecules
Receptors to detect signals
Work as enzymes to catalyze reactions

Hemotaxis-move toward chemical signals

How proteins move within the membrane
Cytoskeletal confinement
Directed motion
Transient confinement(spontaneous)
Random diffusion

How can proteins be removed from the bilayer
-remove integral proteins
Integral Proteins
Scan the lipid bilayer

-Glycophorin-RB cells (a-helix)
-Bacteriordopsin-proton pump
-Porin-nonselective channel

Peripheral Proteins
Removed by interupting protein/protein interactions

Cross bilayer by a-helix (20AA)
Hydopathy Index-determines how many AA needed to cross layer

Disrupt Protein/Bilayer interaction

SDS-Sodium Dodecyl Sulfate

Parts of Microscope
Light source

Image and its properties
2-D representation of a 3-D object

Contrast-object from background
Resolution-object from other objects

Types of Light Microscopy
Bright-field-outline of cell and nucleus

Phase Contrast-halo

Differential-interference-3-D image

Fluorescence Microscopy
Dyes that stain certain parts of cell

Epifluorescence-light source and sample image go through same lens

Confocal Microscopy
Looks inside the cell
-Blurred background

Scanning Electron Microscope
Gives 3-D image
Transmission Electron Microscope(TEM)
Looks at cell detail
2 Classes of cell membrane transport proteins
Transporter-transfer small molecules by changing shape (Active or Passive Transport)

Channels-tiny hydrophilic pores (Passive transport)

Channel regulation
Permeable dependent on SIZE and CHARGE

-if ion is small enough and carries right charge then it can pass through open channel

Transporter regulation
Permeable to molecules that fit into binding site

Transfers by conforming shape

Passive/Active Transport
Passive-moves WITH the concentration gradient
(Facilitated diffusion)

Active-moves against concentration gradient

Membrane Potential
difference in electrical charges on each side of membrane

Cytoplasmic side has (-) charge

Electrochemical Gradient
Net force driving a charged solute across the membrane

Determines direction of passive transport


Na=high EG
K=Low EG

Active Transporters (examples)
Na-K Pump-uses ATP to pump Na out of cell and K into cell (against gradient)
-also an enzyme-ATPase
-called "Na+K+ATPase"

Ca2+Pumps-keeps Ca concentration mostly outside cell
-ATP-driven Ca2+Pumps
-maintains free calcium concentration

Glucose Transport
1.Epithelial cells(lumen) transfer glucose across lining by "Glucose-Na+ Symport"
-Apical surface-contains symport
2.Basal surface has PASSIVE GLUCOSE UNIPORTS to release glucose down concentration gradient
-Tight Junctions keep transporters separate

How do ion channels differ
1.Ion Selectivity-type of ions
2.Gating-conditions that influence opening and closing
Gated Channels and Regulations
VoltageGated-controlled by membrane potential(charge)
-used in neurons

LigandGated-controlled by binding of a ligand on inside or outside of membrane

MechanicalGated(StressGated)-controlled by mechanical force
-hairs in ear canals

K+/Na+ Channels
Resting State(cytosolic face negative)-Na channel closed and K channel partly open

Depolarized State(cytosolic face positive)-Na channel open and K channel open

K+ Leak Channels
Negative charges on inside cell are regulated by K+ channels
-Opens when Na+ channels close

Resting Membrane Potential
flow of +/- ions across a membrane is balanced
Concentration Gradients
(Na, K, Ca, Cl-)
Na=12-fold difference
K=40-fold difference(inside)
Ca=free calcium is not good
Cl=35-fold difference

Nernst Potential
Ca2+ K+ Positive Negative
Graph about Resting Potential
Depolarized-MP is higher than resting potential

Repolarized-MP is falling closer to resting potential
(Na and Ca stop moving through membrane)

Hyperpolarization-MP is below resting potential

Receive, conduct, and transmit signals
-Stimulated by a signal-this signal changes membrane potential at that site
Parts-Cell body, Axon, Dendrites(nerve terminal)

Resting Nerve Terminal-Ca2+ channel is closed
Activated Nerve Terminal-Ca2+ channel opens and transmits chemical signal
Activated Nerve Terminal-TransmitterGated channel accepts neurotransmitters
Active Synapse-chemical signal is changed to electrical signal

Action Potential
Traveling wave of electrical impulse
Triggered by rapid change in membrane potential
1.Fastest communication in body
2.Ca, K, and Na are crucial
3.Action potential alterations result in arrhythmias or epilepsy

3 Channels involved in Action Potential
1.VoltageGated Na+ channels
2.VoltageGated K+ channels
3.K+ Leak Channels

VoltageGated Na+ channels
Open during depolarization to allow ions into cell
-Form into 3 conformations:

VoltageGated Ca2+ Channels
Convert electrical signals into chemical signals at nerve terminals
-transports neurotransmitter
TransmitterGated Channels
Convert chemical signals back into electrical signals in target cells
-Changes membrane potential
VoltageGated K+ Channels
In nerve axon-return membrane to resting potential after Na+
3 Stages food is broken down
1.Digestion-enzymatic breakdown of food(catabolism)
2.Glycolysis-converts glucose into 2 pyruvate, 2ATP, and NADH
3.Oxidative Breakdown in mitochondria-Acetyl CoA goes through Citric Acid cycle to produce water, CO2, and NADH

Glycolysis facts
ANAEROBIC process-Oxidation still occurs with NAD+ and NADH
-Occurs in cytosol
-Cleaves into 2 pyruvate molecules
-Synthesis of ATP(Phosphorylation)
-Energy is harvested in steps 6&7
-AlphaGlucose is used

Pyruvates location during glycolysis
Junction between Aerobic and Anaerobic metabolism
Allows ATP to form without Oxygen
-How pyruvate breaks down
-NAD+ is regenerated by either producing lactate, ethanol, or CO2 as waste

CoEnzyme-A Facts
Pyruvate is oxidized to form CoA, NADH, and CO2 by PYRUVATE DEHYDROGENASE COMPLEX

Fatty acids and sugars are also formed into Acetyl CoA in mitochondria

Citric Acid Cycle (Krebs or Tricarboxylic acid cycle)
8 Reactions
-Requires Oxygen to turn NADH into NAD+ so cycle can continue

Generates 3 NADH, FADH2, GTP, and CO2 waste

Precursors formed by Glycolysis/Citric Acid Cycle

Others: amino acids, fatty acids, lipids, and nucleotides

Sleeping Sickness
Trypanozome-cannot do electron transport so it eats Glucose in the bloodstream which takes all ATP (no energy)

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