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BIOL 253 Final Exam 2025: Cell Membrane Transport and Cardiac Electrophysiology, Exams of Biology

A comprehensive overview of cell membrane transport mechanisms, including diffusion, mediated transport, and epithelial transport. It delves into the intricacies of cardiac electrophysiology, covering the electrical pathway, action potentials in pacemaker and contractile cells, and excitation-contraction coupling. The document also explores the cardiac cycle, cardiac output, and the autonomic nervous system's role in regulating heart function. It is a valuable resource for students studying cell biology and physiology.

Typology: Exams

2024/2025

Available from 02/26/2025

LennieDavis
LennieDavis 🇺🇸

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BIOL 253 FINAL EXAM 2025 QUESTIONS AND
CORRECT ANSWERS
What do cell membranes consist of?
composed of phospholipid bilayer, proteins, cholesterol
What is the purpose of cholesterol?
contributes to fluidity of membrane
Define Diffusion
passive moment from high to low concentration
factors that influence the rate of diffusion through the membrane
1. difference in concentration
2. surface area
3. permeability (solubility of membrane)
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BIOL 253 FINAL EXAM 2025 QUESTIONS AND

CORRECT ANSWERS

What do cell membranes consist of?

composed of phospholipid bilayer, proteins, cholesterol

What is the purpose of cholesterol?

contributes to fluidity of membrane

Define Diffusion

passive moment from high to low concentration

factors that influence the rate of diffusion through the membrane

  1. difference in concentration
  2. surface area
  3. permeability (solubility of membrane)

what kinds of molecules pass through the membrane easily

nonpolar, small uncharged, hydrophobic

permeability includes...

solubility in membrane, temperature, membrane thickness

rate of diffusion

factors are proportional to each other (C x A x P)

can the permeability of the membrane be changed?

yes, temporarily by channels or permanently by leak channels

movement of ions...

is subject to diffusional and electrical forces

how does membrane potential change?

net movements of ions

SGLT transporter

secondary active transport; substance is moved against gradient using a secondary source of energy, usually a Na+ concentration gradient (lumen to cell)

EPITHELIAL TRANSPORT

working together!

transcellular transport

transport through both cell membranes

how does transcellular transport work

  1. primary active transport (ATP) ensures low intracellular Na+
  2. using Na+ gradient, secondary active transport moves glucose against its gradient
  3. now that glucose is high inside the cell, the facilitated diffusion gradient will eventually diffuse into the blood

apical membrane

faces fluid cavity (lumen), body surfaces

basolateral membrane

later surfaces face other epithelial cells; basal cells face connective tissue

tight junctions

barrier preventing proteins from moving into basolateral membrane; keeps fluid separate in each membrane

IONIC COMPOSITIONS OF FLUID

what determines the composition of intra and extracellular fluids?

transporters/leak channels (Na/K ATPase and PMCA)

the diffusion gradient/leak channels

how can you make Ek+ more negative?

increase intracellular or decrease extracellular K+, which will increase the chemical driving force and result in more charge separation

equilibrium potential for an ion is the membrane potential at which...

an equilibrium is achieved between its chemical diffusion and electrical attraction/repulsions

to know the equilibrium potential for a particular ion, you need....

the ion's charge sign and its concentration inside and outside the membrane

GHK equation

predicts membrane potential by combining each ion's concentration and permeability

what ways does the ATPase pump contribute to RMP...

gives asymmetry of ion concentrations, creating the membrane potential

can we temporarily change the membrane potential?

yes, by opening gated channels which increases permeability

why do ions move through the membrane?

the electrochemical driving force (the force at which a particular type of ion is driven through a channel)

electrochemical driving force

(mathematically) the equilibrium potential minus RMP (150mV)

CARDIAC ELECTROPHYSIOLOGY

electrical path

  1. SA node (pacemaker)

~internodal pathway~

  1. AV node

how are cells of the heart different?

fewer channels mean less action potentials

T-type Ca+ channels

helps further depolariation

L-type Ca+ channels

long lasting; much more permeable to Ca+. somewhat permeable to Na+

VG K+ channels

huge electrochemical driving force that pushes K+ out cell for repolarization

  1. cardiocytes (contractile cells)

plateau phase (atria and ventricles)

no net ion flux

leak channels and Na/K ATPase pump account for RMP as usual

Ca+ influx

L-type Ca+ channels open causing plateau

K+ efflux

K+ channels open and offset Ca+ influx

EXCITATION/CONTRACTION COUPLING

excitation-contraction coupling

connects action potentials and contraction (crossbridge cycle and generating tension)

skeletal muscle cell

  1. DHP Receptor: embedded in cell membrane, voltage sensor
  2. Ryanodine receptor: embedded in SR (ca+ channel)
  1. K+ and L-type channels open following depolarization
  2. Trigger Ca+ stimulates opening of RnR channels on SR to open
  3. Ca+ binds troponin, exposing myosin-binding sites
  4. actin-myosin interaction (contraction)

relaxation

  1. Ca+ is actively transported to ECF and SR by 3 types of transporters
  2. systolic Ca+ drops, and tropomyosin returns to cover myosin-binding sites

3 pumps for relaxation

  1. Ca+/Na+ antiporter (secondary)
  2. PMCA (primary active, pumps Ca+ out of cell)
  3. SERCA (primary active), pumps Ca+ from cytosol back into SR

what turns these pumps on to begin relaxation?

the availability of Ca+, turned on by contraction

REFRACTION/SUMMATION

cardiac muscle

the action potentials and tension occur over a much longer period of time

skeletal muscle

action potentials that are close in time can lead to summation of tension

what explains the comparatively long period of tension in cardiac muscle?

sustained release of Ca+ during the plateu phase

why is summation not possible in cardiac muscle cells? why would it harmful?

there is no ability to generate another AP until the refraction period. it would be harmful because there would be no time for ejection or filling

open before ejection and close after ejection

CARDIAC OUPUT

right side of heart

sends deoxygenated blood to the lungs and pulmonary capillaries

left side of heart

receives oxygenated blood from the lungs and pumps it to systemic capillaries and rest of the body

venous return

amount of blood returned to the heart (L/min)

cardiac output is calculated...

HR x SV

autonomic NS controls...

HR, SV, and conduction velocity

in response to...

reflex stimulation (baroreceptors, proprioceptors), higher brain activity (emotions)

hormones control...

HR, SV, and conduction velocity

in response to...

fight or flight response, need to elevate metabolism/temperature

ANS effect are:

  1. Chronotropic: affecting HR via SA node
  2. Ionotropic: affecting SV via contractile cells
  3. Dromotropic: affecting conduction velocity via conduction cells

Types of adrenergic receptors (bind to NE)

  1. Alpha or Beta receptors: GCPR receptors (a1, a2, b1, b2...)

b1 adrenergic receptors

responsible to positive chronotropic effects on sympathetic NS (through Gs system)

what does PKA do?

channel phosphorylation increases Ca+ permeability

what does cAMP do?

increases HCN permeability

big picture

sympathetic stimulation increases permeability of channels by second messenger system (GCPR)

role of hormones stimulated b

adrenal medulla releases epinephrine which binds to b1 receptor

thyroid hormones

T3 can pass through the cell to find an intracellular receptor (THR), which transcribes more b1 receptors

M2 receptor

responsible for negative chronotropic effects on parasympathetic NS

when ACh binds to M2...

alpha inhibatory subunit is released, inhibits adenylyl cyclase, cAMP gets cut off

remaining beta gamma binds to K+ leak channels (increasing permeability would slow pacemaker)