Bio Exam 3 Flashcards

Phospholipids form a

liquid bilayer, which is like a “lake: in which some proteins float

What is the liquid mosaic model

The fluid mosaic model describes the structure of the cell membrane. It states that the membrane is composed of a fluid lipid bilayer with embedded proteins. The lipids can move laterally within the membrane, giving it a fluid nature. The proteins are scattered throughout, creating a mosaic pattern.

definition of mosaic

made of many discrete components

definition of fluid

components can move freely

Membranes are dynamic, meaning

they are constantly forming, transforming, fusing and breaking down

The cell membrane is selectively

permeable

membrane fluidity depends on factors such as,

liquid composition, lipid composition, and temperature

Membrane fluidity is associated with

permeability

Biological membranes are composed of

phospholipids and proteins

Integral membrane proteins are

at least partially embedded in the bilayer

Transmembrane Proteins

some integral proteins are transmembrane proteins, which extend all the way through the phospholipid bilayer

Anchored membrane proteins

covalently attached to fatty acids or other lipids inside the membrane

Peripheral membrane proteins

lack exposed hydrophobic regions, are noncovalently attached to the membrane and do not penetrate the bilayer

Top Hat Question: In a eukaryotic cell, a vesicle carried a protein to the cell membrane where it was inserted into the phospholipid bilayer. The vesicle budded off from the ___ before being inserted into the cell membrane.

a

cis-Golgi

b

Rough ER

c

medial-Golgi

d

Smooth ER

e

trans-Golgi

trans-Golgi

Protein or lipid components of membranes can be modified to have ______ added to them

carbohydrates

Top Hat question: Which of these proteins is most likely to be synthesized in the rough ER? Select all that apply.

a

Insulin a peptide hormone that travels in the bloodstream

b

β-adrenergic receptor which sits in the membrane of heart cells and signals to the cell to contract when bound to extracellular epinephrine

c

Dynein a motor protein that facilitates movement of cilia

d

Actin a component of the actin cytoskeleton

e

Lipase an acid hydrolase enzyme that uses water to break down fat molecules

• a

  Insulin a peptide hormone that travels in the bloodstream

• b

  β-adrenergic receptor which sits in the membrane of heart cells and signals to the cell to contract when bound to extracellular epinephrine

• e

  Lipase an acid hydrolase enzyme that uses water to break down fat molecules

Cell recognition

one cell specifically recognizes and binds to another cell of a certain type

Cell adhesion

the connection between the two cells is stregthened

What involves proteins and carbohydrates at the cell surface

Cell recognition and cell adhesion

What are the two types of cell adhesion

Homotypic: the same molecule sticks out from both cells and bind to each other

Heterotypic: the calls have different proteins that bind together

What are cell junctions

specialized structures comprised of many different proteins that hold cells together

What are tight junctions

a tight seal between cells, ensure directional movement of materials

What are gap junctions

form tunnels so that adjacent cells can communicate by exchanging small molecules, and electrical impulses

What are desmosomes

hold cells together and also allow materials to move around in the intercellular space

What is the ECM

the extracellular matrix - a macromolecule-rich gel outside of cells

What are integrins

one type of adhesion receptor that can facilitate movement by binding and reattaching to the extracellular matrix

The cell membrane is selectively ______

permeable

What is diffusion

the process of random movement of a solute from a region of higher concentration to a region of lower concentration

When particles are evenly distributed, they are at ______

equilibrium

Top Hat: The components of a biological membrane that allow it to have fluidity are...

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a

integral membrane proteins

b

carbohydrates

c

oligosaccharides

d

peripheral membrane proteins

e

lipids

lipids

Top Hat: A portion of the primary structure of an integral membrane protein is shown here. Which amino acids are most likely to comprise the transmembrane domain?

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a

#1-2

b

#3-17

c

#18-19

d

#1-19

e

Other

#3-17

Top Hat: types of membrane proteins

Review

Which membrane protein type would likely be removed most easily from a cell membrane in a laboratory experiment?

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a

Integral

b

Anchored

c

Transmembrane

d

Peripheral

peripheral

Top Hat: cardiomyocytes

Review

Heart muscle cells beat in unison because of the rapid spread of electrical current through…

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a

tight junctions

b

desmosomes

c

gap junctions

d

peripheral membrane proteins

e

neurons

gap junctions

What is concentration

the number of particles in a given volume

What type of substances can cross membranes by diffusion

Liquid-soluble (hydrophobic) substances

Membranes move across a permeable membrane until concentration is ____

equal on both sides

Energy for passive transport comes from the _______

concentration gradient

The rate at which substances diffuse in a solution depends on which factors

Size and mass, temperature, density of the solution, concentration gradient in the system, area across which a substance diffuses and the distance it diffuses

Water diffuses across a membrane in a process called

osmosis

Isotonic

equal solute concentration inside and outside the cell

Hypotonic

lower solute concentration outside the cell

Hypertonic

higher solute concentration outside the cell

Passive Transport

does not require energy input and transports substances down a concentration gradient

In a cell water moves across the membrane through channel proteins called ____

aquaporins

What are ion channels?

integral membrane proteins that have hydrophilic pores

• most are gated can be open or closed to ion diffusion

• The gate opens when the protein is stimulated to change conformation

• change in shape can be stimulated by the binding of a chemical signal (ligand)

What are carrier proteins

transport polar molecules, such as glucose, across membranes in both directions

Active transport

requires energy to move substances against a concentration and/or electrical gradient

The energy for active transport comes from

ATP hydrolysis, which releases energy

Active transport involves three proteins. What are they?

Uniporter: moves on substance in one direction

Symporter: moves two substances in one direction
Antiporter: moves two substances in opposite directions

Primary active transport

requires direct hydrolysis of ATP to drive movement of specific ions against their concentration gradients

Secondary active transport

energy comes from an ion concentration gradient that is established by primary active transport

Eukaryotic cells may take up and release fluids, large molecules, and smaller cells via

endocytosis

What is phagocytosis?

molecules or entire cells are engulfed

What is pinocytosis?

a vesicle forms to bring small dissolved substances or fluids into a cell

Receptor-mediated endocytosis

molecules at the cell level service recognize and trigger uptake of specific molecules

Top Hat: Which statement about diffusion is true?

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a

The concentration gradient of a solute depends on the size of the molecule.

b

Equilibrium in a solution is the end point of diffusion.

c

The net movement of particles depends on the temperature of the solution.

d

Diffusion is most efficient over long distances.

e

Diffusion can reduce selective permeability of a membrane.

B

rate of diffusion

Review

You are monitoring the diffusion of a molecule across a membrane. Of the options listed below, the fastest rate of diffusion would result from an internal concentration of ____ µM and an external concentration of ____ µM.

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a

5; 60

b

35; 40

c

50; 40

d

50; 50

e

100; 120

A

osmosis

Review

Solution X is hypotonic relative to solution Y if…

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a

X has a solute concentration that is lower than the solute concentration of Y.

b

Y has a greater volume of fluid than X.

c

X and Y have equal amounts of solute but Y has a greater volume of fluid.

d

X has a solute concentration that is higher than the solute concentration of Y.

e

X and Y have equal volumes of fluid but X has a greater amount of solute.

A

If a cell has an increased need for a particular molecule already present in a higher concentration within the cell than in the extracellular fluid, the cell might use active transport, which usually moves molecules

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a

in the same direction as diffusion moves them.

b

in a direction opposite to the one in which diffusion moves them.

c

in a direction that tends to bring about equilibrium.

d

toward higher pH.

e

from inside to outside the cell.

B

What is signal transduction?

• Definition: Signal transduction is the process by which cells convert external signals into specific cellular responses.

• Importance: It plays a crucial role in various biological processes, including cell growth, development, and immune response.

• Steps: Signal reception, signal transduction, and cellular response.

• Signaling molecules: Hormones, neurotransmitters, growth factors, and cytokines.

• Key components: Receptors, second messengers, protein kinases, and transcription factors.

• Examples: cAMP, MAPK, and PI3K/Akt signaling pathways.

• Regulation: Feedback loops, cross-talk, and desensitization mechanisms.

• Diseases: Dysregulation of signal transduction can lead to cancer, diabetes, and neurological disorders.

All cells process information from the environment when a _____ binds to a ______

ligand, receptor

Justacrine signals

bind to adjacent cells in contact with the secreting cells

Autocrine signals

bind to the receptors on the cell that secretes them

Paracrine signals

bind to receptors on nearby cells m

What are hormones

signals that travel to distant cells, often using the circulatory system

Ion channel linked receptors

allows ions to enter or leave a cell

• signal binding results in a change in share of the channel protein. This results in the channel opening.

• Ex: the acetylcholine receptor

  • The signal is acetylcholine

  • When the channel is open, sodium ions enter the cell

Protein kinase receptors

catalyze phosphorylation of themselves and/or other proteins to change their shapes and functions

Ligand binding to a G protein-coupled receptor activates a

a protein called a G protein

Both primary and secondary active transport

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a

generate ATP.

b

are based on passive movement of Na+ ions.

c

include the passive movement of glucose molecules.

d

use ATP directly.

e

can move solutes against their concentration gradients.

E

Endocytosis

Review

An important difference between phagocytosis and receptor-mediated endocytosis is that

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a

in phagocytosis, the membrane forms coated vesicles.

b

vesicles do not form in receptor-mediated endocytosis.

c

dissolved substances can be taken up by phagocytosis.

d

receptor-mediated endocytosis is more specific.

e

macromolecules can enter through receptor-mediated endocytosis.

D

Classification of ACh

Review

Acetylcholine (ACh) is a molecule released by a neuron. That ACh diffuses across the extracellular space to a nearby neuron, where it binds and initiates a response. How would you classify acetylcholine?

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a

Juxtacrine signal

b

Paracrine signal

c

Hormone

d

Temporal signal

e

Autocrine signal

B

General signal transduction

Review

Which is the correct order of the steps in a generalized signal transduction pathway?

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a

Signal molecule activates target cell → target cell binds to receptor → receptor is activated

b

Signal molecule is secreted by nearby cell → signal molecule enters cell → signal activates receptor

c

Signal molecule enters nucleus → signal molecule binds to DNA → transcription of specific genes occurs

d

Signal molecule binds to receptor → molecules within cell transduce signal → cell responds

D

in the brain _____ binds to its _____ to inhibit wakefulness

adenosine, receptor

When an _____ binds to a receptor, it has the same effect as the natural ligand

agonist

When an ______ binds to a receptor, it prevents the ligand from binding and does not trigger a response

antagonist

Intracellular receptors

respond to signals that can cross the cell membrane

• many are transcription factors

• Transcription factors change the expression of genes in a cell

What are the three kinds of eukaryotic membrane receptors

Ion channel linked receptors - ligand binding allows ions to enter or leave a cell

protein kinase receptors - ligand binding activates a protein kinase cascade, which can lead to short-or-long term responses in the cell

G protein coupled receptors - ligand binding activates the production of a secondary messenger, which can lead to short-or-long term responses in the cell

A protein kinase cascade can amplify an intracellular signal by…

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a

opening gap junctions to allow diffusion of signals from neighboring cells.

b

using nitric oxide to quickly diffuse into cells, amplifying the response.

c

using transcription factors to increase gene expression.

d

activating one kinase molecule that can then trigger the activation of many proteins.

D

After a ligand binds to a G protein coupled receptor and activates a G protein, what happens next?

The active G protein activates an effector protein

G proteins are active when bound to ____

GTP

What is cAMP

a second messenger that amplifies and distributes a signal. cAMP is produced from ATP be effector protein adenylyl cyclase.

Second messengers are…

signaling molecules that increase in concentration inside a cell in response to a signaling molecule that binds at the surface

• amplify the signal in a signal transduction pathway

What is happening in the photo

cAMP relays and amplifies the signal coming from Epinephrine by activating Protein Kinase A

Protein Kinase A is activated by…

high concentration of cAMP

Examples of second messengers

cAMP - produced by Adenylyl cyclase following GCPR activation, increase in cAMP concentration can activate PKA

IP3 and DAG - produced by Phospholipase C following GCPR activation

Ca2+ - release into the cytosol following GPCR activation, can help activate PKC

Nitric Oxide - produced following activation of the acetylcholine receptor

IP3 and DAG are…

second messengers made from the phospholipids in the cell membrane

Hydrolysis of PIP2 by…

Phospholipase C makes IP3 and DAG

IP3 binds to and activates a _____

Ca2+ channel in the ER membrane, which release stores of Ca2+ from the ER into the cytosol

Increased Ca2+ helps activate…

Protein Kinase C (PKC)

Ca2+ bound PKC binds to DAG, which

fully activates it

What is nitric oxide

a second messenger that acts between acetylcholine and the relaxation of smooth muscle in blood vessels

What are the three ways that cells respond to signals

opening ion channels, changing enzyme activity, differential gene expression

How are signal transduction pathways turned off?

GTPases can hydrolyze GTP into GDP, which inactivates the G protein or second messengers can be degraded

When is a signal tranduction pathway not regulated properly

when a signal transduction pathway is not activated or inactivated correctly

A ligand binds to the membrane receptor...

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a

inside the cell.

b

outside the cell.

c

Both A and B can be true.

d

Neither A nor B are ever true.

B

Antagonists differ from agonists because they...

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a

trigger a response from the receptor.

b

trigger a response more slowly than agonists.

c

trigger a response more quickly than agonists.

d

do not trigger a response from the receptor.

D

Which of these is directly activated by a hormone binding to a GPCR?

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a

The effector protein

b

Adenylyl cyclase

c

The G protein

d

A protein kinase

e

cAMP

C

When the G protein is active, ___ has been replaced by ____.

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a

GTP; GDP

b

GDP; GTP

c

cAMP; GTP

d

GTP;cAMP

B

Adenylyl cyclase is then activated by...

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a

being phosphorylated by a kinase.

b

the creation of cAMP from ATP.

c

the creation of GTP from GDP.

d

the active G protein.

D

When adenylyl cyclase is activated and undergoes a conformational change, it will...

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a

make ATP from cAMP.

b

make cAMP from ATP.

c

make ADP from ATP.

d

make ATP from ADP.

B