Biochemistry 2280A Study Guide - Midterm Guide: Lipid Bilayer, Electrochemical Gradient, Passive Transport

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30 Apr 2018

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Biochemistry 2280 – Midterm

Membrane Proteins

Describe the different functions membrane proteins can perform

Transporter and channels

• ions and polar molecules need to be moved between the compartments of the cell, or

between the inside and the outside (facilitated transport)

- transporters undergo conformational changes to move them across the

membrane

- channels (when open) form continuous pores through the bilayer

- most transporters and channels are specific for particular substrate or small

set of them

• if the concentration of an ion or molecule is larger on one side, there will be net

movement of the ion toward the side of lower concentration (if a pathway across the

membrane exists)

- same if there is a charged difference

across the membrane — electrochemical

gradient

• active transport; a source of energy is used

• passive transport; a pathway is provided via a

transporter or channel but no energy — they will

spontaneously move

Anchors

• structural proteins that provide stability to the membrane

• helps control the shape of the cell and its positive relative to other cells

• they bind to other macromolecules on one or both sides of the membrane

Receptors

• sense chemical signals on the outside of the cell and carry the message to the inside

of the cell

• most recognize a very specific molecular signal

Enzymes

• catalyze chemical reactions; many receptors will have enzymatic activity

Explain in basic terms how polar or charged molecules can move across membranes

- often they an’t get across at first because of charge

- then one charge is all stuck on one side (ex. positive)

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Document Summary

Describe the different functions membrane proteins can perform. Transporter and channels: ions and polar molecules need to be moved between the compartments of the cell, or between the inside and the outside (facilitated transport) Transporters undergo conformational changes to move them across the membrane. Channels (when open) form continuous pores through the bilayer. Anchors: structural proteins that provide stability to the membrane, helps control the shape of the cell and its positive relative to other cells, they bind to other macromolecules on one or both sides of the membrane. Receptors: sense chemical signals on the outside of the cell and carry the message to the inside of the cell, most recognize a very specific molecular signal. Enzymes: catalyze chemical reactions; many receptors will have enzymatic activity. Explain in basic terms how polar or charged molecules can move across membranes. Often they (cid:272)an"t get across at first because of charge. Then one charge is all stuck on one side (ex. positive)

Related Questions

Cellular biology answer check. please check if my answers arecorrect or not.

1) The concentration of ions inside a cell is the same as theirconcentration outside of the cell. True or false? (i chose falsesince having equilibrium inside a cell is bad)

2) Membrane transport proteins...

a)...transport membrane potentials between cells

b)	...transport membranes from the ER to the Golgi

c)	...are made up of phospholipids

d)	...transport molecules across membranes

i chose d

3)The electrochemical gradienttakes into account:

a)	The concentration of solutes on either side of themembrane.

b)	The overall charge on either side of the membrane.

c)	Both of these.

i chose C. (although i am sure that overall charge matters, Iwasn't sure if concentration of solutes are taken account.)

4) If no energywere expended by an animal cell:

a)	Both gradients would be depleted

b)The K+ gradient would maintain itself.

c)	None of these

d)	The Na+ gradient would maintain itself.

I chose d) mainly because I think Na+ gradient exist in animalcell and not K+ gradient.

5) Which of the following is a true statement aboutactin?

a)	Once actin has polymerized, it never depolymerizes.

b)	Actin is a transmembrane protein.

c)	Actin can form branched networks.

d)	Actin filaments are organized into hollow tubes.

I chose c. can't explain why.

6)Ion channels:

a)	Form a hydrophobic channel through the membrane

b)	Have filters that let sugars through

c)	Are selective for particular ions (only the

taupeshark376

1. The plasma membrane of liver cells contains a glucose uniportthat transports glucose by facilitated diffusion. When the[glucose] is higher inside the liver cell than the [glucose]outside the liver cell, the glucose uniport will

A. couple the transport of glucose out of the cell to thehydrolysis of ATP

B. couple the transport of glucose into the cell to thehydrolysis of ATP

C. switch to a closed conformation, allowing no transport ofglucose

D. transport glucose out of the cell by passive transport

E. transport glucose in of the cell by passive transport

2. Unlike the positive charged ion shown in the middle diagramof figure 11-4B, K+ is higher in concentration inside the cell. Howwill the membrane potential of a cell at rest (shown in both themiddle and right-hand diagrams of Figure 11-4B) affect theelectrochemical gradient for K+?

A. The membrane potential will increase the electrochemicalgradient

B. The membrane potential will decrease the electrochemicalgradient

C. The membrane potential will have no effect on theelectrochemical gradient

3. Which of the following proteins carries out activetransport?

A. gluclose symport

B. Bacteriorhodopsin

C. ABC transporter

D. NA K pump

E. All of the above

4. Aquaporin will not transport Na+ ions because

A. Two asparagine residues in the channel prevent the passage ofNa+ ions by binding the oxygen of each water molecule as it passesby

B. Na+ ions are repelled by the positive charges at the entranceto the channel

C. Na+ ions cannot make contact with the carbonyl (C=O) groupson all four sides of the channel

D. The passage of Na+ ions is energetically unfavorable becauseone side of the channel is hydrophobic in nature

5. The acetylcholine receptor is different from other channelproteins we have discussed, such as the K+ leak channel,because

A. The acetylcholine channel is composed of a single polypeptiderather than multiple subunits

B. The acetylcholine channel transports Na+ ions against theconcentration gradient for sodium

C. The acetylcholine channel has a much smaller diameter thanother channel proteins

D. The acetylcholine channel transports ions with theirassociated shell of water molecules

E. The acetylcholine channel is always open, and never switchesto a closed conformation

6. After opening briefly along the axon of a neuron,voltage-gated ion channels switch to an inactivated conformationthat slowly returns to the original closed conformation of theprotein. This slow change in conformation, requiring about amillisecond, is important because

A. all of the ions that were transported across the membranewhen the ion channels were open must be actively transported backto the other side of the membrane, restoring the originalconcentration gradient, before the ion channels can open again

B. ATP hydrolysis is necessary to drive this energeticallyunfavorable change in conformation

C. it prevents the action potential from reversing direction andtraveling back toward the cell body of the neuron

D. the channel protein must be dephosphorylated in order tocomplete the transport process and return to the originalnonphosphorylated conformation

limeelephant476

Cells from which domain(s) of life are separated from theirenvironment by a plasma membrane? Select all correct choices.bacteria archaea eukarya 2. The active maintenance of a constantenvironment is referred to as: stability. homeostasis. symmetry.equilibrium. balance. 3. The electrical component of anelectrochemical gradient is due to: the use of ATP as an energysource to drive primary transport. a greater concentration ofpositive charges on the side of the membrane with the highestconcentration of protons. a greater concentration of positivecharges on the side of the membrane with the lowest concentrationof protons. a higher pH on the side of the membrane with the lowestconcentration of protons. a higher pH on the side of the membranewith the highest concentration of protons. 4. Which one of thefollowing would be found in the cells of a blade of grass but notin the cells of an insect feeding on that grass? Select all correctchoices. chloroplasts cytoskeletal elements mitochondriaendoplasmic reticulum nuclei 5. With which of the following is asignal-recognition particle (SRP) capable of interacting? Selectall correct choices. a signal sequence in a protein destined forthe ER a ribosome an SRP receptor 6. Which one of the followingcellular compartments does not have a double membrane structureseparating it from the rest of the cell? Select all correctchoices. mitochondria chloroplasts lysosomes the nucleus 7. True orFalse: purified phospholipids will gather together and formmembranes only if the appropriate enzyme is present. false true 8.Which component(s) of a phospholipid would most likely be found inthe interior of a lipid bilayer? Select all correct choices.glycerol fatty acids phosphate 9. Some drugs are now beingdelivered into cells through liposomes, where the drug issurrounded by a phospholipid bilayer. How do the drugs enter intothe cell? The liposome fuses with the phospholipid bilayer of thecell. The drug destroys the liposome and is transported viadiffusion into the cell. Protein channels on the cell surfacetransport the liposomes into the cell. The liposome cuts a hole inthe cell and injects the drug into the cell. 10. Some diseases canresult from defective transport across the membrane. For example,cystic fibrosis results from a chloride ion transporter that doesnot function. Which of the following would be affected when thistransporter does not function? the electrical gradient of the cellthe chloride concentration gradient Neither the chlorideconcentration gradient nor the electrical gradient of the cell Boththe chloride concentration gradient and the electrical gradient ofthe cell

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Biochemistry 2280A Study Guide - Midterm Guide: Lipid Bilayer, Electrochemical Gradient, Passive Transport

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