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freshman > biology EXAM #3 pt.1 > Flashcards

biology EXAM #3 pt.1 Flashcards

1
Q

the plasma membrane

what is it

exhibits

it allows

transports

A

the boundary that separates the living cell from its surroundings

Exhibits selective permeability

It allows some substances to cross it more easily than others

Transport proteins are often responsible for controlling passage across cellular membranes

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2
Q

The fluid mosaic model of membrane structure

A

States that a membrane is a fluid structure of lipids with a “mosaic” of various proteins embedded in it

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3
Q

Phospholipids
Are the most abundant

Are… , containing

The _______________ of the phospholipids are….

A

Are the most abundant lipid in the plasma membrane

Are amphipathic, containing both hydrophobic and hydrophilic regions

The hydrophobic tails of the phospholipids are sheltered inside the membrane, while the hydrophilic heads are exposed to water on either side

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4
Q

In the fluid mosaic model,

Proteins are not

A

the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

randomly distributed in the membrane

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5
Q

Phospholipids in the plasma membrane held together by ____________________.

Lipids and proteins can

Rarely, a lipid may

A

weak hydrophobic interactions

move sideways within the bilayer.

flip-flop across the membrane, from one phospholipid layer to the other

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6
Q

Membranes must be….; fluidity affects:

Membranes that are too

Organisms living in extreme temperatures have

A

fluid to work properly; fluidity affects both permeability and movement of transport proteins

fluid cannot support protein function

adaptive differences in membrane lipid composition

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7
Q

The type of hydrocarbon tails in phospholipids affects

______________ also affect the fluidity

A

the fluidity of the plasma membrane, the more unsaturated, the more fluidity of the membrane.

Temperature

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8
Q

The steroid cholesterol has different effects (temperature buffer) on membrane fluidity at different temperatures:

–At moderate ºT :
–At low ºT :

Plants use different but related…

A

-it reduces fluidity by reducing mobility of phospholipids, 

-it prevents solidifications by disrupting regular packaging of phospholipids

steroid lipids to buffer membrane fluidity

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9
Q

Variations in lipid composition of cell membranes of many species appear to be

Ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary
example, cell membranes have a high proportion of unsaturated hydrocarbon tails in fish that live in extreme cold
example, in winter wheat, the percentage of unsaturated phospholipids increases in autumn to prevent membrane solidification during winter

A

adaptations to specific environmental conditions

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10
Q

A membrane

Proteins determine most of the

A

is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

membrane’s functions

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11
Q

INTEGRAL PROTEINS
Penetrate the
Are often

A

hydrophobic core of the lipid bilayer

transmembrane proteins, completely spanning the membrane

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12
Q

Peripheral proteins:
Are

Some proteins:
are attached to __________, others attached to________

The hydrophobic regions of an integral protein consist of

A

are appendages loosely bound to the surface of the membrane

-cytoskeleton; fibers of the ECM

one or more stretches of nonpolar amino acids, often coiled into α helices

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13
Q

Cell-surface membranes can carry out several functions:

A

Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)

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14
Q

TRANSPORT

A

A protein that spans the membrane
may provide a hydrophilic channel across the
membrane that is selective for a particular solute.

Other transport proteins shuttle a substance
from one side to the other by changing shape. Some
of these proteins hydrolyze ATP as an energy source
to actively pump substances across the membrane.

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15
Q

ENZYMATIC ACTIVITY

A

A protein built into the membrane
may be an enzyme with its active site exposed to
substances in the adjacent solution. In some cases,
several enzymes in a membrane are organized as
a team that carries out sequential steps of a
metabolic pathway.

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16
Q

SIGNAL TRANSDUCTION

A

A membrane protein may have
a binding site with a specific shape that fits the shape
of a chemical messenger, such as a hormone. The
external messenger (signal) may cause a
conformational change in the protein (receptor) that
relays the message to the inside of the cell.

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17
Q

CEL-CELL RECOGNITION

A

Some glyco-proteins serve as
identification tags that are specifically recognized
by other cells.

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18
Q

INTERCELLULAR JOINING

A

Membrane proteins of adjacent cells
may hook together in various kinds of junctions, such as
gap junctions or tight junctions

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19
Q

ATTACHMENT TO THE CYTOSKELETON AND THE EXTRACELLULAR MATRIX

A

Microfilaments or other elements of the
cytoskeleton may be bonded to membrane proteins,
a function that helps maintain cell shape and stabilizes
the location of certain membrane proteins. Proteins that adhere to the ECM can coordinate extracellular and
intracellular changes

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20
Q

____________ proteins are important in the medical field
For example, HIV must bind to the immune cell-surface protein CD4 and a “co-receptor” CCR5 in order to infect a cell
HIV cannot enter the cells of resistant individuals who lack CCR5
Drugs are now being developed to mask the CCR5 protein

A

Cell-surface

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21
Q

Cells recognize each other by

Membrane carbohydrates may be covalently bonded to

Carbohydrates on the extracellular side of the plasma membrane vary

A

binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane

lipids (forming glycolipids) or, more commonly, to proteins (forming glycoproteins)

among species, individuals, and even cell types in an individual

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22
Q

Proteins in the plasma membrane can ____________________, others are ____________

A

drift within the bilayer, inmobile due to their attachment to the cytoskeleton

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23
Q

Cell-cell recognition:
Is a cell’s ability to :

Membrane carbohydrates:
Interact with the ….
Use ______ and ________

A

distinguish one type of neighboring cell from another

surface molecules of other cells, facilitating cell-cell recognition

glycoproteins, glycolipids

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24
Q

Membranes have distinct

This affects the movement of proteins synthesized in

The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is

A

inside and outside faces

the endomembrane system

determined when the membrane is built by the ER and Golgi apparatus

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25
Q

Membrane proteins and lipids

A

Are synthesized in the ER and Golgi apparatus

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26
Q

A cell must exchange materials with its surroundings, a process controlled by the

A

plasma membrane

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27
Q

Hydrophobic molecules examples:

Are…

Hydrophilic molecules including ions and polar (like glucose) molecules do not…

Proteins built into the membrane play key roles in

A

(hydrocarbons, oxygen, carbon dioxide)

lipid soluble and can pass through the membrane rapidly

cross the membrane easily

regulating transport

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28
Q

Transport proteins allow

Some transport proteins, called ____________, have a:

Channel proteins called _________ greatly facilitate the:

They are composed of

Overall, up to

A

passage of hydrophilic substances across the membrane

channel proteins: hydrophilic channel that certain molecules or ions can use as a tunnel

aquaporins: passage of water molecules
four polypeptide subunits that each form a channel for the passage of water

3 billion water molecules pass through per second

29
Q

Other transport proteins, called ____________, bind to

A transport protein is specific for the

A

carrier proteins: molecules and change shape to shuttle them across the membrane

substance 
it moves

30
Q

Molecules transport by means of

A

passive (diffusion, osmosis, facilitated by channel proteins) and active transport (carrier proteins, exocytosis and endocytosis).

31
Q

Passive transport is

A

diffusion of a substance across a membrane with no energy investment


32
Q

Diffusion

Is

Each substances diffuse down its own concentration gradient, unaffected by the concentration of other substances.

It diffuses because of the

A

the movement of molecules from a region of higher concentration to a region of lower concentration.

difference in concentration of the substance from one area to another, from high to low concentration until it reaches equilibrium.

33
Q

Diffusion of one solute.

A

The membrane has pores large enough for molecules
of dye to pass through. Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more molecules. The dye diffuses from where it is more concentrated to where it is less concentrated. This leads to a dynamic equilibrium: The solute molecules continue to cross the membrane, but at equal rates in both directions.

34
Q

Diffusion of two solutes.

A

Solutions of two different dyes are separated by a membrane that is permeable to both. Each dye diffuses down its own concentration gradient. There will be a net diffusion of the purple dye toward the left, even though the total solute concentration was initially greater on the left side.

35
Q

Substances diffuse down their own concentration gradient, the region along which

No work must be done to move substances down the concentration gradient.

The diffusion of a substance across a biological membrane is

A

the density of a chemical substance increases or decreases.

passive transport because no energy is expended by the cell to make it happen.

36
Q

Osmosis

Is

Free water molecules diffuse across

Water keeps moving until the solute concentration is equal on both sides

A

the movement of water (water molecules not clustered around another substance) across a selectively permeable membrane

a membrane from the region of lower solute concentration to the region of higher solute concentration

37
Q

Tonicity
Is the ability of a

The tonicity of a solution depends on

Has a great impact on

A

solution to cause a cell to gain or lose water

its concentration of solutes that cannot cross the membrane relative to that inside the cell

cells without walls

38
Q

If a solution is isotonic
The concentration of solutes is

There will be no

The volume of a cell without a cell wall is

A

the same as it is inside the cell

net movement of water

stable in an isotonic solution

39
Q

If a solution is hypertonic
The concentration of solutes is

The cell will

Net diffusion of water is from

Cells without cell walls will

Cells without cell walls will ________ in hypertonic solution

A

greater than it is inside the cell

lose water

inside the cell to the surrounding solution

lose water, shrivel, and likely die in hypertonic solution

shrivel

40
Q

If a solution is hypotonic

The concentration of solutes is

Net diffusion of water is from

The cell will

Cells without cell walls will _______ in a hypotonic solution

A

less than it is inside the cell

the surrounding solution to the inside of the cell

gain water

lyse (burst)

41
Q

Cell walls:

Help maintain
If a plant cell is turgid: -It is in a _______ environment
-It is very firm, a healthy state in most plants

If a plant cell is flaccid
-It is in an ________________ environment

A

water balance
-hypotonic

-isotonic or hypertonic

42
Q

Hypotonic or hypertonic environments cause problems for cells without walls because

Organisms that live in such environments require a method of

For example, Paramecium live in a hypotonic environment; they have a contractile vacuole to pump excess water out of the cell

A

they cannot tolerate excessive water loss or uptake

osmoregulation, control of solute concentration and water balance

43
Q

Bacteria and archaea living in hypersaline (excessively salty) environments have mechanisms to ensure that water does not leave the cell

A
44
Q

A plant cell in a hypotonic solution

If a plant cell and its surroundings are isotonic, there is

A

swells until the wall opposes uptake; the cell is now turgid (firm)

no net movement of water into the cell; the cell becomes flaccid (limp)

45
Q

In a hypertonic environment,

What happens?
lethal effect called

A

plant cells lose water

The membrane pulls away from the cell wall, causing the plant to wilt, a potentially lethal effect called plasmolysis

46
Q

Transport proteins:
Allow passage of

In facilitated diffusion (Passive Transport Aided by Proteins)

Transport proteins…

A

hydrophilic substances across the membrane

speed the movement of molecules across the plasma membrane

47
Q

Channel proteins provide

Aquaporins facilitate

Ion channels facilitate

Some ion channels, called __________,

For example, in nerve cells, ion channels open in response to electrical stimulus

Other gated channels open in response to chemical stimulus—binding of a specific substance to the protein

A

corridors that allow a specific molecule or ion to cross the membrane

the diffusion of water

the transport of ions

gated channels, open or close in response to a stimulus

48
Q

Carrier proteins undergo a

This can be triggered by

Carrier proteins involved in facilitated diffusion move

A

subtle shape change that moves the solute-binding site across the membrane

the binding and release of the transported molecule

substances down their concentration gradients; no energy input is required

49
Q

Channel proteins

A

Provide corridors that allow a specific molecule or ion to cross the membrane

50
Q

Active transport:
Moves substances

Requires

All proteins involved in active transport are

A

against their concentration gradient

energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients

carrier proteins

51
Q

nada

A

mada

52
Q

Active transport allows cells to

For example, an animal cell has a much higher potassium (K+) and a much lower sodium (Na+) concentration compared to its surroundings
This is controlled by the sodium-potassium pump, a transport protein that is energized by transfer of a phosphate group from the hydrolysis of ATP

A

maintain concentration gradients that differ from their surroundings

53
Q

The sodium-potassium pump


A

buscar video or sumn

54
Q

Membrane potential is

Voltage is created by

The inside of the cell is

A

the voltage across a membrane

differences in the distribution of positive and negative ions across a membrane

negative in charge relative to the outside, favoring passive transport of cations into and anions out of the cell

55
Q

Two combined forces, collectively called the _________ _________, drive the :

the forces
-__________
-____________

An ion diffuses…

A

electrochemical gradient, drive the diffusion of ions across a membrane

A chemical force
An electrical force

down its electrochemical gradient

56
Q

An electrogenic pump is a

The main electrogenic pump differs between

In animals,

The main electrogenic pump of plants, fungi, and bacteria is a _______ _______, which actively transports

A

transport protein that generates voltage across a membrane, storing energy that can be used for cellular work

plants and animals

it is the sodium-potassium pump

proton pump, transports hydrogen ions (H+) out of the cell

57
Q

“electrogenic pump topic”

_______________ is the major electrogenic pump of animal cells

Example 
the H+ gradient generated in ETS in aerobic cellular respiration and the light reaction of photosynthesis, 
also the Na+ K+ pump.

Electrogenic pumps help

A

The sodium-potassium pump

store energy that can be used for cellular work

58
Q

Cotransport
Occurs when

The diffusion of an actively transported solute down its concentration gradient is coupled with the

Cotransport:

A

active transport of a specific solute indirectly drives the active transport of another solute

transport of a second substance against its own concentration gradient

active transport driven by a concentration gradient

59
Q

Plant cells use proton pumps to generate

A cotransporter couples the movement of

This is how plants

A

an H+ gradient across the cell membrane

H+ back down its concentration gradient to the active transport of sucrose into the cell

load sucrose into their veins for transport around the plant body

60
Q

Animal cells use a

Sodium potassium pumps actively transport

Normally, sodium in waste is reabsorbed in __ ______ to:

A

similar cotransporter to couple the active transport of glucose to the diffusion of Na+ into cells lining the intestine

Na+ out of the cell to maintain the electrochemical gradient

the colon to maintain a constant level in the body

61
Q

When a person has diarrhea,

A rapid drop in ________ can be life-threatening

Drinking a concentrated ______ and _______ solution enables :

A

waste is expelled too fast for reabsorption, causing sodium levels to drop

sodium

salt (N a C l) and glucose, enables uptake through the N a+/glucose transporters in the intestine

62
Q

Bulk transport across the plasma membrane occurs by

Large proteins like ___________ and __________,
Cross:
They require :

A

exocytosis and endocytosis

polysaccharides and proteins, Cross the membrane in bulk via vesicles and by different mechanisms

energy

63
Q

In endocytosis, the cell takes in

Endocytosis is a reversal of

There are three types of endocytosis:

A

macromolecules by forming vesicles from the plasma membrane

exocytosis, involving different proteins

Phagocytosis (“cellular eating”)
Pinocytosis (“cellular drinking”)
Receptor-mediated endocytosis

64
Q

In Phagocytosis, a cell

The vacuole fuses with a _________ to :

A

engulfs a particle by extending pseudopodia around it and packing it in a membranous sac called a food vacuole

lysosome to digest the particle

65
Q

In Pinocytosis, molecules are

Pinocytosis is nonspecific for ….

any and all solutes are

Parts of the plasma membrane that form vesicles are

A

taken up when extracellular fluid is “gulped” into tiny vesicles

the substances it transports

taken into the cell

lined on the inner side with coat proteins, forming coated vesicles

66
Q

In receptor-mediated endocytosis, vesicle formation is

Receptor proteins bound to specific solutes from the extracellular fluid are

Emptied receptors are

A

triggered by solute binding to receptors

clustered in coated pits that form coated vesicles

recycled to the plasma membrane by the same vesicle

67
Q

Human cells use receptor-mediated endocytosis to:
, which is carried in particles called:

Individuals with familial hypercholesterolemia have missing or defective L D L receptor proteins

Cholesterol accumulates in the blood, building up lipids and narrowing the space in the blood vessels, resulting in potential heart damage or stroke

A

take in cholesterol
low-density lipoproteins (LDLs)

68
Q

In exocytosis transport,

Many secretory cells use exocytosis to

For example, cells in the pancreas secrete insulin by exocytosis

A

vesicles migrate to the plasma membrane, fuse with it, and release their contents outside the cell

export 
their products

69
Q

The Davson-Danielli sandwich model of membrane structure
Stated that the membrane was

model was supported by

A

made up of a phospholipid bilayer sandwiched between two protein layers

electron microscope pictures of membranes

freshman (25 decks)

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