biology EXAM #3 pt.1

Question 1

the plasma membrane

what is it

exhibits

it allows

transports

Answer 1

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

Question 2

The fluid mosaic model of membrane structure

Answer 2

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

Question 3

Phospholipids
Are the most abundant

Are… , containing

The _______________ of the phospholipids are….

Answer 3

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

Question 4

In the fluid mosaic model,

Proteins are not

Answer 4

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

randomly distributed in the membrane

Question 5

Phospholipids in the plasma membrane held together by ____________________.

Lipids and proteins can

Rarely, a lipid may

Answer 5

weak hydrophobic interactions

move sideways within the bilayer.

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

Question 6

Membranes must be….; fluidity affects:

Membranes that are too

Organisms living in extreme temperatures have

Answer 6

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

fluid cannot support protein function

adaptive differences in membrane lipid composition

Question 7

The type of hydrocarbon tails in phospholipids affects

______________ also affect the fluidity

Answer 7

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

Temperature

Question 8

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…

Answer 8

-it reduces fluidity by reducing mobility of phospholipids, 

-it prevents solidifications by disrupting regular packaging of phospholipids

steroid lipids to buffer membrane fluidity

Question 9

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

Answer 9

adaptations to specific environmental conditions

Question 10

A membrane

Proteins determine most of the

Answer 10

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

membrane’s functions

Question 11

INTEGRAL PROTEINS
Penetrate the
Are often

Answer 11

hydrophobic core of the lipid bilayer

transmembrane proteins, completely spanning the membrane

Question 12

Peripheral proteins:
Are

Some proteins:
are attached to __________, others attached to________

The hydrophobic regions of an integral protein consist of

Answer 12

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

Question 13

Cell-surface membranes can carry out several functions:

Answer 13

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

Question 14

TRANSPORT

Answer 14

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.

Question 15

ENZYMATIC ACTIVITY

Answer 15

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.

Question 16

SIGNAL TRANSDUCTION

Answer 16

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.

Question 17

CEL-CELL RECOGNITION

Answer 17

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

Question 18

INTERCELLULAR JOINING

Answer 18

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

Question 19

ATTACHMENT TO THE CYTOSKELETON AND THE EXTRACELLULAR MATRIX

Answer 19

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

Question 20

____________ 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

Answer 20

Cell-surface

Question 21

Cells recognize each other by

Membrane carbohydrates may be covalently bonded to

Carbohydrates on the extracellular side of the plasma membrane vary

Answer 21

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

Question 22

Proteins in the plasma membrane can ____________________, others are ____________

Answer 22

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

Question 23

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

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

Answer 23

distinguish one type of neighboring cell from another

surface molecules of other cells, facilitating cell-cell recognition

glycoproteins, glycolipids

Question 24

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

Answer 24

inside and outside faces

the endomembrane system

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

Question 25

Membrane proteins and lipids

Answer 25

Are synthesized in the ER and Golgi apparatus

Question 26

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

Answer 26

plasma membrane

Question 27

Hydrophobic molecules examples: Are... Hydrophilic molecules including ions and polar (like glucose) molecules do not... Proteins built into the membrane play key roles in

Answer 27

(hydrocarbons, oxygen, carbon dioxide) lipid soluble and can pass through the membrane rapidly cross the membrane easily regulating transport

Question 28

Transport proteins allow Some transport proteins, called ____________, have a: Channel proteins called _________ greatly facilitate the: They are composed of Overall, up to

Answer 28

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

Question 29

Other transport proteins, called ____________, bind to A transport protein is specific for the

Answer 29

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

Question 30

Molecules transport by means of

Answer 30

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

Question 31

Passive transport is

Answer 31

diffusion of a substance across a membrane with no energy investment


Question 32

Diffusion Is Each substances diffuse down its own concentration gradient, unaffected by the concentration of other substances. It diffuses because of the

Answer 32

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.

Question 33

Diffusion of one solute.

Answer 33

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.

Question 34

Diffusion of two solutes.

Answer 34

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.

Question 35

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

Answer 35

the density of a chemical substance increases or decreases. passive transport because no energy is expended by the cell to make it happen.

Question 36

Osmosis Is Free water molecules diffuse across Water keeps moving until the solute concentration is equal on both sides

Answer 36

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

Question 37

Tonicity Is the ability of a The tonicity of a solution depends on Has a great impact on

Answer 37

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

Question 38

If a solution is isotonic The concentration of solutes is There will be no The volume of a cell without a cell wall is

Answer 38

the same as it is inside the cell net movement of water stable in an isotonic solution

Question 39

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

Answer 39

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

Question 40

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

Answer 40

less than it is inside the cell the surrounding solution to the inside of the cell gain water lyse (burst)

Question 41

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

Answer 41

water balance -hypotonic -isotonic or hypertonic

Question 42

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

Answer 42

they cannot tolerate excessive water loss or uptake osmoregulation, control of solute concentration and water balance

Question 43

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

Question 44

A plant cell in a hypotonic solution If a plant cell and its surroundings are isotonic, there is

Answer 44

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)

Question 45

In a hypertonic environment, What happens? lethal effect called

Answer 45

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

Question 46

Transport proteins: Allow passage of In facilitated diffusion (Passive Transport Aided by Proteins) Transport proteins...

Answer 46

hydrophilic substances across the membrane speed the movement of molecules across the plasma membrane

Question 47

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

Answer 47

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

Question 48

Carrier proteins undergo a This can be triggered by Carrier proteins involved in facilitated diffusion move

Answer 48

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

Question 49

Channel proteins

Answer 49

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

Question 50

Active transport: Moves substances Requires All proteins involved in active transport are

Answer 50

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

Question 51

nada

Answer 51

mada

Question 52

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

Answer 52

maintain concentration gradients that differ from their surroundings

Question 53

The sodium-potassium pump


Answer 53

buscar video or sumn

Question 54

Membrane potential is Voltage is created by The inside of the cell is

Answer 54

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

Question 55

Two combined forces, collectively called the _________ _________, drive the : the forces -__________ -____________ An ion diffuses...

Answer 55

electrochemical gradient, drive the diffusion of ions across a membrane A chemical force An electrical force down its electrochemical gradient

Question 56

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

Answer 56

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

Question 57

"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

Answer 57

The sodium-potassium pump store energy that can be used for cellular work

Question 58

Cotransport Occurs when The diffusion of an actively transported solute down its concentration gradient is coupled with the Cotransport:

Answer 58

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

Question 59

Plant cells use proton pumps to generate A cotransporter couples the movement of This is how plants

Answer 59

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

Question 60

Animal cells use a Sodium potassium pumps actively transport Normally, sodium in waste is reabsorbed in __ ______ to:

Answer 60

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

Question 61

When a person has diarrhea, A rapid drop in ________ can be life-threatening Drinking a concentrated ______ and _______ solution enables :

Answer 61

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

Question 62

Bulk transport across the plasma membrane occurs by Large proteins like ___________ and __________, Cross: They require :

Answer 62

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

Question 63

In endocytosis, the cell takes in Endocytosis is a reversal of There are three types of endocytosis:

Answer 63

macromolecules by forming vesicles from the plasma membrane exocytosis, involving different proteins Phagocytosis (“cellular eating”) Pinocytosis (“cellular drinking”) Receptor-mediated endocytosis

Question 64

In Phagocytosis, a cell The vacuole fuses with a _________ to :

Answer 64

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

Question 65

In Pinocytosis, molecules are Pinocytosis is nonspecific for .... any and all solutes are Parts of the plasma membrane that form vesicles are

Answer 65

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

Question 66

In receptor-mediated endocytosis, vesicle formation is Receptor proteins bound to specific solutes from the extracellular fluid are Emptied receptors are

Answer 66

triggered by solute binding to receptors clustered in coated pits that form coated vesicles recycled to the plasma membrane by the same vesicle

Question 67

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

Answer 67

take in cholesterol low-density lipoproteins (LDLs)

Question 68

In exocytosis transport, Many secretory cells use exocytosis to For example, cells in the pancreas secrete insulin by exocytosis

Answer 68

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

Question 69

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

Answer 69

made up of a phospholipid bilayer sandwiched between two protein layers electron microscope pictures of membranes