4: Transport across cell membranes

Question 1

What is plasma membrane?

Answer 1

All membranes around and within all cells

All have the same basic structure

Question 2

What does the cell-surface membrane do?

Answer 2

Allows different conditions in and out of the cell
Controls the movement of substances
Provides structural integrity

Question 3

How are phospholipids essential for cell-surface membranes?

Answer 3

Hydrophillic heads point towards outside of the cell as attracted by water on both sides
Hydrophobic tails point to the center of the cell membrane, repelled by water

Question 4

What does amphiphatic mean?

Answer 4

Contains both hydrophobic and hydrophillic components

Question 5

Why is a membrane said to be a fluid mosaic?

Answer 5

Fluid: flows, moves, changes shape
Mosaic: different size, patterns, shapes

Question 6

Why does the cell-surface membrane have pores?

Answer 6

Selectively permeable

Question 7

What types of proteins exist in the cell-surface membrane?

Answer 7

Intrinsic/integral/transmembrane

Extrinsic/peripheral

Question 8

What is an intrinsic protein?

Answer 8

Span the full bilayer from one side to the other
They interact with the lipophillic core and it embeds them there
Protein channels / Carrier proteins

Question 9

What is a protein channel?

Answer 9

Water filled tubes to allow water-soluble ions to diffuse across the membrane

Question 10

What is a carrier protein?

Answer 10

Binds to ions or molecules (glucose/amino acids)
Causes a change in conformational shape
Moves the molecule across the membrane

Question 11

What are the function of proteins in the bilayer?

Answer 11

Structural support
Acts as channels transferring water-soluble substances
Allows active transport using carrier proteins
Cell-surface receptors for identifying cells
Helps cells adhere (join) together
Acts as receptors (hormones)

Question 12

What is an extrinsic protein?

Answer 12

Surface of bilayer, never extends beyond

Question 13

What are the functions of extrinsic proteins?

Answer 13

Mechanical support
Cell receptors with glycolipids
Cell receptors for hormones

Question 14

Where is cholestrol found?

Answer 14

Within the bilayer

Question 15

What does cholestrol do in the bilayer?

Answer 15

Provides strength to membrane
Reduce lateral movement of molecules
Make the membrane less fluid at high temp
Prevent leakage of water and dissolved ions

Question 16

What is a glycolipid?

Answer 16

Carbohydrate covalently bonded to a lipid

Carb. extends outside the cell

Question 17

What is the function of glycolipids?

Answer 17

Recognition sites (ABO Blood)
Maintain stability of membrane
Helps cells to attach to each other

Question 18

What is a glycoprotein?

Answer 18

Carbohydrate chains bonded to extrinsic protein

Question 19

What are the functions of glycoproteins?

Answer 19

Recognition sites
Help cells attach to each other
Recognition (e.g lymphocytes recognise own cells)

Question 20

When is transport across the bilayer not possible?

Answer 20

Molecules not lipophillic
Too large to pass through channels
Same charge as proteins
Polar (electrically charged) therefore cannot move through the non-polar hydrophobic tails

Question 21

What are the functions of intracellular membranes?

Answer 21

Divides cytoplasm from organelle contents
Entry and exit 
Internal transport mechanisms 
Enzyme isolation
Interface for reactions

Question 22

How can a rate of entry graph differ with facilitated diffusion and diffusion?

Answer 22

Facilitated diffusion graph plateaus as the channel protein becomes saturated

Question 23

What are similarities between how H2O and O2 diffuse?

Answer 23

Move down conc. gradient

Diffuses through phospholipid bilayer

Question 24

Why does the rate of uptake increase in the presence of oxygen?

Answer 24

Active transport - using O2 creates ATP energy to cause the carrier proteins to change shape

Question 25

Why does uptake of a substance increases as conc. does?

Answer 25

Diffusion is proportional to conc. gradient

Question 26

What are the things that hold chromatids together?

Answer 26

Centromere

Question 27

How many chromosomes found in nuclei in telophase and a sperm cell if there are 26 in prophase?

Answer 27

Prophase: 26 Telophase: 26 Sperm cell: 13

Question 28

How much mass of DNA found in nuclei in telophase and a sperm cell if there is 60 in prophase?

Answer 28

Mass of DNA in Prophase: 60 Telophase: 30 Sperm cell: 15

Question 29

How does faulty DNA cause cancer?

Answer 29

Protein is faulty / not made Cells with faulty DNA divide Uncontrolled division

Question 30

A cancer drug that stops spindle fibers shortening would stop what stage?

Answer 30

Anaphase

Question 31

Explain diffusion

Answer 31

Net movement of molecules or ions from a region of higher to lower concentration until even distribution

Question 32

How does kinetic energy affect particles?

Answer 32

All particles are constantly in motion due to kinetic energy Motion is random Particles constantly bounce off each other as well as other objects

Question 33

What is required for facilitated diffusion?

Answer 33

Trans-membrane channels and carriers

Question 34

Is facilitated diffusion require energy?

Answer 34

No, it is passive

Question 35

How are protein channels selective?

Answer 35

Each opens in the presence of a specific ion | Ion binds with protein causing it to change shape and opens one side and close the other

Question 36

What causes the particles to move in facilitated diffusion?

Answer 36

Kinetic energy of the molecules

Question 37

Define osmosis

Answer 37

Passage of water from region of high to low water potential through a selectively permeable membrane

Question 38

What is water potential (Ψ)?

Answer 38

Pressure created by water molecules (kPa)

Question 39

What is water potential of pure water under standard conditions?

Answer 39

0

Question 40

What are "standard conditions" for Ψ?

Answer 40

25C and 100 kPa of pressure

Question 41

How does adding solute affect Ψ?

Answer 41

Lowers water potential | Therefore any solutions Ψ must be negative

Question 42

How is water potential affected as a solution becomes more concentrated?

Answer 42

As concentration increases the Ψ becomes more negative

Question 43

How could you find the Ψ of cells?

Answer 43

Place them in a series of solutions with different Ψ | Where there's no net change of water, the Ψ must be equal to the solution

Question 44

Does osmosis require energy?

Answer 44

Only requires kinetic energy of the water molecules

Question 45

Why does a partially permeable membrane not allow solute molecules?

Answer 45

They are too big to fit through the pores

Question 46

What is an isotonic solution?

Answer 46

A solution where the Ψ is the same as the cell

Question 47

What is a hypertonic solution?

Answer 47

A solution where the Ψ is lower than that in the cell | Hyper - high SOLUTE

Question 48

What is a hypotonic solution?

Answer 48

A solution where the Ψ is higher than that in a cell | Hypo - low SOLUTE

Question 49

What are the principles of exchange to increase exchange?

Answer 49

High SA:V ratio Thin layer Selectively permeable Movement of the external & internal environment

Question 50

How does a high SA:V ratio affect exchange?

Answer 50

Increases rate of exchange - as increased frequency of collision with exchange surface

Question 51

How does a thin layer affect exchange?

Answer 51

Short diffusion pathway length | Quicker transport through membranes

Question 52

What is villi?

Answer 52

1mm in length which is folded to increase SA

Question 53

What is microvilli?

Answer 53

600nm in length | Found on enterocyte border

Question 54

What is an enterocyte?

Answer 54

Cell of the intestinal lining

Question 55

What is the purpose of the circularity systems?

Answer 55

Maintains concentration gradients

Question 56

What occurs when cells are placed in a hypertonic solution?

Answer 56

Plant cells tissue flaccid & plasmolysis | Animal cells shrink (RBC crenation)

Question 57

What occurs when cells are placed in a hypotonic solution?

Answer 57

Animal cells burst (cytolysis) & RBC undergo haemolysis | Plant cells become turgid

Question 58

Define active transport

Answer 58

Movement of molecules/ions from low to high conc. using ATP and carrier proteins

Question 59

How does active transport affect net movement?

Answer 59

No equilibrium reached

Question 60

How selective is active transport?

Answer 60

Highly selective

Question 61

Explain the process of active transport

Answer 61

Molecule/ion binds to carrier protein ATP attaches to protein and phosphorylation occurs and causes conformational change Opens to opposite side of the membrane and molecule/ion released

Question 62

What is the phosphorylation?

Answer 62

ATP ADP + Phosphorus

Question 63

Explain the process of a sodium-potassium pump?

Answer 63

3 Na+ binds to binding site Phosphorylation occurs (ATP -> ADP + P) Conformational change in shape and Na+ released 2 K+ ions bind to protein and dephosphorylation causes change (P dissociates) 2 K+ ions released and process repeats

Question 64

What is direct/primary active transport?

Answer 64

Ions/molecules pumped against conc. gradient

Question 65

What is indirect/secondary active transport?

Answer 65

Conc. gradient generated by ion pump, then co-transport of ion with chemical

Question 66

What is co-transport?

Answer 66

A molecule is transported against conc. gradient with another substance down the conc. gradient

Question 67

Describe the co-transport in the enterocyte?

Answer 67

Direct active transport causes Na+ to go to blood and K+ ions to diffuse into cell (Na-K pump) Indirect active transport (co-transport) glucose binds to Na+ which moves down conc. gradient Facilitated diffusion of glucose from enterocyte to bloodstream

Question 68

What is the effect of an isotonic solution?

Answer 68

No affect on animal cells | Incipient plasmolysis in plant cells

Question 69

What is incipient plasmolysis?

Answer 69

When the protoplast is just about to pull away from cell wall