Mitosis And Transport Across Membranes

Question 1

How is the cell cycle divided

Answer 1

Into interphase and mitosis

Question 2

What happens in interphase

Answer 2

• Cell carries out normal functions (e.g protein synthesis)
• time period between cell divisions

Question 3

How is interphase split up

Answer 3

• G1
• S phase
• G2

Question 4

What happens in G1

Answer 4

• protein synthesis begins
• vol of cytoplasm increases
• vol of organelles increase

Question 5

What happens in S phase

Answer 5

• Dna replication takes place
• his tone proteins are synthesised

Question 6

What happens in G2

Answer 6

• proteins required for cell division are synthesised
• energy stores accumulate
• chromosomes begin to condense prior to nuclear div

Question 7

What are the cell cycle check points

Answer 7

• G1 - is cell big enough, are there sufficient nutrients, are conditions in cell favourable
• G2 - has DNA replicated without mistakes, is the cell big enough
• metaphase - are chromosomes attached to the spindle properly

Question 8

What happens if checkpoints aren’t passed

Answer 8

The cell goes down apoptific pathway and self destructs

Question 9

How is cancer caused

Answer 9

Uncontrollable cell division to form tumours, cancer cell starts dividing without the usual ‘start signals’ and fail to stop at checkpoints if faults have occurred

Question 10

How do many cancer drugs work

Answer 10

Involve blocking some part of cell cycle to prevent uncontrolled division

Question 11

How is the rate if cell division controlled

Answer 11

Interaction of proto-oncogenes (promote normal cell div) and tumour suppressor genes (promote apoptosis)

Question 12

What is mitosis

Answer 12

Cell div for growth of organism and repair of tissues and replacement of cells

Question 13

What is stage one of mitosis

Answer 13

PROPHASE - chromosomes become visible as they shorten and thicken (condense), nuclear envelope breaks down, centrioles move to opposite poles of cell, spindle fibres start to form

Question 14

What is stage 2 of mitosis

Answer 14

METAPHASE - chromosomes can be seen as x shaped with 2 chromatids joined at centromere, chromosomes line up along the equator of the cell, chromosomes are attached to the spindle at the centromere

Question 15

What is stage 3 of mitosis

Answer 15

ANAPHASE - microtubules in the spindle contract, chromatids are pulled apart and move towards opposite poles of the cell

Question 16

What is stage 4 of mitosis

Answer 16

TELOPHASE - 2 groups of chromatids form 2 new nuclei, chromosomes uncoil, cytokinesis take place, new cells are genetically identical to each other and original cell

Question 17

What is binary fission and the process

Answer 17

Way prokaryotic cells reproduce :
1. Circular chromosome and plasmids replicate
2. Cell gets larger + dna moves to opposite ends of cell
3. Cytoplasm divides and new cell wall forms
Each have 1 copy of each of circular chromosomes but diff no of plasmids

Question 18

How quickly do prokaryotes divide by binary fission

Answer 18

In right environment (warm + lots of nutrients) every 20 min

Question 19

How else do bacteria divide

Answer 19

• transduction - genetic transfer from 1 bacteria to another through a virus
• transformation - a bacterium takes up a piece of DNA floating in its environment
• conjugation - one bacterium transfers genetic material through direct contact

Question 20

Describe viral replication

Answer 20

• hiv binds to receptor on helper T cells and is able to enter host cell
• reverse transcriptase catalyses use of viral RNA to form viral DNA
• intergrase enables the viral DNA to be intergrated into host genome
• new virons are assembled and bud out of new cell by exocytosis

Question 21

Phospholipids in fluid mosaic model

Answer 21

Form basic bilayer structure of membrane and act as a barrier to water soluble substances but allow passage of lipid soluble substances

Question 22

Glycolipids in fluid mosaic model

Answer 22

Play a key role in electrical insulation of cells and cell signalling

Question 23

Cholesterol in the fluid mosaic model

Answer 23

Regulates membrane fluidity and prevent lateral movement of phospholipid molecules

Question 24

Integral proteins in fluid mosaic model

Answer 24

• At least one part of molecule embedded within hydrophobic part of phospholipid bilayer
• hydrophobic R groups in contact with tails, hydrophilic R groups in contact with aqueous sol
• can’t be removed

Question 25

Peripheral proteins in fluid mosaic model

Answer 25

- don’t interact with hydrophobic part of phospholipid bilayer - can’t be removed

Question 26

Functions of protein in cell membranes

Answer 26

- transport - cell adhesions - enzymes - recognition

Question 27

How do proteins act as transports in cell membrane

Answer 27

Channel and carrier transmembrane proteins perform facilitated diff and active transport, diff protein channels and carriers give membrane key property of selective permeability

Question 28

How do membrane compartmentalise cells

Answer 28

Allow separation of substances within cells e.g hydrolytic enzymes within lysosomes

Question 29

How do proteins help in cell communication

Answer 29

Some transmembrane glycoproteins act as receptors for hormones and neurotransmitters, once hormone is bound it initiates a series of responses on the intracellular side

Question 30

How do proteins help in cell recognition

Answer 30

Glycoproteins on cell surface membranes act as identity markers allowing cells to recognise each other

Question 31

How do proteins help in cell adhesion

Answer 31

Glycoprotein on cell surface membrane hold adjacent cells together to form tissues

Question 32

What are the 3 factors that affect permeability

Answer 32

1. Heat —> kinetic energy - phospholipids in membrane move more - more permeable due to increased fluidity (larger gaps) - at high temp proteins denature so permeability increases 2. Ethanol —> organic solvent can dissolve lipids - phospholipids dissolve - disrupts structure - increase permeability 3. Ph —> denature proteins in membrane - increase permeability

Question 33

What does the substance have to be inorder to go through membrane

Answer 33

Has to be soluble in phospholipid bilayer e.g steroid hormones, o2 + co2 not glucose, protein, lipid, ions

Question 34

Simple diffusion

Answer 34

Random movement of molecules from high conc to low conc until dynamic equilibrium - passive

Question 35

What are the factors affecting simple diffusion

Answer 35

1. Inc no of particles = inc rate of diff 2. Inc mass of molecule = dec rate of diff 3. Inc temp = Inc rate of diff 4. Inc sa:v = Inc rate of diff (more space for molecules to move through) 5. Inc conc gradient = Inc rate of diff 6. Dec length of diff path = Inc rate of diff

Question 36

What is facilitated diffusion

Answer 36

- Allows substances that aren’t lipid soluble to be diffused - eg glucose + amino acids - helped by transport proteins in plasma membrane - channels allow molecules through + can be opened or shut, carriers allow molecules to bind to them and chances shape so molecule is passed through ( selective to specific molecule) - can become saturated as there is always a limited no of proteins available (simple can’t)

Question 37

What is active transport

Answer 37

- Movement of substances against a conc gradient requiring atp (used directly) - depends on proteins in cell membrane to transport specific molecules and ions - carriers can carry up to 2 in opposite directions

Question 38

Sodium potassium pump

Answer 38

- example of active transport (uses atp) - movement of potassium and sodium in opposite directions - used in co transport

Question 39

Describe co transport

Answer 39

- involves active transport, facilitated diff and co transport - e.g sucrose movement in glucose storing cells in plant: 1. Active transport of h+ ions out cell 2. Which builds a conc gradient of h+ outside the cell 3. Co transport proteins move h+ ions back into cell along conc gradient and sucrose against

Question 40

Example of co transports

Answer 40

Absorption of glucose/amino acids in the small intestine: - high conc of glucose in lumen: facilitated diff into epithelial cells + into blood - low conc of glucose in lumen : uses co transport- sodium potassium pump uses ATP to move na+ out of cell into blood to create a conc gradient between lumen and epithelial cell, sodium glucose co transporter uses conc gradient of na+ to move both na + and glucose into cell (glucose down conc gradient na+ with), facilitated diff of glucose into blood (conc gradient maintained as blood moves)

Question 41

What is bulk transport

Answer 41

- active processes to move large molecules in or out of cell - endocytosis : phagocytosis involves projections of cell membrane engulfing object which is contained in a vesicle, lysosome fuse with vesicle and release hydrolytic enzymes - exocytosis : transports molecules out of the cell - secretion

Question 42

Describe osmosis

Answer 42

- process to exchange water - molecules move from region of high water potential to region of low water potential through selectively permeable membrane - eg red blood cells in pure water swell and burst

Question 43

Water potential

Answer 43

- the pressure exerted by water molecules that are free to move in a system - pure water has a water potential of 0kPa - as you add solutes the water potential becomes more negative