cell divison Flashcards
1
Q
what are the main components of interphase?
A
Gap 0 - resting phase, for cells not dividing
Gap 1 - cell grows, new organelles, protein and mRNA made
Synthesis - DNA replication, 2N —> 4N for mitosis
Gap 2 - cell grows, new organelles, proteins and mRNA made
2
Q
explain what occurs during prophase in mitosis
A
- chromosomes condense, becomes short and fat
- becomes visible under microscopes
- X-shaped chromosomes, joined by centromere, sister chromatids identical
- centrioles moves to poles of cell
- prometaphase —> nuclear envelope starts to break down to release chromosomes into cytoplasm
3
Q
explain what occurs during metaphase in mitosis
A
- chromosomes line up along by centre/equator of the cell attached to the mitotic spindle by their centromeres
- arranged sideways and neatly
4
Q
explain what occurs during anaphase in mitosis
A
- spindle fibres contract, pulling sister chromatids away from each other, towards the poles
- centromeres are pulled first causing them to look v-shaped + 2 separate groups of chromatids
5
Q
explain what occurs during telophase in mitosis
A
- chromatids each the poles uncoil and become long and thin again
- new nuclear envelope from around 2 new full sets of chromosomes forms 2 new nuclei, daughter nuclei - genetically identical
6
Q
explain what occurs during cytokinesis
A
- when cell physically separates and cytoplasm splits, contractile ring forms at centre that makes an indentation called cleavage furrow
- pinches in and the cell divides into 2 identical daughter cells —> starts in telophase
7
Q
what is the difference between mitosis and cancer?
A
- mitosis is a controlled process of cell division but cancer is the uncontrolled division
8
Q
describe the difference between malignant and benign tumours
A
- malignant tumour grows rapidly and can invade healthy neighbouring tissues but benign tumour grows slowly and does not spread
9
Q
what’s the purpose of cancer treatments?
A
- control the rate of cell division in tumour cells by disrupting the cell cycle and killing tumour cells - kill as they divide more frequently
10
Q
explain the role of chemotherapy?
A
- prevents synthesis of enzymes needed for DNA replication in gap phase 1, cell cannot enter synthesis phase
- disrupting cell cycle and cause the cell to kill itself
11
Q
explain the role of radiation therapy
A
- radiation damages DNA in the synthesis phase - if severe damage detected, cell kills itself, preventing further tumour growth
12
Q
explain the steps in cell division in prokaryotes - binary fission
A
1) circular DNA and plasmids replicate 9once for circular, more for plasmids)
2) cell gets bigger and DNA loops move to opposite poles of the cell
3) cytoplasm begins to divide and new cell walls begin to form
4) cytoplasm fully splits and 2 daughter cells made, each with one identical loop of circular DNA and with variable plasmids
13
Q
explain the steps in viral replication
A
1) attach to host cell using their attachment proteins which bind to complementary receptor proteins on surface membrane of host cell
2) genetic material from virus released into host cell
3) host cell’s ‘machinery’ like enzymes/ribosomes to replicate genetic material and proteins
4) viral components assemble inside host cell. Replicated viruses released from host cell
14
Q
describe the function of cell membranes
A
- surrounds cells
- barrier between cell and environment
- regulates movements of substances into/out of cell
- partially permeable
15
Q
describe the function of membranes within cells
A
- divides cell into compartments
- surrounds organelles
- mitochondria - membrane permeable to respiration substances
- nucleus - RNA leaves by pores in membrane
- partially permeable
16
Q
what are the components in membrane
A
- phospholipids
- cholesterol
- glycolipids
- glycoproteins
- proteins
17
Q
explain the structure and function of the phospholipid bilayer
A
- polar, charged heads are hydrophilic (attracts water) but non-polar, uncharged fatty acid tails are hydrophobic (repels water)
- naturally arranged with heads facing aq environments, shielding tails
18
Q
How does the bilayer structure aid function?
A
- hydrophobic molecules can pass through as they do not repel the fatty acid tails
- small molecules can fit between phospholipids
- polar ions are water soluble so cannot pass through on their own as they repel the fatty acids and tails
- electrical insulators as charged molecules cannot pass through
19
Q
Describe the structure of cholesterol in the membrane
A
- type of lipid
- in all cell membranes
- fit between the phospholipids
- bind to hydrophobic tails mainly non-polar
- causes tails to pack closely together become more rigid. Less fluid
20
Q
Explain the main functions of cholesterol in the membrane
A
- maintains fluidity, stability and strength of membranes
- restricts movement of phospholipids
- reduce lateral movement of molecules + phospholipids
- makes membrane less fluid at high temperature to prevent damage
- prevents loss of water and dissolved ions as tails hydrophobic and closer together
21
Q
Describe the structure of glycolipids in membranes
A
- polysaccharide chain, covalently bonded with a lipid
- extends from the bilayer into aq environment
22
Q
Explain the functions of glycolipids in membrane
A
- helps cells attach together to form tissues
- recognition sites, maintains stability of membranes
- cell-surface receptor sites
23
Q
Describe the structure of glycoproteins
A
- polysaccharide chain bonded to an extrinsic protein + extends from the bilayer into aq environment
24
Q
Explain the functions of glycoproteins
A
- allows cells to recognise each other (e.g: lymphocytes as own cells)
- helps cells attach together to form tissues
- recognition sites
25
what are the different types of proteins?
- intrinsic/integral
—> channel and carrier proteins
- extrinsic/ peripheral
26
What is the difference between intrinsic and extrinsic proteins?
Intrinsic proteins:
- hydrophobic amino acids on outside that interact with tails inside.
- transmembrane + transport function
Extrinsic proteins:
- on the surface + the structural role is that enzymes, receptors, detect chemicals
27
Explain the structure and function of protein channels
- forms pores in membrane which charged particles diffuse through
- has central pore, lined with hydrophilic amino acids and filled with water
- selective + diff proteins channels facilitate diffusion of different charged particles so only some chemicals can pass through
28
Explain the structure and function of protein carriers
- move large molecules across the membrane
- specific large molecule attaches to a specific binding site on carrier protein in membrane
- the protein changes shape due to its tertiary structure altered to release the molecule on opposite side of the membrane
29
Fluid mosaic model
Fluid
- individual phospholipids can move past each other
- flexible structure constantly moving and changing shape due
- moves but never exposes fatty acid tails and stable due to cholesterol.
Mosaic
- proteins, glycoproteins + glycolipids in bilayer vary in shape and size
- creates a mosaic-like pattern from above
30
How does temperature at 0 degrees affect phospholipid permeability?
- phospholipids do not have much energy so can’t move very much
- packed closely together, rigid, channel and carrier proteins denature
- permeability is high
- ice crystals may pierce the membrane when they thaw
31
How does temperature at 0-45 degrees affect phospholipid permeability?
- lowest permeability at 0 degrees - proteins not denatured but rigid structure
- phospholipids gain kinetic energy as temp increases
- move more and not packed tightly
- as temp increases permeability increases
32
How does temperature at 45 degrees affect phospholipid permeability?
- damage to cell surface membranes
- proteins denature and can’t control what enters or leaves
- water inside cell expands and puts pressure on membrane and damages it
- increases fluidity and damage to phospholipid bilayer
33
Explain what is meant by simple diffusion
- the net movement of particles from a region of high region of low concentration, down the conc gradient through a partially permeable membrane. - passive process
- simple diffusion —> molecules diffuse directly through membrane
34
What can go through membrane by simple diffusion and why?
- particles that move freely though a membrane can diffuse through it - able to flow and have kinetic energy
- gases - oxygen + CO2 diffuse into and out of cell respiration
- hydrophobic molecules - don’t repel from hydrophobic fatty acid tails
35
How does concentration gradient affect rate of simple diffusion
- greater = faster
- as diffusion takes place, conc difference reduced unit equilibrium so diffusion slows down until its reached
36
How does surface area affect rate of simple diffusion?
- greater = faster
- more area is exposed for particles to use and diffuse through
37
How does distance affect rate of simple diffusion
Shorter = faster
- particles have less distance to cover
38
How does temperature affect rate of simple diffusion
Warmer faster
- more kinetic energy, move faster
39
What are some examples of efficient diffusion
Lungs - alveoli:
- thin exchange surface - 1 cell thick
- large SA
- steep conc gradient of O2 and CO2
O2 moves alveoli —> blood
CO2 moves blood —> alveoli
Small intestine - microvilli:
- microvilli on epithelial cells provide 600X SA
- thin walls
- steep conc gradient
40
What are the limitations imposed by the phospholipid bilayer
- only certain molecules can pass through the phospholipid bilayer
- made of phospholipids which is polar, hydrophilic head and nonpolar, hydrophobic fatty acid tails shielded by heads
- arranges close in fluid mosaic model - allows small molecules to pass through
41
Explain what is meant by facilitated diffusion?
- the passive net movement of particles across cell membrane from area of high conc to an area of low concentration, down conc gradient by means of a transport protein located in the cell membrane
- integral, transmembrane proteins to transport molecules through membrane in protein channels and carrier proteins.
42
What can pass through by facilitated diffusion?
- larger molecules like glucose and amino acids
- charged/polar/hydrophilic molecules
- water soluble molecules
- molecules that readily pass through cell membrane via simple diffusion
43
Factors affecting rate of facilitated diffusion
Conc gradient
- greater = faster
- up to a point if all proteins are in use. As equilibrium reaches, rate plateaus
No. Proteins channel/carriers
- more = faster
- once all in use, the rate of diffusion cannot increase even if other factors increase
44
Explain what is meant by osmosis
- the movement of water from area of higher water potential (less negative) to an area of lower water potential over a partially permeable membrane. - passive process + doesn’t require metabolic energy/ATP
45
What are aquaporins?
- special types of protein channels that allow the facilitated diffusion of water through cell membranes. Kidney cells adapted to have lots of them to help reabsorption of water
46
Define what the term ‘water potential’ refers to
- water potential is the likelihood of water molecules to diffuse out of or into a solution
- pure water is 0. Can’t get a water potential higher than 0
- adding solute lowers water potential, making more negative. More conc solution more negative with more solute
—> high water potential in hypotonic
—>lower water potential in hypertonic
Water moves from hypotonic —> hypertonic
47
Describe the types of solutions
- hypotonic - water potential is higher (closer to 0) than water potential of cell
- isotonic - water potential same inside and outside cell
- hypertonic - water potential of solution is lower (move -ve) than water potential of cell membranes
48
How does the water potential gradient affect rate of osmosis?
Higher gradient = faster
- as osmosis takes place, the difference in water potential on either side of membrane decreases, so rate of osmosis levels off over time
49
How does thickness of exchange surface affect rate of osmosis?
Thinner = faster
- shorter distance for the water molecules to travel
50
How does surface area of exchange surfaces affect rate of osmosis
Larger = faster
- more area for the water molecules to travel through in set amount of time
51
Explain what is meant by ‘active transport’
- movement of substances from an area of low concentration to an area of high concentration, against the concentration gradient, requiring energy from ATP and carrier proteins
52
Describe the processes of active transport
1) a molecule binds to receptor complementary to its shape on carrier protein. Each carrier protein specific and only transport one type of ion
2) ATP binds to carrier protein from inside of cell.
3) ATP hydrolysed into ADP and Pi
4) Pi attached to protein causing phosphorylation
5) produces conformational change of protein in tertiary structure so molecule released on other side of membrane
6) carrier protein returns original shape when inorganic phosphate ions released after molecule transported
53
Co-transport meaning
- transport of 2 molecules, one going down conc gradient and one against conc gradient. Energy for active transport indirectly from conc gradient of other molecule
54
What’s the difference between symposium and antiport?
- symport —> if 2 molecules transported in same direction. Sodium-glucose cotransporter
- antiport —> if 2 molecules transported in opposite directions. Sodium-calcium exchangers
55
56
Explain the glucose absorption in the ileum (ileum —>epithelial cells —> capillary)
1) high concentration of glucose in ileum following digestion. Low conc glucose in epithelial cells lining ileum
2) glucose can enter by facilitated diffusion by carrier proteins
3) rate of facilitated diffusions slows as conc gradient falls —> can’t absorb glucose by facilitated diffusion so glucose absorbed by active transport
57
Explain what occurs during the sodium potassium pump (carrier proteins between bloodstream + epithelial cell)
1) Na+ from epithelial cell —> bloodstream by active transport indirectly sodium potassium pump
—> K+ from blood = epithelial cells
2) as ileum has high concentration of Na+ ions following digestion, conc of Na+ ions now lower in epithelial cels than ileum, creates conc gradient between lumen of ileum and epithelial cells
58
What occurs during the sodium glucose co-transport
1) Na+ ions into epithelial cells form ileum via facilitated diffusion down conc gradient - attaches to complementary shape receptor
2) in same co-transporter, glucose attaches to it and absorbed into epithelial cells, against its conc gradient
3) Na+ released on other side - enables glucose be released. Transported together
4) glucose absorbed by active transport indirectly- glucose absorbed fast rate
5) energy for active transport of glucose - indirectly from conc gradient of Na+ ion
6) glucose enters bloodstream by facilitated diffusions slows
