PAPER 3 SYNOPTICS

Question 1

describe the structure of centrioles, and explain their role in cell division.
(CH2/6)

Answer 1

composed of microtubules in a 9+2 arrangement
- prophase: centrioles aid the formation of spindle fibres
- metaphase: the spindle fibres attach to the centrioles
- anaphase: the centrioles pull the spindle fibres (which are attached to the chromatids) and pull the spindles and chromatids to opposite poles
- telophase: the spindle fibres disappear, no longer attached to the centrioles
2 centrioles form a centrosome

Question 2

explain how chromosomes are formed.
distinguish heterochromatin and euchromatin.
(CH2/19)

Answer 2

• DNA wraps around histones (proteins) to form chromatin.
• The chromatin coils and condenses to form a chromosome
  1. heterochromatin: tightly wound DNA, its DNA cannot be transcribed
  2. euchromatin: loosely wound DNA, in which DNA can be transcribed

Question 3

outline the components of the cytoskeleton, the function of each component.
Explain the role of the cytoskeleton during cytokinesis in animal cells.
(CH2/6)

Answer 3

microfilaments: responsible for cell movement
microtubules: determine the shape of the cell
intermediate fibres: provide mechanical strength in cytoskeleton

the cytoskeleton pulls the cleavage furrow inwards during cytokinesis, dividing the cell into 2.

Question 4

explain the structure and function of lysosomes.
(CH2/12)

Answer 4

vesicles containing digestive enzymes
role in phagocytosis:
- phagocyte engulfs the pathogen after being attracted to it by chemicals released by the pathogen
- phagocyte encloses pathogen in to form phagosome
- lysosome combines with phagosome to form phaglosome
- digestive enzymes in lysosome digest and destroy pathogen

Question 5

outline the structure of the mitochondria, and its role in respiration.
- 4 points on structure
- 3 points on application of function to structure
(CH2/18)

Answer 5

• double membrane: inner foldings (cristae) with matrix (fluid) in the centre
• cristae are folded structures forming inner membrane
  —-> increase surface area for oxidative phosphorylation
• matrix contains enzymes:
  ——> required for krebs cycle & Link R
• inner mitochondrial membrane contains ETC’s and ATP synthase
  ——> plays role in movement of electrons down ETC and formation of ATP by pumping of H ions across membrane

Question 6

outline the structure of ribosomes, and explain their role in protein synthesis.
(CH2/3)

Answer 6

sometimes attached to RER.
- can be 70S(in prokaryotic cells) or 80S(in eukaryotic cells)
- site of protein synthesis:
->transcription: formation of mRNA molecule, DNA helicase unzips DNA, free RNA nucleotides pair with comp bases on antisense strand, form phosphodiester bonds catalysed by RNA polymerase. produces short strand of RNA referred to as mRNA, mRNA leaves nucleus
-> translation: mRNA attaches to ribosome to be translated, tRNA mol with complementary anticodon to mRNA codon binds, carrying an amino acid, peptidyl transferase catalyses formation of peptide bonds between adjacent amino acids

Question 7

outline the structure of chloroplasts, and their role in photosynthesis
(CH2/17)
(6 points)

Answer 7

• double membrane
• inner membranes- thylakoid
• stacked thylakoid membranes are called grana
• grana linked together my lamellae (thin pieces of thylakoid membrane)
• the light dependant stage of photosynthesis takes place in the thylakoid membrane
• the light independent stage takes place in the stroma

Question 8

explain the structure of a plasma membrane, linking the components to their functions.
(CH2/5)
(8 components, + their role)

Answer 8

• mainly formed from phospholipid bilayer: hydrophilic head/hydrophobic tails
• controls entrance and exit of molecules
• cholestrol: regulates fluidity
• intrinsic proteins; channel and carrier proteins
• extrinsic proteins
• glycoproteins: intrinsic proteins with attached carbohydrate chains
• glycolipids: lipids with attached carbohydrate chains, role in cell recognition