chromosomes, cell structure + regulation

Question 1

chromatin

Answer 1

chromosomal DNA forms complex with RNA and proteins

Question 2

DNA packing

Answer 2

DNA helix -> nucleosome beads-packed around histones -> nucleosome packing -> extended chromosome -> chromosome packing -> supercoiled chromosome

Question 3

heterochromatin

Answer 3

more condensed and densely staining. found near nuclear envelope, represents switched off genes. 2 types: constitutive and facultative

Question 4

euchromatin

Answer 4

less condensed and lightly staining. represents genes which are switched on [being expressed]. more central location

Question 5

chromosome structure

Answer 5

• chromatin is packed into bead-like structures called nucleosomes
• each nucleosome comprises of 2 loops of DNA wrapped around a cluster of 8 histones
• chromosomes form from the supercoiling and condensation of chromatin
• genes are specialised functional sites arranged along the chromosome

Question 6

histones

Answer 6

rich in basic amino acids eg, lysine and arginine. core histones are H2A, H2B, H3, H4.
linker histones are H1 and H5.
important in compacting DNA and chromatin regulation

Question 7

groups of diff. tissues in the groups depending on rates of cell turnover

Answer 7

1) continuously renewing- epidermis of skin, intestinal epithelium
2) conditionally renewing- liver, kidney, endocrine glands
3) non proliferate- cardiac, nerve cells

Question 8

cyclins and cyclin-dependant kinases [CDKs]

Answer 8

• regulatory molecules
• activate CDKs
• cell cycle can’t go backwards
• cyclins are made and degraded cyclically
• these proteins coordinate the cells entry into the next phase of the cell cycle

Question 9

cell cycle progression, regulated by cyclin-CDK complex

Answer 9

• CDKs become activated upon binding with cyclin.
• activated CDKs cause phosphorylation to activate/inactivate target proteins
• these proteins coordinate the cells entry into the next stage of the cell cycle

Question 10

cell cycle checkpoints

Answer 10

if a checkpoint fails it can lead to cancer- uncontrolled cell proliferation

Question 11

proto-oncogene

Answer 11

a normal gene which when altered by mutation, becomes an oncogene which can contribute to cancer. some proto-oncogenes provide cell signals that lead to cell division

Question 12

inhibitors of cyclin-CDK complexes

Answer 12

tumor suppressants. 2 families; the cip/kip family- halts the progression of the cell cycle