6.1.1 Cellular Control

Question 1

what’s a gene?

Answer 1

section of a DNA that codes for a polypeptide

Question 2

what’s a mutation?

Answer 2

change to the DNA bases/nucleotide

Question 3

what are the types of gene mutations?

Answer 3

• substitution
• insertion - one or more bases added to sequence of gene
• deletion - one or more bases removed from sequence of gene

Question 4

what’s the three types of substitution mutation?

Answer 4

• missense
• silent
• nonsense..

Question 5

what are effects of insertions/deletions?

Answer 5

• frameshift
• every codon after mutation is affected
• protein will have a different sequence of amino acids
• protein will have a different tertiary structure

Question 6

what is missense?

Answer 6

• where substitution causes one different amino acid to be coded for
• may change the proteins tertiary structure and overall 3D shape

Question 7

what’s nonsense?

Answer 7

• one base is substituted and causes a stop codon to be created
• shorter polypeptide produced and chain folds differently
• proteins functionality changes

Question 8

what’s silent?

Answer 8

• substitution occurs and has no effect on amino acid coded
• because of degenerate nature

Question 9

what’s Lac operon?

Answer 9

• happens in E. coli
• genes that produce enzymes needed to respire lactose when glucose isn’t available

Question 10

what’s the structure of the Lac operon when lactose isn’t present?

Answer 10

• repressor protein (regulatory gene’s product) switches off the other genes in sequence (P,O)
• P,O is where RNA polymerase binds to so transcription of X,Y cant happen
• product of structural genes (X,Y) makes enzymes, B galactosidase

Question 11

what’s the structure of the Lac operon when lactose is present?

Answer 11

• lactose binds to the repressor protein when present
• repressor protein changes shape
• this stops the repressor protein from binding to the operator (O) and promotor (P)
• RNA polymerase can now bind to P
• structural enzymes like lactase polymerase can now be transcribed

Question 12

what’s splicing?

Answer 12

• post transcriptional level
• mRNA modified by removing introns (non coding regions) to produce mature mRNA
• activated by cAMP

Question 13

what happens at the post translational level?

Answer 13

• some proteins require activation by molecules like hormones
• 1st/2nd messenger model used and molecules bind to cell membrane and trigger production of cAMP inside cell
• cAMP activates protein inside cell by altering their 3D structure (eg by changing active site to increase activity)
• activates enzymes BY PHOSPHORYLATION

Question 14

what’s a homeobox sequence?

Answer 14

• group of regulatory genes that cover a section of DNA for 180 base pairs (60 codons)
• codes for the protein homeodomain
• highly conserved (unaffected by evolution) in plants, animals and fungi

Question 15

whats the function of the protein homeodomain?

Answer 15

• binds to DNA to switch genes on and off
• control body plan (general structure of an organism)

Question 16

what are hox genes?

Answer 16

• a group of homeobox genes responsible for the position of body parts
• more complex organism means more clusters of hox genes

Question 17

what does an order of hox genes determine?

Answer 17

• head-tail orientation
• segments
• position of limbs and eyes

Question 18

what’s apoptosis?

Answer 18

programmed cell death

Question 19

what are the stages of apoptosis?

Answer 19

1. transcription factors made by hox genes cause cytoskeleton to be broken down by lysosomes
2. ’blebs’ form due to changes in the cell surface membrane
3. cells break off in fragments which are then digested by phagocytes to prevent harmful substances reacting w other cells

Question 20

what are two types of stimuli?

Answer 20

internal and external