6.1.1: cellular control

Question 1

what is a mutation?

Answer 1

change in the sequence of bases in dna

Question 2

how does substitution and insertion/deletion cause a gene mutation?

Answer 2

substitution
- changes codon (one base switched with a different one)
- if the new codon codes for a different amino acid = change in primary structure of the protein
- degenerate nature = could cause no mutations
insertion/deletion
- causes a frameshift mutation = move to either the left (deletion) or right (insertion)

Question 3

what are the effects of different mutations?

Answer 3

• no effect: normally functioning proteins are still synthesised
• damaging: proteins are no longer synthesised or proteins are non-functional = interfere with one or more essential processes
• beneficial: new and useful characteristic in the phenotype

Question 4

what are the 4 different ways genes can be regulated?

Answer 4

• trancriptional = genes can be turned on or off
• post-transcriptional = mrna can be modified which regulates translation and the types of protein produced
• translational = translation can be stopped or started
• post-translational = proteins can be modified after synthesis which changes their functions

Question 5

what are transcription factors?

Answer 5

• proteins that bind to specific dna sequences to initiate the transcription of genes into mrna
• when a genes is “switched off, transcription factors cannot bind to dna = prevents transcription

Question 6

what are the 2 forms that chromatin can exist in?

Answer 6

• heterochromatin: densely packed = difficult for rna polymerase to access genes, preventing transcription
• euchromatin: lossely packed = easy access for rna polymerase, enabling transcription

Question 7

why does histone modification occur?

Answer 7

dna coils around histones as they are positively charged while dna is negatively charged

Question 8

what are the histone modifications that promote transcription?

Answer 8

• acetylation: adding acetyl groups to histones = decreasing their positive charged = looser dna coil
• phosphorylation: adding phosphate groups to histones = reduces their positive charge = looker dna coil
  = increased transcription!

Question 9

what is a histone modification that inhibits transcription?

Answer 9

methylation: adding methyl groups to histones = increasinf hydropjobic interactions = tightening coil = reduces transcription

Question 10

how is mrna “edited” after transcription (post transcriptional control of gene expression)?

Answer 10

1) introns = don’t code for an amino acid vs exons = do code for amino acids
2) during transcription, they are both copied into mrna (called pre-mrna)
3) introns are removed from pre-mrna via splicing and exons joined = mature mrna
4) mature mrna leaves nucleus for translation

Question 11

what happens during post-translational control of genes?

Answer 11

• adding of non-protein groups
• folding and shortening of protein
• activation of cyclic amp (messenger molecule in cells as is often in the activation of enzymes)

Question 12

what are lac operon?

Answer 12

• group of 3 genes (lacz, lacy and laca) involved in the metabolism of lactose
• structural genes
• code forenzymes beta-galactosidase, lactose permease and transacetylase
  -transcribed onto a single long molecule of mrna

Question 13

what does the lac operon consist of?

Answer 13

• a promoter region (where rna polymerase binds)
• an operator region (where the repressor protein binds to)
• structural genes lac yza
• regulatory gene lac l a short distance away

Question 14

what happens in lac operon when there is an absence of lactose?

Answer 14

• repressor protein binds to operator region
• prevents rna polymerase from binding to the promoter
• blocks transcription, meaning genes xyz cannot be expressed, resources not waster

Question 15

what happens in the presence of lactose?

Answer 15

• lactose binds to repressor protein
• changes it shape, so can no longer bind to operator region
• means that rna polymerase can bind to the promoter region and begin transcription

Question 16

what are homeobox genes sequences?

Answer 16

• are similar and highly conserved in plants, animals and fungi
• involved in regulating gene expression

Question 17

what are hox genes?

Answer 17

particular types of homeobox genes only found in animals

Question 18

what is apoptosis?

Answer 18

“programmed cell death”, where some cells break down as part of the normal development of an organism

Question 19

what are the sequence of events for apoptosis?

Answer 19

1) enzymes break down cell cytoskeleton
2) cytoplasm becomes dense with tightly packed organelles
3) cell surface membrane changes and blebs form
4) chromatin condenses, the nuclear envelop breaks and dna breaks
5) cell breaks into vesicles = ingested by phagocytic cells, so that cell debris does not damage any other cells or tissues

Question 20

what are 3 examples of internal stimuli that can affect apoptosis?

Answer 20

• dna damage
• hormones
• cytokines from immune system

Question 21

what are 3 examples of external stimuli that can affect apoptosis?

Answer 21

• infections by pathogens
• changes in temperature
• changes in light intensity