genetics 6

Question 1

where does mRNA transcription start

Answer 1

transcription start site

Question 2

what is the pribnow box essential for

Answer 2

transcription initiation

Question 3

what is the 35 region used for

Answer 3

high transcription rate

Question 4

what is prokaryotic genes regulated by

Answer 4

• promotor
• operator
• enhancers
• silencers

Question 5

what can related genes be arranged by

Answer 5

operons

Question 6

what does polycistronic mean

Answer 6

multiple protein encoding regions in a single mRNA

Question 7

what does the TATA box do

Answer 7

• in many eukaryotic promotors
• TATA binding proteins

Question 8

what does the CAAT box do

Answer 8

• site for CAAT-enhanced binding proteins

Question 9

what do introns almost always have

Answer 9

• begin with GU
• end with AG

Question 10

what is the characteristics of bacterial chromosomes

Answer 10

• large - 3.6-3.9 million
• circular DNA molecules
• nucleoid - where most DNA resides, has nucleoid associated proteins and domains (supercoiled loops)

Question 11

what are the characteristics of bacterial plasmids

Answer 11

• small (160,000- 1.8 million base pairs)
• circular DNA molecules
• separated from chromosomal DNA
• replicate independently
• supercoiled

Question 12

what are bacterial plasmids genes for

Answer 12

• antibiotic resistance
• horizontal transfer

Question 13

what % of components make up DNA

Answer 13

• 75% genome
• 1-2% encodes proteins - exons
• rest is introns and intergenic

Question 14

what are the types of DNA repeats

Answer 14

• dispersed repetitive DNA
• satelite DNA - repeats cluster together
• tandem repeats

Question 15

what are transposable elements and what are the forms

Answer 15

• type of dispersed repeat
• short interspersed elements (SINE’s) - 90-500 bp
• long interspersed elements (LINE’S) - up to 7000bp

Question 16

what are alpha satellite DNA repeats

Answer 16

• 171bp repeats
• 10% of the genome
• all centromeres
• high order repeat units (HORs)

Question 17

what do high order repeats do in satellite DNA repeats

Answer 17

HOR arrangement —-> chromosome specificty
- transcribed and large protein transcriptome

Question 18

what does VNTRs stand for

Answer 18

variable number of tandem repeats

Question 19

what are minisatellite repeats

Answer 19

• 10-60bp
• repeated 5-50 times
• GC rich - 3hb so much stronger
• many parts of genome
• centromeres and sub telomeric regions
• genetic fingerprinting

Question 20

what are microsatellite repeats

Answer 20

• short tandem repeats or simple sequence repeats
• <10bp repeats
• repeated 5-50 times
• telomeres - humans

Question 21

what are transposable elements

Answer 21

• DNA sequences that can change its position within a genome

Question 22

what do short interspersed elements do - SINE’s

Answer 22

• 90 to 500bp
• Alu repeats - contains Alu restriction sites
• adenine rich tail
• insertions —-> many diseases

Question 23

what do long interspersed elements do - LINE’s

Answer 23

• up to 7000bp
• adenine rich 3’ tail

Question 24

what do LTR- retrotransposons do

Answer 24

• gag gene expression —> virus like particles
• reverse transcriptase of RNA to cDNA
• integration into genome
• requires intergrase

Question 25

what do transposons do

Answer 25

• variable in size
• contain transposae gene
• tandem inverted repeats
• short tandem site duplication

Question 26

what is the structure of nucleosomes

Answer 26

• 146 bp around histone
• 8 histone protein
• 2 x H2A, H2B, H3, H4
• 20-60 bp spacer

Question 27

what is the structure of chromatosomes

Answer 27

• histone 1 protein links nucleosomes to form a string of chromatosmes - 166bp

Question 28

what is the core histones functions

Answer 28

• H2A,H2B,H3 and H4
• wrap DNA
• form nucleosomes
• left handed superhelical ramp
• amino-terminal tail extension

Question 29

what are linker histones and what is their function

Answer 29

• H1 and H5
• higher order DNA structures
• bind nucleosomes at DNA entry and exit sites

Question 30

why to histones have variations

Answer 30

• specific functions
• insertion into nucleosomes at specific sites
• require ATP-dependent chromatin remodelling enzymes

Question 31

how are histones modified

Answer 31

• often N-terminal histone tails modified
• acetylation of lysines
• mono, di or tri methylation of lys/arg
• phosphorylation of serines
• lysine ubiquitylation
• mutually exclusive modifications

Question 32

what is ubiquitylation

Answer 32

• adds ubiquitin - 76 amino acid protein

Question 33

what are the reasons for histone modification

Answer 33

• recruit other structural proteins
• regulation of expression - loose/ tight structure
• cell memory - some modification kept

Question 34

where does topoisomerase 1 act

Answer 34

• tyrosine active site
• DNA nicked to allow rotation

Question 34

what does DNA topoisomerase do

Answer 34

• prevents DNA tangles

Question 35

what doe topoisomerase 2 do

Answer 35

• two circular DNA double helices that are interlocked
• cut to allow seperation
• allows strands to move over eachother

Question 36

what does topoisomerase 1 inhibitors do and what is the limitations

Answer 36

• mainly prevent colorectal and ovarian cancers
• examples - lamellarin D, irinotecan (CPT11), topotecan, and camptothecin
  limitations - inactivation in the blood, internal target - transporter expression required

Question 37

what are examples of topoisomerase 2 inhibitors

Answer 37

• etoposide and teniposide

Question 38

what do antibiotics do to topoisomerase inhibitors

Answer 38

• target topoisomerase 2 in bacteria
• examples - quinolones - milidixic acid and ciproflaxacin
• binds to cleavage-ligation active site leading to chromosomal breakages and excess DNA repair leading to cell death