Lecture 14

Question 1

What is meant by genetic heterogeneity?

Answer 1

-phenomenon where a single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus) mutations. -a phenotype can be the result of mutation in different genes e.g. deafness: 120 independent genes may result in deafness when mutated = genetically heterogenous trait

Question 2

What are the three processes in transcription?

Answer 2

-initiation-promoter recognition -elongation -termination

Question 3

What determines where RNA synthesis begins?

Answer 3

RNA polymerase binds to promoter regions and this determines where RNA synthesis begins -+1= start of transcription everything to the left= upstream, right= downstream promoters always upstream from the initiation point

Question 4

What is a promoter?

Answer 4

special DNA sequences recognised by the RNA polymerase 20-200 bases

Question 5

What is this?

Answer 5

-for RNA polymerase to bind we have to have the other proteins

Question 6

Describe:

Answer 6

enhancer- enhances transcription
yellow-influenced by protein binding or not binding
pink-where RNA polymerase binds
-DNA flips back, brings the enhancer in contact with the transcription complex and that will start tanscription

-what proteins in a cell at a time can switch genes on/off

Question 7

What does binding of a repressor protein do?

Answer 7

-blocks transcription

Question 8

What does binding of an activator protein do?

Answer 8

-stimulates transcription

Question 9

What happens at the transcription initiation?

Answer 9

RNA polymerase binds and DNA is denatured in this region
• DNA strands separate • First RNA nucleoside triphosphate is placed
at the site

-once RNA polymerase is bound- has to melt the DNA so it’s single stranded = opens up the strand

Question 10

What happens at transcription elongation?

Answer 10

• RNA polymerase moves along DNA template strand adding bases 5’ 3’ to growing RNA strand
  -bases are complementary to the DNA
  template

Question 11

What happens at transcription termination?

Answer 11

RNA polymerase reaches a chain termination sequence
This is a sequence which can form a loop
..CGTCCGA….TCGGACG.. ..GCAGGCA….AGCCTGC..
RNA polymerase and mRNA are released

RNA formed from the end sequence will bend on itself- then RNA poilymerase drops off

Question 12

What is reverse transcriptase?

Answer 12

some viruses have only RNA(instead of DNA as well), they employ enzyme reverse transcriptase to manufactire DNA out of RNA, this DNA can take over the machinery of the cell they’re infecting, take RNA make single-stranded DNA and make it double stranded by special PCR techique

Question 13

What is the difference in mRNA production in prokaryotes and eukaryotes?

Answer 13

• Prokaryotes the primary transcript is mRNA,so just have a single step since mRNA is the primary RNA in prokaryotes
• In eukaryotes the primary transcript is modified

and processed into mRNA,ot of processing before primary transcript is made into mRNa

Question 14

Where does the RNA processing take place?

Answer 14

-in the nucleus before it leaves to the cytoplasm

Question 15

What is the first step of RNA processing? (ends)

Answer 15

• The ends of the transcript are treated for stability and binding to the ribosome
• treated at its ends- modification there allows it to find its way through the nuclear membrane and to the ribosomes

modifications at both 3’ and 5’ end
5’- special methyl guanosine 7 Me G
3’- a whole sequence added of upto 200 adenines =capping(7 Me G) and tailing (adenine)

Question 16

What is hnRNA?

Answer 16

That is what we call the RNA primary transcript.

Question 17

What is the step no 2 in RNA processing? (splicing)

Answer 17

The mRNA is commonly spliced, the introns are removed and the exons (expressed sequences) joined up to make the final transcript

-there are sequences in the hnRNA that are cut out, the intervening sequences=introns= sequences that are transcribed but won’t go to be translated

-the sequences left behind are the expressed sequences= exons
hnRNA into mRNA by capping and tailing then splicing then mRNA

-alternative splicing of the same primary transcript may create different mRNA molecules

Question 18

Why do some genes have lot of introns? They require energy both to transcribe and splice out…

Answer 18

not clear…

some have so many! Distrophin 99% of it are introns!

Question 19

How do we name the strands in transcription?

Answer 19

Template strand is transcribed into a complementary mRNA sequence but the sequence on the mRNA is similar to the non template strand except U instead of A The non template strand is called the coding strand and is often used when showing a sequence because it represents the mRNA sequence

-the DNA strand with the sequenced being transcribed into RNA= template strand or non coding strand (opposite polarity to mRNA)
strand complementary to the template= coding strand because the sequence on coding strand is the same as the sequence on mRNA (except U instead of A) and the same polarity as the mRNA

Question 20

Can we get more protein types from one primary transcript?

Answer 20

-yes, the case of alternate splicing in trypomyosin

which of the introns are cut ot varies with tissue type example tropomyosin in skeletal muscle miss exon 2

• then get variance of the protein in different tissues
• more protein types from the same primary transcript

Question 21

How many times can a drophila gene be spliced?

Answer 21

Drosophila gene can be spliced in 36 096 ways

-from original transcript can get 36 096 ways!

Question 22

How is sex determination in drosphila connected to alternative splicing?

Answer 22

sxl gene produces tra protein as a consequence of that the sxl protein has an influence on the splicing of the RNA transcript
-in sex determination in drosphila- associated with differential splicing in the pathway

Question 23

How can alternative splicing account for the variance in the same genetic code?

Answer 23

Alternative splicing of the same primary transcript can lead to different polypeptides from the same DNA sequence

Question 24

How many essential amino acids are there?

Answer 24

20.

Question 25

How mamy bases per amino acid?

Answer 25

3

64 possible combinations

=degenerative= more than one combo for an amino acid

=the third base not as important

• for RNA= codons
• DNA= triplets

Question 26

What are codins tha code for the same amino acid called?

Answer 26

synonymous

Question 27

What are the 3 stop codons?

Answer 27

UAA UAG and UGA

Question 28

What is the start codon?

Answer 28

AUG

Question 29

What does it mean that genetic code is non-overlapping?

Answer 29

-the three bases are always read separately from beginning to the end

Question 30

Does every DNA sequence that is transcribed get translated?

Answer 30

No!

-mRNA is the only RNA to be translated into a polypeptide

ribosomal RNA for example, transfer RNA, micro RNA(doesn’t get translated)

Question 31

What does a gene include?

Answer 31

more than the sequence which codes for a polypeptide • eg., promoters, introns

Question 32

How many types of RNA polymerases are there in prokaryotes and eukarytoes?

Answer 32

NA polymerase transcribes the DNA only one type in prokaryotes several in
eukaryotes (RNA polymerase II transcribes DNA into RNA)

Question 33

How does the environment affect gene expression?

Answer 33

Gene expression is influenced by transcription factors (proteins) which determine
binding of RNA pol and may or may not be expressed in certain environments

It can also be enhanced or repressed by other factors that are distant from the
gene being expressed

Question 34

What is wobble in genetics?

Answer 34

-the last base of the triplet is not as important and more codons code for one amino acid