Gene expression

Question 1

Gene expression?

Answer 1

DNA directs its synthesis to proteins and RNA

Question 2

The order?

Answer 2

DNA –> premRNA–> mRNA –> polypeptide

Question 3

4^3?

Answer 3

64 different code words based on a code of tripletts.

Question 4

The mRNA molecule?

Answer 4

Complementary and is synthesized in antiparalell direction to the template strand.

3’ - ACC -5’
5’- UGG- 3’

Coding strand is the non-template strand

Question 5

Distribution?

Answer 5

61 of 64 codes for AA

1 start codon - AUG
3 stopp codon - UAA UGA UAG

Question 6

Reading frame?

Answer 6

Read in 5’–>3’ and the cells machinery reads them as a series of nonoverlapping three-letter words

Question 7

Transcription?

Answer 7

RNA Pol separate the strands and attaches to the promoter region TATA-BOX and adds to the growing 3’ end in 5’–>3’ direction. It moves along the strand and exposes 10-20 DNA molecules that pair up with RNA molecules until it reaches a polyadenylation signal in the DNA - polyadenylation signal - AAUAAA in the premRNA.

Question 8

I E T?

Answer 8

Initiation elongation and termination

Question 9

RNA processing?

Answer 9

G-CAP @ 5’ end and Poly-A-Tail @ 3’ end that protects, helps in transport and ribosomal attachment

Question 10

RNA splicing?

Answer 10

Introns are removed by splicesome and exons are put together

Question 11

Alternative splicing?

Answer 11

Genes gives rise to 2 or more different PP depending on which segments are treated as exons. Results in a higher amount of protein products that can be much higher then the number of genes.

Question 12

Exon-shuffling?

Answer 12

Introns increase the probability of crossover between exons of alleles of a gene providing new combos of exons —> structure and function.

Question 13

Translation?

Answer 13

tRNA with anticodon - 3’–>5’ that binds to the codon on the mRNA strand in 5’–>3’ direction by aminoacyl tRNA syntheases.

Question 14

Wobble?

Answer 14

The 3rd base @ a codon and anticodon is relaxed and provides a flexible base pairing.

Question 15

Binding sites?

Answer 15

P-site - peptidyl tRNA that holds the growing chain
A-site - aminoacyl tRNA that holds the tRNA carrying the next aa.
E-site - exit

When PP is completed it leaves through the exit tunnel in the large subunit.

Question 16

Translation initiation complex?

Answer 16

Startcodon on the mRNA and the small subunit binds to both the mRNA and the tRNA and scans downstream until it reaches the startcodon and then the large subunit binds. Done by initiation factors and hydrolysis of GTP.

Question 17

Release?

Answer 17

Moves in 5’–>3’ direction relative to the ribosome and stops when stopcodon reaches the A-site and a release factor and hydration reaction of H2O instead of AA to the PP. This breaks the bond between them.

Question 18

Post translational modification?

Answer 18

Primary - seondary - tertiary - quarternary and the addition of cho lipids or phosphate.

Ribosomes on ER gets a PP marked by a signal peptide recognized by SRP and the PP moves into ER lumen via a pore and is embedded in the membrane or travels to its destination in a vesicle.

Question 19

Mutations?

Answer 19

Provides diversity and ultimate source of new genes

Question 20

Small scale?

Answer 20

Substitutions - deletions - insertions

Question 21

Substitutions?

Answer 21

Silent - Change in the 3rd base of a codon that translates the same AA
Missense - Change in 2nd base to an AA with similar properties or may not have essential to the proteins functions
Nonsense - Change of AA to a stopcodon that results in a shorter PP that gives a non-funtional protein

Question 22

Addition or deletions?

Answer 22

Results in alteration of the reading frame of the codon on the mRNA during translation

Frameshift mutation - if not a multipple of 3 will affect all the nucleotides downstream since it will be improperly grouped into codons.

Usually results in missense and non-sense unless the frameshift is near the end of that gene.

Question 23

New mutations?

Answer 23

Errors during DNA replication or recombination.

Question 24

A gen?

Answer 24

A region of DNA that can be expressed to produce a final functional product that is either a PP or an mRNA molecule.