Lecture 19: Genetic Code II

Question 1

Does it matter which strand of DNA, RNA polymerase transcribes?

Answer 1

Yes, it does because they are antiparallel, RNA polymerase must know which strand to transcribe

Question 2

Sense strand

Answer 2

Strand that is not transcribed but has the same sequence as the mRNA

Question 3

Template Strand

Answer 3

Strand that is transcribed and has a complementary sequence to mRNA

Question 4

What are promoters?

Answer 4

Special sequences on DNA that the RNA polymerase recognize as the start of a gene

Question 5

Is the promoter sequence transcribed?

Answer 5

No

Question 6

Which strand is the template strand?

Answer 6

The strand that is in the 5’ to 3’ direction

Question 7

TATA Box

Answer 7

promoters bind to it

Question 8

Reading Frames

Answer 8

Different ways to read a genetic sequence

Question 9

True or False: ribosome picks the right reading frame ?

Answer 9

True

Question 10

How does the ribosome know where to start?

Answer 10

-The right reading frame always starts with the start codon AUG
-The small subunit finds AUG in the mRNA and binds to it along with the tRNA for methionine

Question 11

What is the ribosome made of?

Answer 11

Two large subunit of rRNA and proteins

Question 12

What happens when the large ribosomal sub unit binds?

Answer 12

-The large ribosomal sub unit has two tRNA binding sites, A-site and P-site
-Large subunit binds so tRNA met is in the P-site, the the next tRNA that corresponds to the codon will bind to the A-site

Question 13

How are peptide bonds between amino acids formed?

Answer 13

• 3’ hydroxyl of amino acid in P-site creates a peptide bond with amino acid in A-site

Question 14

What happens to the tRNA after the peptide bond is formed?

Answer 14

-tRNA in the A-site is released and then the ribosome shifts a distance of one codon in the 3’ direction

Question 15

What happens once the ribosome reaches a stop codon?

Answer 15

-A release factor protein binds to the A-Site, causing the last tRNA to release the polypeptide chain and the ribosome to disassemble

Question 16

Wobble pairing

Answer 16

-The tRNAs can bind to more than one codon

Question 17

Polysome?

Answer 17

Multiple ribosomes translating the same piece of mRNA

Question 18

Is the central dogma process sequential ?

Answer 18

No, ribosomes can be translating mRNA before transcription is finished

Question 19

Missense mutation?

Answer 19

Change in one single amino acid in a protein(SICKLE CELL)

Question 20

Two broad categories for mutations?

Answer 20

1. Point mutations: small changes in the DNA usually only affecting one gene
2. Chromosomal Mutations: changes that affect a large portion of a chromosome, often affecting many
   genes

Question 21

True or False: If a change occurs in the sense strand the nonsense strand will also be changed?

Answer 21

True

Question 22

Silent mutations

Answer 22

Do not affect the proteins because of the degeneracy of the code(point)

Question 23

Missense mutations

Answer 23

Changes one amino acid to another(point)

Question 24

Nonsense mutations

Answer 24

Change an amino acid to a stop codon(shortens protein)(point)

Question 25

Frame shift

Answer 25

insertion/deletion of amino acid (if insertion/deletion happens in three it does not cause a frame shift but does add/delete an entire amino acid)(point)

Question 26

Deletions

Answer 26

removing a large piece of chromosome including many genes(CM)

Question 27

Duplications

Answer 27

Duplicate large chunks of the chromosome(CM)

Question 28

Inversion

Answer 28

Piece of DNA is flipped around, re-entering the chromosome in reverse order(CM)

Question 29

Translocations

Answer 29

Piece of DNA jumps from one chromosome to another
Reciprocal translocations: two chromosomes trade pieces of DNA(CM)

Question 30

Mutagens

Answer 30

-Agents that cause changes in the DNA sequence
Ex. Chemicals, Radiation, Viruses

Question 31

What happens if the mutation is in the somatic cell?

Answer 31

-The change could kill the cell, cause cancer, make the cell sick
-Every cell that derives from that cell will be affected by the mutation
-The change will not be transmitted to the progeny

Question 32

What happens if the mutation is in the gamete?

Answer 32

There is a possibility that an egg/sperm will end up with the mutated gene and transmit it to the progeny
- It is on these germ lines that natural selection acts
-Can become a new alley in the population if it is not harmful/beneficial