Transcription and translation

Question 1

What are genes made of?

Answer 1

DNA and are expressed in the phenotype as polypeptides

Question 2

What is the central dogma (principle) of molecular biology?

Answer 2

DNA—­­­­>RNA—>protein (transcription and translation)

Question 3

What do RNA viruses do to DNA?

Answer 3

They exclude DNA and directly transform RNA into protein.

Question 4

What do retroviruses do in transcription?

Answer 4

They reverse it

Question 5

What are the steps to express a gene?

Answer 5

1st DNA is _transcribed_ to RNA;
Then RNA is _translated_ into protein

Question 6

How is RNA transcribed?

Answer 6

1. It is transcribed from a DNA template after the bases of DNA are exposed by unwinding the double helix
2. RNA polymerase catalyzes (causes) transcription from the template strand of DNA
3. The initiation of transcription requires that RNA polymerase recognize and bind tightly to a promoter sequence on DNA
4. RNA elongates in a 5’ -to-3’ direction, antiparallel to the template DNA
5. Special sequences and proteins helpers terminate transcription

Question 7

What happens during elongation?

Answer 7

While the DNA unwinds and rewinds in the 5’ to 3’ direction RNA is doing transcription up until it reaches the termination site

Question 8

What composes the genetic code?

Answer 8

triplets of nucleotides (codons)
64 possible condons since there are 4 bases

Question 9

What are the codons’ roles?

Answer 9

• One mRNA codon indicates the starting point of translation and codes for methionine (amino acids)
• 3 stop codons indicate the end of translation
• the other 60 condons code only for particular amino acids

Question 10

Why is the genetic code called redundant?

Answer 10

Since there are only 20 different amino acids, there is more than one codon for certain amino acids

But a codon can only be found in a specific amino acid, meaning it is unambiguous (always codes for the same amino acid)

Question 11

What is the start codon?

Answer 11

AUG (Methionine)

Question 12

What are the 3 stop codons?

Answer 12

UAA, UAG, UGA

Question 13

When does translation start for prokaryotes?

Answer 13

Before mRNA is completed

Question 14

Where do transcription and translation happen in eukaryotes?

Answer 14

Transcription happens in the nucleus and translation happens in the cytoplasm

Question 15

What components does translation need?

Answer 15

tRNA’s, activating enzymes and ribosomes

Question 16

What does tRNA?

Answer 16

It carries amino avcids to the protein synthesizing machinery of a cell called ribosome

Question 17

Who do the aminoacyl-tRNA synthetases do?

Answer 17

Attach specific amino acids to their appropriate tRNAs, forming charged tRNAs

Question 18

What are the large subunits of the ribosome?

Answer 18

E, P,A and T

Question 19

What triggers translation?

Answer 19

An amino acid-charged tRNA and a small ribosomal subunit bound to mRNA

Question 20

How do polypeptides grow ?

Answer 20

From 5’ to 3’ of mRNA

Question 21

On what and how does a ribosome move?

Answer 21

It moves along the mRNA one codon at a time

Question 22

How does translation stop?

Answer 22

The presence of a stop codon in the A site of the ribosomes causes the termination

Question 23

What is an anticodon?

Answer 23

They are the complementary nucleotides of the start codon (on mRNA), which are isolated on tRNA

Question 24

Explain the process

Answer 24

1. The ribosome moves along the mRNa one codon (three nucleotides) at a time. until it comes upon the start codon (AUG)
2. Then the tRNA with the anticodon of the start codon comes in the P subunit with an amino group (amino terminus) at its C end terminus (3’)
3. Another tRNA comes in the A site with another amino group. The ribosome continues moving and the first tRNA leaves leaving its amino group on the amino group of the new tRNA
4. This process continues until the ribosome comes over the stop codon
5. Then a release factor comes in the A unit over the stop codon and then the tRNA goes away and leaves the polypeptide floating.
6. The C-terminus and N-terminus come at each end of the chain of amino groups to form a polypeptide