DNA to Proteins

Question 1

What does bp mean?

Answer 1

Base pairs

Question 2

What does kDa mean?

Answer 2

KiloDaltons, 1000 atomic mass units.
One Dalton is the mass of an H atom, or 1/12 of a C atom.

Question 3

What does S mean?

Answer 3

Svedberg unit, and refers to the mass and shape of cellular organelles.

Generally, high S means a larger mass.

S values are not additive e.g. bacterial ribosome (70S) consists of 50S and 30S subunits

Question 4

What is mRNA?

Answer 4

Messenger RNA (mRNA) is printed as a long linear transcript.

It then processed to the mature form (in proximity of the nuclear membrane).

It has a 5’CAP and a 3’ Poly A tail.

Question 5

What is tRNA?

Answer 5

tRNA carry amino acids to ribosomes, and check that they are incorporated in the right poistion.

Question 6

What does degenerate mean?

Answer 6

Many amino acids specified by more than one codon

But each codon specifies only one amino acid

Question 7

What factors initiate gene expression?

Answer 7

Proteins called “transcription factors” find their way into specific sequences 5’ of the 1st exon (region called “promoter”).

Question 8

What factors turn off gene expression?

Answer 8

Activation of repressors (inhibitors of RNA polymerase binding)

Question 9

What is splicing?

Answer 9

Removal of introns from mRNA

Question 10

What are introns?

Answer 10

Regions that do not code for proteins

Question 11

What are exons?

Answer 11

Regions that code for proteins

Question 12

What happens in transcription?

Answer 12

Transcription begins when the enzyme RNA polymerase binds to a region of a gene called the promoter sequence.

This signals the DNA to unwind so the enzyme can “read” the bases of DNA.

The two strands of DNA are named based on whether they will be used as a template for RNA or not.

The strand that is used as a template is called the template strand, or can also be called the antisense strand.

The sequence of bases on the opposite strand of DNA is called the non-coding or sense strand.

Once the DNA has opened, and RNA polymerase has attached, the RNA polymerase moves along the DNA, adding RNA nucleotides to the growing mRNA strand.

The template strand of DNA is used as to create mRNA through complementary base pairing.

Once the mRNA strand is complete, and it detaches from DNA.

The result is a strand of mRNA that is nearly identical to the coding strand DNA – the only difference being that DNA uses the base thymine, and the mRNA uses uracil in the place of thymine

Question 13

What are the 3 stages of translation?

Answer 13

Initiation
Elongation
Termination

Question 14

What happens in initiation?

Answer 14

After transcription in the nucleus, the mRNA exits through a nuclear pore and enters the cytoplasm.

At the region on the mRNA containing the methylated cap and the start codon, the small and large subunits of the ribosome bind to the mRNA.

These are then joined by a tRNA which contains the anticodons matching the start codon on the mRNA.

Question 15

What are mRNA, ribosomes and tRNA known as?

Answer 15

Initiation complex

Question 16

What happens in elongation?

Answer 16

tRNA keep bringing amino acids to the growing polypeptide according to complementary base pairing between the codons on the mRNA and the anticodons on the tRNA.

As a tRNA moves into the ribosome, its amino acid is transferred to the growing polypeptide.

Once this transfer is complete, the tRNA leaves the ribosome, the ribosome moves one codon length down the mRNA, and a new tRNA enters with its corresponding amino acid.

This process repeats and the polypeptide grows.

Question 17

What happens in termination?

Answer 17

At the end of the mRNA coding is a stop codon which will end the elongation stage.

The stop codon doesn’t call for a tRNA, but instead for a type of protein called a release factor, which will cause the entire complex (mRNA, ribosome, tRNA, and polypeptide) to break apart, releasing all of the components.

Question 18

What is protein synthesis?

Answer 18

Protein synthesis is the process in which cells make proteins. It occurs in two stages: transcription and translation.

Question 19

What are transcription factors?

Answer 19

Protein factors which control whether a gene is turned on or off