Chapter 6 CMB RNA & Protein Synthesis

Question 1

What are chromosomes made up of?

Answer 1

DNA + histone proteins
Segments of DNA code for a protein
Protein in turn, relates to a trait (eye colour, enzymes, hormones..)

Question 2

How are proteins synthesized from DNA?

Answer 2

1. DNA is transcribed into mRNA (messenger RNA)
2. mRNA leaves the nucleus and travels to the cytoplasm
3. The mRNA sequence is then translated into amino acids in the ribosomes
4. Amino acids form a peptide chain - a protein

Question 3

What is the Central dogma?

Answer 3

DNA (replication) > RNA (transcription) > Proteins (translation)

Question 4

State the 3 types of RNA

Answer 4

1. Messenger RNA (mRNA)
2. Ribosomal RNA (rRNA)
3. Transfer RNA (tRNA)

Question 5

Role of messenger RNA (mRNA)

Answer 5

Bring information and acts as a template for a new protein to produce.

Question 6

Role of ribosomal RNA (rRNA)

Answer 6

Site where protein synthesis occurs

Question 7

Role of transfer RNA (tRNA)

Answer 7

Bring amino acids to the ribosomal subunits, where protein synthesis takes place

Question 8

What is the process of making mRNA called?

Answer 8

Transcription

Question 9

What are the main ingredients needed for mRNA synthesis? 5

Answer 9

1. DNA template (one of the strands of DNA)
2. RNA polymerase – to synthesize mRNA
3. rNTP’s - bases for the mRNA (A,U,C,G)
4. Transcription factors – required to carry the RNA polymerase and complete the mRNA synthesis
5. ATP – required to begin the mRNA synthesis

Question 10

What happens during transcription of DNA

Answer 10

A strand of RNA complementary to the DNA is formed; the mRNA

Question 11

State the 4 steps of transcription

Answer 11

1. Enzyme RNA polymerase binds tightly to a promoter.
2. RNA polymerase opens up the DNA helix.
3. The enzyme adds new RNA nucleotides that are complementary to the template DNA.
4. mRNA is made.

Question 12

What are the 3 processing steps of newly synthesized primary mRNA?

Answer 12

1. Capping
2. Addition of poly A tail
3. Splicing

Question 13

Why is processing needed?

Answer 13

Processing is necessary as it stabilizes the mRNA.
Only mRNAs with cap and tail remain active in the cell.

Question 14

What happens after processing?

Answer 14

-After processing, it is now known as the mature mRNA
-Leave the nucleus into the cytoplasm where it gets associated with the ribosomes.

Question 15

What is splicing?

Answer 15

• Excision and rejoining process of RNA.
• The removal of introns.

Question 16

What are exons?

Answer 16

Exons are called coding sequences and code for proteins

Question 17

What are introns and why are they removed during processing?

Answer 17

Introns are called non-coding sequences and do not code for proteins. Hence, they have to be removed.

Question 18

What are the main ingredients for translation? 7

Answer 18

1. mRNA
2. Transfer RNA (tRNA)
3. Ribosomes
4. Amino acids
5. Start codon (AUG)
6. Stop codon (UAG/UAA/UGA)
7. Release factors (scissors)

Question 19

What is start codon & stop codon?

Answer 19

Start codon (AUG) – place where translation begins
Stop codon (UAG/UAA/UGA) – place where translation ends

Question 20

What are release factors?

Answer 20

When ribosome approaches the stop codon these factors come and contact with the A site of the ribosomes and stop the process.

Question 21

What happens during translation? 3 steps.

Answer 21

1. Initiation
2. Elongation
3. Termination

Question 22

What happens during initiation in translation?

Answer 22

1. Small ribosomal subunit attaches to the mRNA close to the start codon (AUG).
2. Anticodon of the initiator tRNA-methionine complex pairs with this codon.
3. Large ribosomal subunit joins to the small subunit

Question 23

What happens during elongation?

Answer 23

Two tRNAs can be at a ribosome at one time. The tRNA at the P site passes its peptides to the tRNA at the A site. The tRNA at the P sites leaves. The ribosome move forward (translocation), and the tRNA-peptide complex is now at the P site. A new tRNA-amino acid complex comes to the A site.

Question 24

What happens during termination?

Answer 24

When stop codon (UAA, UAG & UGA) appears at the A site of a ribosome, termination occurs.

A protein called release factor binds to the stop codon and cleaves the polypeptide from the last tRNA.

Question 25

What is the release factor protein for during termination?

Answer 25

binds to the stop codon and cleaves the polypeptide from the last tRNA.

Question 26

What is the combination for Synthetic RNA triplet & charged tRNAphe?

Answer 26

Synthetic RNA triplet - UUU
Charged tRNAphe - AAA

Question 27

What are properties of tRNA? 4

Answer 27

1. Transfers amino acids to the ribosome during translation
2. tRNA acceptor stem carries amino acid
3. The tRNA anticodon can form hydrogen bonds with its complementary mRNA codon.
4. Two side loops are recognized by enzymes which add the correct amino acid to the tRNA

Question 28

What is a 1 triplet codon?

Answer 28

A start codon (AUG), which codes for the amino acid methionine (MET)

Question 29

What are 3 triplet codons?

Answer 29

3 triplet codons are stop codons (UAA, UAG, UGA), which do not code for any amino acid and specify polypeptide chain termination