Unit 2 - 8. Gene Expression: Transcription and Translation

Question 1

Gene expression

Answer 1

• DNA does this by coding for proteins in the body using RNA as intermediate

Question 2

Central Dogma

Answer 2

DNA -(Transcription)-> RNA -(Translation)-> Protein

Question 3

Transcription

Answer 3

• DNA converted to complementary base sequence of mRNA in nucleus

Question 4

Translation

Answer 4

mRNA converted to linear sequence of amino acid = protein

Question 5

Promoter sequence

Answer 5

• a specific sequence of nucleotides in the 5’ flanking region of DNA that RNA polymerase binds to

Question 6

Sense Strand

Answer 6

• “coding strand”, complementary to the antisense strand and is the same sequence of the mRNA that will undergo translation

Question 7

Antisense strand

Answer 7

• aka missense strand

- read 3’-5’ in transcription to make mRNA

Question 8

Exon

Answer 8

• sequences that are expressed (code for protein)

Question 9

Intron

Answer 9

• non-coding (intervening) sequences

- 90% of gene are introns

Question 10

Splicing

Answer 10

• removal of introns and joining together of exons

Question 11

codon

Answer 11

• set of 3 nucleotide that code for one amino acid

Question 12

anticodon

Answer 12

• 3 nucleotides in tRNA complementary to codon sequence on mRNA

Question 13

Transcription

Answer 13

• Initiation = RNA polymerase binds to promoter sequence (requires transcription factors) and the DNA helix unwinds.
• Elongation = RNA polymerase reads the anti-sense strand (3’-5’) and adds nucleotides (ATP, GTP, CTP, UTP) to 3’ end (builds 5’ - 3’)
• Termination = elongation stops when termination sequence in DNA is reached. mRNA and RNA polymerase release, DNA returns to its normal structure

Question 14

mRNA processing

Answer 14

• pre-mRNA includes exons and introns, splicing must take place to remove this
  + further modification:
  1. addition of guanosine cap (5’)
  2. poly- A tail (3’)
• creates stable mRNA to be transported from Nucleus to cytoplasm

Question 15

Reverse transcriptase

Answer 15

RNA (retrovirus) -(reverse transcriptase enzyme)-> cDNA -(RNA polymerase)-> mRNA

Question 16

Properties of Codons

Answer 16

1. Codons are degenerate (more than one codon can code for an Amino acid)
2. Amino acids with similar chemical properties have related codons
3. The code is nearly universal (all organisms use same codons)

Question 17

Translation

Answer 17

Initiation: (forms initiation complex)

• mRNA binds to small subunit of ribosome
• tRNA carrying start codon binds to mRNA
• large ribosomal subunit binds

Elongation:
- other tRNAs with matching next anticodon adds one at a time as ribosome shifts down and peptide binds form between amino acids

Termination:

• elongation stops when stop codon is reached (because there is no tRNA with an anticodon complementary to stop codon)
• peptide is released from ribosome

Question 18

Regulation of Gene Expression: DNA Level

Answer 18

DNA methylation to cytosine bases - condenses chromatin and prevents binding of transcription factors

Question 19

Regulation of Gene Expression: Transcription Level

Answer 19

• Chromatin remodeling (of histones to make promoters accessible or not )
• alternate splicing
• post transcriptional regulation via siRNA = RNA interference cleaves mRNA

Question 20

Regulation of Gene Expression: Translation Level

Answer 20

• length of poly A tail (longer = increased production rate)
• post-transational modifications = folding, adding lipids/carbs, modify/removing amino acids
• control of protein break down