L. 4 The Central Dogma of Molecular Biology

Question 1

L.O.

Answer 1

1. Outline the central dogma of molecular biology and describe the
   information flow between DNA, RNA and Proteins
2. Define the genome, transcriptome and proteome and how they differ from
   cell to cell.
3. Appreciate the difference in size and construction between bacterial and
   eukaryotic genomes
4. Define the universal genetic code (triplet/non-overlapping/common)
5. Understand the concept of reading frames for translating a nucleic acid
   sequence into a protein sequence
6. Understand how to read a genetic code table and translate nucleic acid
   sequence into protein sequence using such a table.
   Learning Outcomes

Question 2

The key components

Answer 2

Genome
- All of the DNA
- Complete set of Genetic info

Transcriptome
- All of the RNA produced by a cell at one time

Proteome
- All of the proteins

Question 3

DNA is…

Answer 3

Double stranded
- Provides 2 copies and a template for repair. Obvious mechanisms for replication/ transcription via base pairing

Stable
- Not prone to degradation: cells can reapairncytosine deamination (converting cytosin to uracile spontaneously)

Question 4

Bacterial Genomes

Answer 4

• Most prokaryotes have circular chromosomes
• Tend to be very small

Question 5

Eukaryotic genomes

Answer 5

• Tend to have big genomes
• Linear chromosomes condensed into chromatin, and wrapped in histone proteins

Question 6

The transcriptome

Answer 6

RNA in a cell or tissue at any given time
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)

Question 7

RNA as the messenger, the different roles

Answer 7

• mRNA is the messenger for making proteins
• microRNA and SnRNA have regulatory roles
• rRNA and tRNA are important for protein synthesis

Question 8

mRNA

Answer 8

• Messenger that encodes proteins (what the protein will be)
• Often many copies of mRNA are made to synthesise lots of protein at once
• Once mRNA has been used, it is degraded nia ribose
• Cytosine deamination in mRNA is not a problem as it will be degraded soon anyway, same reason mRNA is less stable than DNA

Question 9

The Proteome

Answer 9

• All the proteins expressed in a cell/ tissue at a given time
• Proteins are folded to have a specific function

Question 10

Proteins

Answer 10

The amino acids sequence determines the structure which determines the function

Question 11

The Genetic code

Answer 11

DNA undergoes transcription into RNA
RNA is translated into proteins

Question 12

Possible codes

Answer 12

Singlet
- 4 different bases and usually one position to have 4 different combinations (A,G,C,T/U)
Doublet
- 16 different possible pairs

Triplet
- 64 possible sets of 3

The order of the codes is very important AU≠UA

Question 13

Non-overlapping triplet code

Answer 13

Codons:
- Sets of 3 bases

Used to decifer amino acid chains

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Question 14

Reading Frames

Answer 14

While refering to the genetic code table
Read code from left to right (5’ to 3’).
AUG is the start codon

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Question 15

Mutations on DNA

Answer 15

• can be a massive problem when a protein is not made
• A mutation on DNA can lead to a protein not being made in the body

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