Nucleic Acids and Gene Expression

Question 1

What are the building blocks of nucleic acids?

Answer 1

• sugar
  
  • 5 carbon pentose sugar
  • ribose in RNA and deoxyribose sugar in DNA
• bases
  
  • purines: adenine and guanine
  • pyrimidines: thyamine and cytosine
• phosphoryl group
  
  • oxygen of phosphate binds to carbon 5 of sugar

Question 2

What does DNA stand for?

Answer 2

Deoxyribonucleic Acid

Question 3

What does RNA stand for?

Answer 3

Ribonucleic Acid

Question 4

What are DNA/RNA?

Answer 4

biopolymers of nucleotides

Question 5

What is DNA/RNA primary structures?

Answer 5

• nucleotides are joined by phosphodiester bonds between adjacent carbons of deoxyribose sugars
• only variable groups in this sequence are the bases so describing primary structure of DNA requires reporting the base sequence
• DNA and RNA are slightly acidic due to deprotonation of the hydroxyl group at physiological pH
• DNA has a distinct secondary structure (double helix) whereas RNA exists in a single stranded structure
• the structure of DNA is key in controlling the flow of genetic information

Question 6

How does DNA replication work?

Answer 6

• separation of strands
  
  • helicase breaks hydrogen bonds to unzip DNA molecule
• primer bonding
  
  • a small strip of RNA (primer) ‘kick start’ replication
• elongation
  
  • DNA polymerase adds complementary base pairs in the 5’ to 3’ direction
  • this builds a new DNA molecule that wraps around the parental strand
• termination
  
  • exonuclease removes the original primers and the bases are then readded to complete a new DNA double helix

Question 7

How does mutation of DNA occur?

Answer 7

• bases can be inserted or deleted incorrectly resulting in a change in the protein formed
• an advantageous mutation forms the basis of darwins theory of evolution

Question 8

What are the different types of RNA?

Answer 8

• messenger (mRNA)
  
  • decodes DNA
• ribosomal (rRNA)
  
  • decodes mRNA
• transfer (tRNA)
  
  • facilitates protein formation

Question 9

What is transcription?

Answer 9

• DNA unwinds and RNA polymerase replicates DNA template to form mRNA primary transcipt
  
  • promotors: DNA region next to transcription site that docks RNA polymerase
  • enhancers: DNA regions that attract the transcription factor complex proteins
  • transcription factor complex: proteins that regulate the take of mRNA formation

Question 10

How does exercise regulate gene expression?

Answer 10

• the amount and/or types of cell signals will modulate the number of mRNA copies made by:
  
  • regulating promoter and enhancer activity
  • altering transcription factor activity
  • controlling access of RNA polymerase to the gene
• gene expression is governed by signals sent to the cell after exercise
• the signals produced from different types of exercise will result in a different region of the gene being copied and different mRNA and proteins being produced

Question 11

What is mRNA splicing?

Answer 11

• primary mRNA transcript is not the final mature mRNA that then codes for protein translation
• processing in the nucleus splices introns - excised, non coding regions of mRNA
• remaining exons form mature mRNA and exons
• alternate mRNA splicing can accounts for different isoforms of proteins i.e. tropmyosin

Question 12

What is translation?

Answer 12

• the formation of a polypeptide chain from a mature mRNA transcript
• mRNA binds to the small subunit of ribosomal RNA where it is decoded and a signal sent by ribosomal proteins to the large subunit where translation then begins
• a 3 base sequence on a mRNA transcript complements a 3 base sequence on a transfer RNA molecule which binds to the large subunit of rRNA holding an amino acid
• this interaction facilitates the formation of a new polypeptide chain via peptide linkages