The Structure Of Biomaterials: DNA

Question 1

DNA function

Answer 1

• controls all chemical changes which take place in the cell
• DNA determines what kind of cell is formed via gene expression

Question 2

DNA structure

Answer 2

• DNA made up of long chain of sub-units: nucleotides
• Each nucleotide made up of a sugar called deoxyribose, a phosphate group and an organic base
• Double helix structure stabilised by hydrogen bonding with negatively charged PO4 backbone on the outside
• also stabilised by pi-pi stacking

Question 3

DNA replication

Answer 3

Basic principle: Base pairing to template strand
- each strand of DNA acts as template for building a new strand
- parent molecule unwinds and two new daughter strands are built
- Each 2-stranded daughter molecule is only half new as one original strand was used as template to make new strand

Question 4

Origin of replication

Answer 4

• The replication of DNA begins at special sites called origins of replication where two parental strands separate and form replication bubbles
• Replication bubbles expand laterally and fuse, synthesis of daughter strands is then complete

Question 5

Mechanism of DNA replication

Answer 5

• DNA replication catalysed by DNA polymerase which needs an RNA primer
• RNA primase synthesises primer of DNA strand
• DNA polymerase adds nucleotides to the 3’ end of growing strand

Question 6

Protein Synthesis: Transcription and Translation

Answer 6

• inherited DNA dictates synthesis of proteins, leading to traits
• cellular chain of command: DNA > RNA > Protein
• Transcription: the synthesis of RNA under direction DNA, it produces mRNA
• Translation: the synthesis of a polypeptide which occurs under direction of mRNA - occurs on ribosomes

Question 7

Transcription

Answer 7

• RNA synthesis is catalysed by RNA polymerase which separates DNA strands and hooks together RNA nucleotides
• follows same base pairing rules and DNA

Question 8

RNA structure

Answer 8

• single stranded
• only 1 gene long
• uses sugar Ribose instead of deoxyribose (DNA)
• uses base uracil instead of thymine (DNA)

Question 9

Translation

Answer 9

• Translation is the RNA directed synthesis of a polypeptide
• involves mRNA, ribosomes, transfer RNA, genetic coding

Question 10

The genetic code

Answer 10

• Codons: 3 Base code for production of amino acid, sequence of three or four different nucleotides
• 4 bases and 3 positions for each codon - 64 possible codons
• 3 of 64 used as stop signals found at end of every gene
• 1 codon used as start signal found at the start of every protein
• A codon in messenger RNA is translated into an amino acid or serves as start stop signal

Question 11

Transfer RNA

Answer 11

• consists of single RNA strand about 80 nucleotides long
• each carries amino acid on one end and anticodon on the other
• anticodon: 3 RNA bases that matches 3 bases of codon on mRNA molecule
• enzymes pair up tRNA molecules with corresponding amino acids
• tRNA brings amino acids to ribosomes

Question 12

Ribosomes

Answer 12

• facilitate coupling of tRNA anticodons with mRNA codons during protein synthesis
• 2 ribosomal subunits are constructed of proteins and RNA molecules