Ribonucleic Acid

1
Ribonucleic Acid

• RNA

2
The structure of ribonucleic acid

• Learning Objectives
• Describe the structure of ribonucleic acid (RNA)
• Describe the structure and role of messenger RNA
  (mRNA)
• Describe the structure and role of transfer RNA
  (tRNA)
• Describe the structure and role of ribosomal RNA
  (rRNA)

3
RNA

• RNA ribonucleic acid
• RNA is a single -stranded polymer
• Each RNA nucleotide consists of
• A pentose sugar (ribose)
• A phosphate group
• A base adenine, cytosine, guanine, uracil
  (instead of thymine)
• RNA used in protein synthesis is messenger RNA
  (mRNA) or transfer RNA (tRNA).

4
RNA contains the pentose sugar ribose. DNA
contains the pentose sugar deoxyribose.
RNA
DNA
5
The Genetic Code (recap)

• 3 nucleotide bases on mRNA (a codon) codes for
  each amino acid in a protein (DNA triplet
  code).
• A few amino acids have a single codon.
• The code is degenerate most amino acids have
  more than one codon.
• 3 codons code for no amino acids they are stop
  codons and mark the end of the polypeptide chain.
• Non-overlapping each nucleotide is read only
  once.
• Universal same codon codes for the same amino
  acid in all organisms (few minor exceptions).

6
mRNA (m messenger)
7

• tRNA (t transfer)

Amino acid joins here
Anticodon
8

• Complete the worksheet
• DNA RNA Comparison

9
Messenger RNA (mRNA)

• Used to transfer the DNA code from the nucleus to
  the cytoplasm, 1 gene at a time.
• Complementary to the DNA code.
• Small enough to leave the nuclear pores.
• Once in the cytoplasm, mRNA associates with the
  ribosomes.
• Easily broken down and only exists whilst it is
  needed to manufacture a protein.

10
Transfer RNA (tRNA)

• Small molecule (80 nucleotides).
• Single stranded and folded into a clover leaf
  shape with one end of the chain slightly longer.
• This longer section is attached to an amino acid.
• Each tRNA carries a different amino acid.
• 3 bases at the opposite end of the tRNA are
  called an anticodon.
• Each amino acid has a different anticodon.
• The anticodon pairs with the complementary codon
  on the mRNA.

11
Ribosomal RNA (rRNA)

• Ribosomes are small organelles, consisting of
  two subunits
• The large subunit consists of 2 strands of rRNA
  and 34 protein molecules
• The small subunit consists of 1 strand of
  rRNAand 21 protein molecules
• The ribosome is roughly equal parts RNA and
  protein in terms of mass
• Eukaryotic ribosomes are slightly larger than
  prokaryotic ribosomes (80S compared to 70S)
• The ribosome is the site of protein synthesis