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. DNA RNA RNA contains the pentose sugar ribose.
DNA contains the pentose sugar deoxyribose.
DNA
RNA

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