products of transcription

mRNA

copy of DNA which codes for the protein

tRNA

small adaptor molecules which align specific amino acids opposite their triplet codon in the mRNA molecule

rRNA

• makes up ribosomes

• important for protein synthesis

the ‘cap’ in RNA capping is also called:

7-methylguanosine

poly-A tail is made up of

long string of adenosines attached to 3’ end of mRNA

roles of 5’ end cap and 3’ end polyadenylation

• assists the export of mRNA molecules from the nucleus

• protect the mRNA from degradation in the cytoplasm and increase its half life

• enables the binding of ribosomes and promotes translation

degeneracy within the amino acid code

• some amino acids can be coded for more than one codon

• e.g. leucine can be encoded by 6 codons

• e.g. methionine is encoded by 1 codon

bases other than the main 4 in DNA are present in tRNA as a result of ?

post-transcriptional modification

inosine is the modified version of

adenine

the ? of tRNA determines attachment of particular amino acid

shape

the amino acid attachment site is at ? end of tRNA

3’ end

amino acids are attached to their corresponding tRNA via what enzyme?

aminoacyl-tRNA synthetases

D and T loop

recognised by the aminoacyl tRNA synthetases

anticodon loop

• contains the anticodon which is recognised by the aminoacyl-tRNA-synthetase

• codes for corresponding amino acid attached to 3’ end of tRNA

aminoacyl-tRNA synthetases are specific to a particular (?)

amino acid

when the correct amino acid has been attached to its tRNA, the tRNA is said to be:

charged (or acylated)

a charged tRNA is termed:

amino acyl tRNA

prokaryotic ribosome structure

• 5S, 23S rRNA in their large ribosomal subunit

• 16S rRNA in their small ribosomal subunit

eukaryotic ribosome structure

• 5S, 5.8S and 28S rRNA in their large ribosomal subunit

• 18S rRNA in their small ribosomal subunit

small subunit vs large subunit function (ribosomes)

• small subunit reads codon and matches corresponding tRNA

• large subunit contains three sites and is primarily responsible for the formation of peptide bonds that link the amino acids together into a polypeptide

each ribosome has (a) binding site for mRNA and (b) binding sites for tRNA

(a) 1

(b) 3

A site

new tRNA enters ribosomal complex

P site

where tRNA amino acid attaches to polypeptide chain

E site

empty tRNA exits after amino acid detaches

explain the diagram

1. Amino acyl tRNA (4) binds to A-site

• Anticodon base pairs with codon in mRNA

• Simultaneously tRNA (2) leaves from E-site

2. Formation of peptide bond between amino acid 3 and 4

3. Large ribosomal subunit moves to the right along mRNA

4. Small ribosomal subunit moves to the right along mRNA

• tRNA (4) is now in P-site

• tRNA (3) is now in E-site

5. Amino acyl tRNA (5) bind to A-site

• Anticodon base pairs with codon in mRNA

• Simultaneously tRNA (3) leaves from E-site

eukaryotic ribosomes recognise a ? to initiate translation

5’ cap

prokaryotic ribosomes initiate translation at (?) sites

ribosome-binding sites

as ribosome-binding sites are located throughout an mRNA molecule, this allows prokaryotes to:

prokaryotes can synthesise more than one type of protein from a single polycistronic mRNA molecule

polyribosome

large assembly of several ribosomes on a single mRNA molecule