Higher Level

You need:
1. A supply of amino acids – cytoplasm
2. Instructions as how to join the amino acids together – genetic code
3. An assembly line – ribosomes
4. A messenger to carry information from
DNA to ribosomes

1. Transcription
2. Translation
• Remember: DNA

RNA

Protein

1. Ribose: smaller sugar than deoxyribose of
DNA
2. Phosphate
3. 4 Nitrogenous Bases A,G,U,C
RNA is single stranded and thus smaller & able to leave the nucleus of the cell

Transcription Translation
DNA


Nuclear membrane
DNA
Transcription
Eukaryotic
Cell
RNA Processing mRNA
Ribosome
Translation
Protein

DNA


DNA
Transcription mRNA
Ribosome
Translation
Protein
Prokaryotic Cell – No nucleus

• What is RNA composed of?
• How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid) ?
• What are the three stages in Protein synthesis?

Eukaryotic
Cell
Pic BBC bitesize

• The transfer of information in the nucleus from a DNA molecule to an RNA molecule.
• Only 1 DNA strand serves as the template
• When complete, mRNA molecule is released into the cytoplasm

• Takes places in the nucleus of the cell
The process by which the information from DNA is transferred to RNA.
DNA uncoils and unzips.
• The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

DNA
RNA Polymerase mRNA
Enzyme

This is a molecule of messenger RNA.
It was made in the nucleus by transcription from a DNA molecule.
codon
A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

• What type of RNA molecule is responsible for taking the DNA copy from the nucleus into the cytoplasm
• What parts of the cell do you find RNA in?
• Can you outline the stages in transcription?

• Takes place in the nucleus of the cell
The process by which the information from DNA is transferred to RNA.
DNA uncoils and unzips.
• The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

• Three types of RNA :
A. messenger RNA (mRNA)
B. transfer RNA (tRNA)
C. ribosomal RNA (rRNA)
• Remember: all produced in the nucleus!

• Carries the information for a specific protein .
• Made up of 500 to 1000 nucleotides long.
• Made up of codons ( sequence of three bases)
• Each codon is specific for one amino acid .

mRNA start codon
A U G G G C U C C A U C G G C G C A U A A codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 protein methionine glycine serine isoleucine glycine alanine stop codon aa1
Primary structure of a protein aa2 aa3 aa4 aa5 peptide bonds aa6

• Made up of 75 to 80 nucleotides long.
• Picks up the appropriate amino acid floating in the cytoplasm
• Transports amino acids to the mRNA .
• Has anticodons that are complementary to mRNA codons .
• Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds.

• Made up of rRNA is 100 to 3000 nucleotides long.
• Important structural component of a ribosome.
• Associates with proteins to form ribosomes.

• Large and small subunits.
• Composed of rRNA (40%) and proteins
(60%).
• Both units come together and help bind the mRNA and tRNA.

Large subunit
Small subunit mRNA
A U G C U A C U U C G

• What are the three types of RNA?
• Where is each type produced?
• What is the function of each type of
RNA?

Eukaryotic
Cell
DNA
Nuclear membrane
Transcription
Pre-mRNA
RNA Processing mRNA
Ribosome
Translation
Protein

• Synthesis of proteins in the cytoplasm
• Involves the following:
1.
mRNA (codons)
2.
tRNA (anticodons)
3.
rRNA
4.
ribosomes
5.
amino acids

• In the cytoplasm, translation occurs.
The mRNA binds to a ribosome.
• The strand of mRNA is pulled through the ribosome three bases at a time, in triplets.
• Each of these triplets on the mRNA strand is called a codon.

This is a molecule of messenger RNA.
It was made in the nucleus by transcription from a DNA molecule.
codon
A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

A ribosome on the rough endoplasmic reticulum attaches to the mRNA molecule.
ribosome
A U G G G C U U A A A G C A G U G C A C G U U

Amino acid tRNA molecule
A transfer RNA molecule arrives .
It brings an amino acid to the first three bases (codon) on the mRNA.
anticodon
The three unpaired bases
(anticodon) on the tRNA link up
U A C with the codon.
A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule comes into place, bringing a second amino acid.
Its anticodon links up with the second codon on the mRNA.
U A C
A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule brings the next amino acid into place.
A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond joins the second and third amino acids to form a polypeptide chain.
A U G G G C U U A A A G C A G U G C A C G U U

The process continues.
The polypeptide chain gets longer.
This continues until a termination
(stop) codon is reached.
The polypeptide is then complete.
A U G G G C U U A A A G C A G U G C A C G U U

Transfer RNA (tRNA), reads the strand of mRNA and translates it into a strand of amino acids.
A molecule of tRNA has at one end a set of three bases that will complement the mRNA strand; this is called the anticodon.

• If the 3 base anticodon of the tRNA complements the 3 base codon of the mRNA, they briefly combine.
• The amino acid is left behind when the tRNA leaves.
• As each codon is read, the next tRNA brings in a new amino acid and the polypeptide (protein) chain grows.
• This requires enzymes and ATP.

• The end products of protein synthesis is a primary structure of a protein .
• A sequence of amino acid bonded together by peptide bonds .
aa5 aa4 aa2 aa3 aa199 aa1 aa200

• The protein now has to undergo folding and the addition of bonds
• Folding allows the Protein to reach its 3D
(Tertiary Shape) which influences its
Function.

The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid .
What would be the DNA base code for this amino acid?