Unit 1 Key Area 3

Genetic composition of a cell

By the sequence of DNA bases in its genes

Involves the transcription and translation of DNA sequences. A gene is a section of DNA which codes for a protein. Only a fraction of genes in a cell are expressed.

The structure, shape and function of the protein produced.

Guanine, Adenine, Uracil and cytosine

• messenger RNA (mRNA) • ribosomal RNA (rRNA) • transfer RNA (tRNA)

• Occurs in the Nucleus • RNA unwinds and breaks bonds between bases in the two DNA strands • RNA polymerase can only add nucleotides to the 3’ end of the newly synthesised mRNA transcript • RNA polymerase adds complementary RNA nucleotides to make a primary transcript Introns removed and exons spliced together to make mature mRNA (in a process called RNA splicing) -

• Occurs in the Nucleus • RNA unwinds and breaks bonds between bases in the two DNA strands • RNA polymerase can only add nucleotides to the 3’ end of the newly synthesised mRNA transcript • RNA polymerase adds complementary RNA nucleotides to make a primary transcript Introns removed and exons spliced together to make mature mRNA (in a process called RNA splicing) -

• 1st binds to mRNA • 2nd side binds to ribosome • 3rd side binds to a specific amino acid • 4th side binds to enzymes controlling the process

rRNA and proteins

introns

Exons are coding regions and are spliced together to form a mature transcript of mRNA

1) mRNA binds to a ribosome. Translation begins at a start codon. 2) Each tRNA binds to a specific amino acid in the cytoplasm and carries it to the ribosome. 3) Each tRNA anticodon binds to a complementary codon of mRNA lining up the amino acids in a specific order, translating the genetic code into a sequence of amino acids. 4) Peptide bonds form between the amino acids creating a growing polypeptide chain. 5) Each tRNA then leaves the ribosome as the polypeptide forms 6) Translation ends at a stop codon 7) when the polypeptide chain is complete it detaches from the ribosome.

Carbon Hydrogen Oxygen Nitrogen Sometimes sulfur

Each protein is made from amino acids linked by peptide bonds to form polypeptide chains

The sequence of DNA bases

The sequence of amino acids

Enzymes Structural Proteins Hormones Antibodies