Ocr As Biology - Genes And Protein Synthesis

Front 1

Define the term 'gene'.

Back 1

A gene is a sequence of DNA nucleotides that codes for a polypeptide.

Front 2

What two factors can be different when looking at different proteins?

Back 2

• The different number of amino acids.
• The different order of amino acids.
  

Front 3

What determines the order of amino acids in a particular protein?

Back 3

• The order of nucleotide bases in a gene.

Front 4

How many bases make up an amino acid? What is another name for this structure?

Back 4

A sequence of three bases (called a triplet) in a gene.

Front 5

Give an overview of protein synthesis.

Back 5

• DNA molecules are found in the nucleus of a cell, but the organelles that make proteins (ribosomes) are found in the cytoplasm.
• DNA is too large to move out of the nucleus, so a section is copied into mRNA. This is called transcription.
• The mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where is can be used to create a protein. This is called translation.

Front 6

Name the three main types of RNA.

Back 6

• Messanger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)

Front 7

Where is the messenger RNA created?

Give details on the bases it carries.

What is its job?

Back 7

• It is made in the nucleus.
• It has three adjacent bases called a codon.
• It carries the genetic code from the DNA in the nucleus to the cytoplasm, where it's used to make a protein during translation.

Front 8

Where is transfer RNA found?

Describe it's structure.

What is its job?

Back 8

• Found in the cytoplasm.
• It has an amino acid binding site at one end and a sequence of three bases at the other end called an anticodon.
• It carries the amino acids that are used to make proteins to the ribosomes during translation.

Front 9

What is ribosomal RNA's affect on a ribosome (in terms of structure)? What is its job?

Back 9

• It causes the two sub-units in ribosomes (along with proteins) [see picture].
• The ribosome moves along the mRNA strand and helps catalyse the formation of peptide bonds between the amino acids.

Front 10

What are codons and anticodons sometimes referred as?

Back 10

Triplets.

Front 11

What is the 'genetic code'?

Back 11

It is the sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids.

Front 12

Give an overview of how genetic code is read.

Back 12

• Each base triplet is read in sequence, separate from the codon before it and after it.
• The codons do not share bases - the code is non-overlapping. This means each codon codes for itself and does not share bases with any over codons.

Front 13

Genetic code is degenerate - define the term 'degenerate' (in terms of biology). What does this lead to?

Back 13

• This means there are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets!).
  
• This means some amino acids can be coded for by more than one codon combination (e.g. tyrosine can be coded for UAU or UAC).

Front 14

Some triplets can be used to signal the start and end of protein production, what are these triplets called? Give an example of one of these triplets.

Back 14

• Start and stop codons
• UAG is a stop signal

Front 15

The genetic code is universal - what does this mean?

Back 15

The same specific base triplets code for the same amino acids in all different things (e.g. UAU codes for tyrosine in all organisms).