Protein Synthesis (5.1.1)

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What is a gene?
A length of DNA which codes for one polypeptide.
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What is a polypeptide?
A polymer made from lots of amino acids joined together by peptide bonds.
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What is a genome?
The entire DNA sequence of an organism.
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Give some examples of what genes code for.
Structural proteins, haemoglobin, muscle proteins, enzymes.
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Why is it useful that the genetic code is universal?
The same triplets code for the same amino acids in almost every kind of organism. This is useful for genetic engineering. We can transfer DNA between organisms of different species and it will still code for the same thing.
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What are the two stages of protein synthesis?
Transcription- the instructions from the genes in the DNA are transferred to mRNA. Translation- mRNA carries the instructions to a ribosome where the polypeptide will be made.
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Describe the process of transcription.
Some DNA unzips- DNA helicase- breaks H-bonds between base pairs. Free RNA nucleotides in nucleus. One of the DNA strands acts as template, free nucleotides line up next to it- complementary base pairing. RNA polymerase joins nct together. mRNA made.
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What happens to the mRNA strand after it's made?
Passes out of the nucleus via a nuclear pore and into the cytoplasm, where it travels to a ribosome.
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What is meant by degenerate code?
There are more codes than necessary to code for the 20 amino acids, so each one has more than one possible triplet code.
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Describe the process of translation.
mRNA held in groove of ribosome, so 6 bases are exposed. tRNA with complementary anticodon to 1st codon binds to it- complementary base pairing. Brings 1st a.a into place. Another tRNA lines up next to 2nd codon, brings 2nd a.a. Peptide bond forms.
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What is the role of the ribosomes?
They are made in the nucleolus and consist of RNA and protein. Made of two sub-units with a groove in between- where the mRNA fits. The ribosome then moves along the mRNA strand reading the triplet code so the a.a can be assembled in the right order.
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What is the role of the tRNA?
Each tRNA molecule is length of RNA folded into hairpin shape- 3 bases exposed at one end- anticodon. Other end of molecule is a site where a particular a.a can bind. In cytoplasm, specific enzymes load specific a.a onto tRNA, using tRNA transferases
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Why is it so important that the primary protein structure is made correctly?
It's the amino acid sequence in the primary structure that determines how the polypeptide folds into secondary and tertiary structures. Any error in primary structure may result in a protein that does not function properly.
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Why would protein synthesis be faster in prokaryotes?
They don't have a nucleus, so transcription and translation both happen in the cytoplasm, which is quicker as they are closer.
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What happens when a STOP codon is reached?
The polypeptide is complete. It's then released into the cytoplasm and this is the primary structure of a protein.
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Describe the process of translation (continued).
Ribosome then shifts along to the next codon. This process is repeated. Once the tRNA have delivered their amino acids and these have been attached, the tRNA returns to cytoplasm, where it can be reused.
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Card 2

Front

What is a polypeptide?

Back

A polymer made from lots of amino acids joined together by peptide bonds.

Card 3

Front

What is a genome?

Back

Preview of the front of card 3

Card 4

Front

Give some examples of what genes code for.

Back

Preview of the front of card 4

Card 5

Front

Why is it useful that the genetic code is universal?

Back

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