7.3 DNA Translation

Question 1

Outline the process of translation

Answer 1

mRNA leaves nucleus and enters the cytoplasm where it interacts with a ribosome.

Initiation
1. small ribosomal sub units binds to start codon of mRNA.
2. large ribosomal subunit attaches itself to complete the translation complex.

Elongation
1. tRNA binds to A site in large ribosomal sub unit, carrying a complementary amino acid coded by the anticodon of tRNA that is complentary to the codon on the mRNA strand.

2. ribosome translocates along the mRNA moving the first tRNA into the P site.
3. then a new tRNA with a corresponding amino acid joins the A site like previously.
4. In the P site the two amino acids of the tRNA are joined by a polypeptide bond.
5. the ribosome translocates again, moving the second tRNA into the P site, where it’s amino acid is binded to the new amino acid by a peptide bond and the first tRNA into the E site, where it detaches and leaves the ribosome.
6. the process continues, building a polypeptide chain in the process

Termination¨
1. ribosome reaches the termination codons: UAG, UAA or UGA
2. a release factor binds in the A site and causes the disassembly of the components of the translation complex.

Question 2

State the difference between free and bound ribosomes

Answer 2

Free ribosomes are located in the cytoplasm and produce proteins for a cell

Bound ribosomes are attached to the endoplasmic reticulum and produce proteins that are transported out of the cell

Question 3

Describe the primary structure of a protein including type of bonding

Answer 3

sequence of amino acids which comprise the polypeptide chain

-covalent peptide bonds between the amine and carboxyl groups of adjacent amino acids.

Question 4

Describe the secondary structure of a protein. Refer to diagram

Answer 4

way a polypeptide folds in a repeating arrangement to form α-helices and β-pleated sheets

• This folding is a result of hydrogen bonding between the amine and carboxyl groups of non-adjacent amino acids
• In pictures, alpha helices are represented as spirals (purple ; left) and beta-pleated sheets as arrows (blue ; right)

Question 5

Describe tertiary protein structure

Answer 5

the polypeptide chain coils and turns to form a complex molecular shape (i.e. the 3D shape)

• caused by interactions between R groups; including H-bonds,

Tertiary structure may be important for the function of the protein (e.g. specificity of active site in enzymes)

Question 6

Describe the quaternary structure of protein

Answer 6

Multiple polypeptides interact to form a single, larger protein

Quaternary structures may be held together by a variety of bonds (similar to tertiary structure)

Question 7

Differentiate between fibrous and globular proteins

Answer 7

Fibrous protein: generally composed of long and narrow strands and have a structural role (they are something)

Globular proteins generally have a more compact and rounded shape and have functional roles (they do something)

Question 8

Which ribosomes are eukaryotic and which prokaryotic

Answer 8

70s : prokaryotes (smaller)
80s: eukaryotic (larger)

Question 9

List example species for which the entire genome has been sequenced

Answer 9

Rice, yeast, fruit fly, human