5.3.2 Polypeptide Synthesis

Question 1

Function and Importance

Answer 1

Forms appropriate polypeptides and therefore proteins, which are fundamental to all cell structures and functioning.

• Proteins control all aspects of cellular life

Without protein synthesis, genetic material would be unable to manifest in observable, functioning characteristics.

Question 2

Protein Synthesis

Answer 2

Protein synthesis is the process is which polypeptide chains are formed from coded combinations of single amino acids inside the cell.

The synthesis of new polypeptides requires a coded sequence, enzymes, and RNAs (messenger, ribosomal, transfer). Protein synthesis takes place within the nucleus and ribosomes of a cell and is regulated by DNA and RNA.

1. Transcription
2. Translation
3. Golgi Apparatus for assembling and packaging into a protein

Question 3

mRNA (Messenger RNA)

Synthesis Terminology

Answer 3

conveys genetic material from DNA to ribosome during translation, meaning it must be accurate for the correct polypeptide chain to form, making it critical to both transcription and translation

Question 4

Codon

Synthesis Terminology

Answer 4

groups of three nucleotides that are read during translation to specify an amino acid, or whether to start/stop the production of a polypeptide chain

Question 5

tRNA (Transfer RNA)

Synthesis Terminology

Answer 5

responsible for decoding the mRNA in the ribosome using codons in translation and carrying the complementary anticodon

Question 6

Protein

Synthesis Terminology

Answer 6

complex macromolecules made of one or more polypeptide chains and containing chemical elements (carbon, hydrogen, oxygen, nitrogen)

Structures:

• Primary Structure - sequence of amino acids in polypeptide chain
• Secondary Structure - folding of polypeptide chain into a specific shape (e.g. alpha helices, beta sheets)
• Tertiary Structure - further folding of the chain and interactions of the side chains
• Quaternary Structure - interaction of protein subunits (polypeptide chains)

Types:

• Fibrous Proteins - form long and insoluble structural components of cells and tissues
• Globular Proteins - form compact, soluble and spherical structures that often transport proteins (e.g. haemoglobin)

Question 7

Transcription

Answer 7

Genetic information is transcribed from DNA to RNA in the nucleus

• A section of DNA (a gene) unzips via enzymes
• A single strand of the unzipped DNA is exposed, allowing it to act as a template for free-floating RNA nucleotides to join with their corresponding pairs
• mRNA forms as RNA polymerase joins the RNA nucleotides, which will then detach and leave the nucleus
• DNA rezips

Question 8

Translation

Answer 8

Synthesis of amino acid polypeptide sequence in the cytoplasm’s free ribosome or on the rough ER

• mRNA goes into the ribosome and the ribosome arranges the strand into codons
• Corresponding tRNA carrying an anticodon bring an amino acid (which float in the cytoplasm) with each triplet of bases coding for a particular amino acid to be picked up by tRNA
• Ribosome reads codons and amino acids deposit into a chain of amino acids (polypeptide) until the ribosome reads the ‘stop’ codon