Exercise 3 Flashcards
1
Q
- How do proteins differ from one another, and what does this difference mean to the function of a protein? Name some common structural proteins found in the body.
A
- Proteins differ from one another in the number and order of their amino acids. The sequence of amino acids in a protein leads to its particular shape, and the shape of a protein helps determine its function. Some common structural proteins are hemoglobin, antibodies and actin and myosin filaments found in muscle cells. Enzymes which we have studied in earlier modules are also proteins.
2
Q
- What is a gene? What is a codon? What is an anti-codon?
A
- A gene is a segment (short section) of DNA that codes for a protein.
A codon is a triplet (3 nitrogen containing bases in sequence) that represents one amino acid (refer to Table 19.7 on page 372). Codons will be found in mRNA molecules.
An anti-codon is the complementary triplet (according to base pairing) that will be found in tRNA molecules.
3
Q
- What are the two steps involved in gene expression?
A
- The two steps involved in gene expression are transcription which involves making an exact copy of the genetic information, and translation which refers to converting this information into a protein.
4
Q
- Define transcription. Briefly describe the events that take place during transcription.
A
- Transcription is the process whereby a DNA strand serves as a template for the formation of mRNA. During transcription a section of the DNA molecule (gene) unzips into two separate strands. A strand of mRNA forms that is complementary to one of the strands of the DNA molecule. The end result is a molecule of mRNA that contains triplet codons, each of which represents the same amino acids as the original triplet found on the DNA.
5
Q
- What happens to the mRNA once it is processed?
A
- Once processed the mRNA strand leaves the nucleus of the cell, enters the cytoplasm and then associates itself with the ribosomes.
6
Q
- Define translation. Briefly describe the events that take place during translation.
A
- Translation is the process whereby ribosomes use the sequence of codons in mRNA to produce a polypeptide with a particular sequence of amino acids. During translation tRNA molecules bring amino acids that they have located in the cytoplasm to the ribosomes. Usually there is more than one tRNA molecule for each of the 20 possible amino acids. The amino acid binds to one end of the molecule. At the other end of each tRNA is a specific anticodon that will eventually pair with a codon of the mRNA in the order directed by the sequence found on the mRNA
7
Q
- What are the three steps involved in the building of a polypeptide?
A
- The three steps involved in polypeptide synthesis are:
i) initiation
ii) elongation iii)termination
8
Q
- Initiation – mRNA binds to the smaller of the two ribosomal subunits; then the larger subunit associates with the smaller one
Elongation – the polypetide lengthens one amino acid at a time.
Termination – the end of synthesis occurs at a specific codon than means stop. The ribosome will then split into its two subunits and detach from the mRNA molecule.
A
- Initiation – mRNA binds to the smaller of the two ribosomal subunits; then the larger subunit associates with the smaller one
Elongation – the polypetide lengthens one amino acid at a time.
Termination – the end of synthesis occurs at a specific codon than means stop. The ribosome will then split into its two subunits and detach from the mRNA molecule.
9
Q
- What is a polyribosome and how do they function in protein synthesis?
A
- A polyribosome refers to several ribosomes simultaneously moving along one mRNA molecule at a time during the process of translation in protein synthesis.
10
Q
- What are the sub-units of proteins? How many sub-units are there?
A
- The sub-unit of a protein is an amino acid. There are 20 different amino acids.
