1. What determines the amino acid sequence in a polypeptide?
The DNA base sequence, in a way called genetic code.
2. How many bases are there in DNA?
4 types
3. What is a triplet code?
Three consecutive bases in a DNA strand which can code for one amino acid.
4. There are 4 types of bases in DNA. How many triplet codes can be formed?
64
5. What is the meaning of a ‘degenerate’ genetic code?
Within the 64 triplet code, some codes for the same amino acid, these codes are described as degenerate.
6. What are the characteristics among the triplet codes?
(1) Most triplet codes are coding for one particular amino acid.
(2) Some codes act as start signals and stop signals, they do not code for any amino acids.
(3) Some are degenerate codes.
(4) There are no gaps between the triplet codes.
(5) The codes are read in a non-overlapping manner.
(6) The genetic code is universal.
7. What is the meaning of the genetic code being universal?
The same triplet code codes for the same amino acid in all organisms.
8. What is gene expression?
The process when a gene is decoded to make a protein.
9. What are two processes in gene expression?
(1) Transcription: The genetic information in the DNA is copied to the messenger RNA (mRNA).
(2) Translation: the genetic information carried in the mRNA is used to make a polypeptide.
10. How is the process of transcription carried out?
(1) Inside the nucleus, the hydrogen bonds between the two strands of DNA breaks, the DNA unwinds.
(2) One strand of DNA acts as the template strand. It is used to synthesize the mRNA.
(3) Free ribonucleotides are attracted to the template strand through complementary base pairing.
(4) The RNA polymerase catalyses the joining of the adjacent ribonucleotides to form mRNA.
(5) After completion of transcription, the mRNA separates from the template strand of DNA. It then leaves the nucleus through the pores on the nuclear membrane and enters the cytoplasm.
11. What is the name of the DNA strand that is complementary to the template strand?
coding strand
12. What is a codon?
It is located on the mRNA molecule. The three bases which forms the codon on a mRNA is complementary to the triplet code on the DNA.
13. Where does translation occur?
It occurs in the cytoplasm where ribosomes are located.
14. Where are ribosomes located in the cytoplasm?
Most ribosomes are found on the surface of the rough ER, others are found free in the cytoplasm.
15. How is the process of translation being carried out?
(1) mRNA attach to the ribosome
(2) tRNA carries amino acid to the ribosome and binds to the codon
16. What is anticodon?
Located on tRNA, complementary to the mRNA codon and one kind of amino acid.
17. After translation, what will be happen to the polypeptide chain?
Chemical bonding will form between different amino acid on the polypeptide
chain, the chain will be coiled and folded in a specific 3-dimensional structure
called a protein.
18. What is the difference between the polypeptides formed at ribosome on the rough ER and the polypeptides formed at free-floating ribosomes?
On the rough ER: usually are digestive enzymes and hormones, will be transported out of the cells, or be embedded onto the cell membrane.
Free-floating: usually used by the particular cell that they are made in.
19. What is mutation?
The DNA of an organism having sudden and permanent change.
20. According to the level at which mutations occur, what are the two types that mutation is classified into?
(1) Gene mutation
(2) Chromosomal mutation
21. What is gene mutation?
Changes in the base sequence of the DNA.
22. What are the causes of mutation?
(1) deletion
(2) insertion
(3) substitution
(4) inversion
23. What is the cause for sickle-cell anaemia?
A base in the gene that codes for a polypeptide chain on the haemoglobin is substituted, causing the polypeptide chain to have one different amino acid, consequently leading to a change in the 3-D conformation(shape).
24. What is chromosomal mutation?
Change in the structure or the number of chromosome.
25. What are the causes for chromosomal mutation?
(1) Deletion
(2) Duplication
(3) Inversion
(4) Translocation
26. What is the cause of Down symdrome?
Patient having a trisomy (one more) chromosome 21.
27. Why will mutation happen?
(1) It happens spontaneously (randomly happening in nature)
(2) It is induced to happen: by mutagen
28. What are the commonly seen chemical mutagens?
Nitrous acid (Food preservative)
Tar (Cigarette smoke)
Asbestos (Construction materials)
Mustard gas (Chemical warfare)
29. What are the commonly seen radiation mutagen?
(1) UV light (sunlight)
(2) X-ray (medical examination)
(3) Gamma rays (Radiotherapy in treating cancer)