molecular genetics

Question 1

structure of nucleotides

Answer 1

-consists of pentose sugar, nitrogenous base bonded to 1’ carbon and phosphate group bonded to 5’ carbon

Question 2

pentose sugar

Answer 2

-ribose has a hydroxyl group at 2’ carbon
-deoxyribose has a hydrogen atom at 2’ carbon

Question 3

nitrogenous bases

Answer 3

-purines have 2 rings - adenine and guanine
-pyrimidines have 1 ring - cytosine, thymine and uracil

Question 4

structure of polynucleotides

Answer 4

-many nucleotides joined together to form polynucleotides
-they are joined by strong covalent bonds called phosphodiester bonds
-phosphodiester bonds are formed by condensation reaction
-resulting structure is sugar-phosphate backbone
-5’ end of polynucleotide has phosphate group attached
-3’ end of polynucleotide has hydroxyl group attached

Question 5

structure of DNA

Answer 5

-consists of 2 polynucleotide chains spiralled around an imaginary axis to form a double helix
-chains are antiparallel
-the sugar-phosphate backbones are on the outside of the helix
-the hydrophobic nitrogenous bases are paired in the interior of the helix via complementary base pairing
-adenine pairs with thymine with 2 hydrogen bonds
-guanine pairs with cytosine with 3 hydrogen bonds
-total amount of T + C = total amount amount of A + G

Question 6

function of DNA

Answer 6

-DNA as the genetic material
-each DNA molecule contains numerous genes. each gene is a specific sequence of nucleotides, as part of a DNA molecule, which codes for the synthesis of one specific polypeptide.
-during interphase of a cell cycle, the two strands of DNA separate. each strand serves as a template from which a new complementary strand is made by semi-conservative replication.

Question 7

structure of RNA

Answer 7

-single polynucleotide chain
-adenine pairs with uracil with 2 hydrogen bonds
-guanine pairs with cytosine with 3 hydrogen bonds
-RNA is synthesised by transcription into mRNA, rRNA and tRNA

Question 8

mRNA

Answer 8

-transported to cytoplasm for translation by ribosomes
-used as a template to synthesise proteins

Question 9

rRNA

Answer 9

-enable formation of ribosomes
-ribosomes containing rRNA are the sites of protein synthesis

Question 10

tRNA

Answer 10

-anticodon is present on the tRNA
-anticodon on tRNA forms hydrogen bonds with a codon on mRNA via complementary base pairing
-tRNA transfers the correct type and sequence of amino acid to the ribosome during translation

Question 11

gene expression

Answer 11

-the process by which DNA which carries the genetic code, controls the synthesis of specific polypeptides

Question 12

transcription

Answer 12

-the synthesis of an RNA molecule using one of the DNA strands as a template

Question 13

gene

Answer 13

-a specific sequence of nucleotides, as part of a DNA molecule which codes for the synthesis of one specific polypeptide

Question 14

codon

Answer 14

-three consecutive nucleotide bases in mRNA that codes for a specific amino acid in a protein

Question 15

translation

Answer 15

-the synthesis of protein using mRNA as a template

Question 16

restriction enzyme

Answer 16

-naturally found in bacteria to protect the bacterial cells from other organisms by cutting up foreign DNA
-recognises short specific DNA sequence/ restriction site
-hydrolyse phosphodiester bonds in the sugar-phosphate backbone of DNA strands at specific points within restriction sites
-DNA fragments cut using the same restriction enzyme have complementary sticky ends
-recombined into double-stranded DNA by hydrogen bonds via complementary base pairing

Question 17

DNA ligase

Answer 17

-catalyses formation of phosphodiester bonds between two nucleotides to reattach the sugar-phosphate backbones of DNA strands

Question 18

bacterial plasmids

Answer 18

-function as cloning vectors
-can be induced to enter host cells easily by transformation
-contains restriction enzyme recognition sites
-can replicate autonomously

Question 19

transformation

Answer 19

-the process of introducing the recombinant plasmid into a host cell

Question 20

production of insulin using genetic engineering

Answer 20

-the gene-of-interest coding for insulin from the foreign DNA is cut at a specific restriction site using a specific restriction enzyme. the same specific restriction enzyme is used to cut the same restriction site located in the plasmid.
-recombinant plasmids are formed when complementary sticky ends form hydrogen bonds by complementary base pairing. DNA ligase forms phosphodiester bonds between the DNA fragments of the insulin gene and the plasmid.
-the recombinant plasmids are introduced into bacterial host via transformation. transformed bacterial colonies containing recombinant plasmids are selected depending on the selection markers.
-transformed bacterial cells are cultured in the fermenter, human insulin polypeptide is synthesised inside the bacterial cells.
-insulin polypeptide is harvested by lysing the bacterial cells. insulin polypeptides are then isolated to be incubated under suitable conditions for folding into insulin proteins.
-the insulin protein is purified by crystallisation

Question 21

benefits of genetic engineering

Answer 21

-plant and animal breeders obtain a higher yield and better quality of plant and animal produce

Question 22

issues of genetic engineering

Answer 22

-monopolistic behaviour of biotechnology companies (social)
-reduction in biodiversity, non-target insects get killed (environmental)
-on religious grounds, tampering with nature and go against the natural way of life (ethical)

Question 23

cloning

Answer 23

-nucleus removed from a donor egg cell
-enucleated egg was placed next to diploid cell, then shocked to fuse
-fused cell shocked again to start cell division
-cell division continue for several days to form an embryo before being implanted into surrogate mother