Nucleic acids

Question 1

Nucleotides

Answer 1

-monomers of nucleic acids: DNA, RNA
-contain phosphate group, pentose sugar (deoxyribose/ ribose) and nitrogenous base

Question 2

Structure of DNA

Answer 2

-polymer made up of monomers nucleotides
-molecule of DNA consists of 2 polynucleotide strands
-two strands are anti parallel
-phosphodiester bond between sugar and phosphate
-hydrogen bonds between two bases holding the 2 strands together
-adenine pairs with thymine by 2 hydrogen bonds
-guanine pairs with cytosine by 3 hydrogen bonds
-double helix
-sugar phosphate backbone

Question 3

Types of nucleotide

Answer 3

-pyrimidines -Thymine, cytosine (1 ring)
-purines- adenine, guanine (2 rings)

Question 4

Extraction and purification of DNA

Answer 4

-macerate tissue (kiwi/strawberry) with pestle and mortar to break cell wall
-add washing up liquid to disrupt membrane
-add ethanol so DNA precipitates

Question 5

DNA replication

Answer 5

-double helix is untwisted by gyrase enzyme
-then unzipped by DNA helicase which breaks H bonds between bases
-free nucleotides are bonded to exposed bases
-DNA polymerase catalyses addition of new nucleotides in 5’ to 3’ direction
-leading stand synthesised continuously, lagging strand synthesised in okazaki fragments which are join by enzyme ligase
-is semi conservative as it creates 2 new molecules of DNA each containing one original strand

Question 6

RNA structure differences from DNA

Answer 6

-ribose not deoxyribose
-base uracil which replaces thymine
-usually single stranded and shorter
-3 forms mRNA, tRNA, rRNA

Question 7

Nature of genetic code

Answer 7

-universal as in almost all organisms the same triplet code, codes for the same amino acid
-degenerate for most amino acids, there’s more than one triplet code to reduce effect of mutations
-non overlapping so no bases are missed

Question 8

Protein synthesis

Answer 8

Transcription
-gene unwinds an unzips
-H bonds between bases break
-RNA polymerase catalyses formation of temporary H bonds between RNA nucleotides and DNA bases (template strand)
-length of RNA complementary to DNA is produced and a copy of the other DNA strand (coding strand)
-mRNA passes out nuclear envelope to ribosome
Translation
-tRNA molecules bring amino acids and find their place when the anticodon binds temporarily to complementary codon on mRNA
-peptide bonds between amino acids form
-after polypeptide is assembled, mRNA breaks down and can be recycled into new lengths of mRNA
-new polypeptide folds into correct tertiary structure for its function

Question 9

Codon-
Anticodon-

Answer 9

-triplet of bases on mRNA
-triplet of bases on tRNA complementary to mRNA codon