DNA

Question 1

Nucleotide.

Answer 1

• Organic nitrogenous base. (Adenine, thymine/ uracil, guanine, cytosine).
• Pentose sugar. (Deoxyribose/ ribose).
• Phosphate group.
• Monomer of nucleic acid/ polynucleotide.

Question 2

Structure of DNA.

Answer 2

• Polymer, made up of monomers (nucleotides).
• 2 DNA strands - anti-parallel to each other. - sugar-phosphate backbone.
• Complementary base pairing. - A+T , G+C. (Purine to pyrimidine).

Question 3

Formation of polynucleotides.

Answer 3

• Nucleotides linked together by condensation reaction.
• Phosphate group at 5th carbon of pentose sugar of one nucleotide forms covalent bond with hydroxyl group at 3rd carbon of pentose sugar of adjacent nucleotide.
• Forms a phosphodiester bond (covalent).
• Broken by hydrolysis.

Question 4

Purine and pyrimidine.

Answer 4

Purine = Bigger + has 2 carbon rings.
- Adenine and Guanine.
Pyrimidine = Smaller.
- Thymine, uracil and cytosine.

Question 5

Extracting DNA.

Answer 5

• Chop kiwi into pieces + mash up with stirring rod in a boiling tube. (Brakes cell walls + membrane).
• Add salt. (Breaks proteins holding together DNA strands).
• Add washing up liquid. (Breaks phospholipid bilayer/ cell membrane).
• Leave in water bath at 60 degrees for 10 minutes. (Denatures proteins in bilayer).
• Drain contents through filter + muslin. (Removes larger solids).
• Leave in a beaker of ice cubes for 5 minutes. (Returns to room temperature - easier to precipitate).
• Pour layer of ethanol on top, DNA will float out of mixture. (Allows DNA to precipitate).

Question 6

DNA replication.

Answer 6

• DNA helicase breaks the hydrogen bonds between the 2 polypeptide DNA strands.
• The helix unzips to form 2 DNA strands.
• Each original strand acts as a template.
• Free floating DNA nucleotides join to the exposed bases on each original template strand by complementary base pairing. (A to T, G to C, Purine to pyrimidine).
• The nucleotides on the new strand are joined together by the enzyme DNA polymerase.
• This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand.
• The strand recoils to form a double helix. Each new molecule contains one strand of the original DNA and one new strand.
• This type of replication is semi-conservative replication because half of the strands in each new DNA molecule are from the original piece of DNA.

Question 7

Types of RNA.

Answer 7

• Messenger RNA.
• Transfer RNA.
• Ribosomal RNA.

Question 8

mRNA.

Answer 8

• Messenger RNA.
• Single polynucleotide strand, copy of one gene.
• Made in the nucleus during transcription.
• Carries genetic code from DNA in nucleus to cytoplasm as DNA is too big to fit through the nuclear pores.
• Used to make protein during transcription.
• Groups of 3 adjacent bases = Codon. - Codes for amino acid.

Question 9

tRNA.

Answer 9

• Transfer RNA.
• Single polynucleotide strand folded into clover shape.
• Hydrogen bonds between specific base pairs hold together.
• Every tRNA has a specific sequence of bases at one end called an Anti-codon.
• Amino acid binding site at other end.
• Found in cytoplasm.
• Involved in translation.
• Carries amino acids.

Question 10

rRNA.

Answer 10

• Ribosomal RNA.
• 2 subunits in each ribosome, along with proteins.
• Ribosome moves along mRNA strand along proteins.
• rRNA in ribosome catalyses the formation of peptide bonds between amino acids is translation.

Question 11

Protein synthesis.

Answer 11

1. Transcription.
2. Translation.

Question 12

Transcription.

Answer 12

• RNA polymerase attaches to the DNA molecules at the start of a gene. (start codon).
• The H bonds between the two strands break, the DNA uncoils.
• One strand is used as a template strand to make an mRNA copy of the other strand.
• The RNA polymerase now lines up free floating, complementary RNA nucleotides along the template strand.
• Once the RNA nucleotides have paired up with the bases on the DNA template strand they are paired together to form the mRNA strand.
• RNA polymerase moves along the DNA, separating the DNA and mRNA.
• The H bonds between the DNA strand reform once the RNA polymerase has passed, the double helix reforms.
• When RNA polymerase reaches the stop codon, the mRNA stops being produced and completely separates from the DNA.
• The mRNA moves out of the nucleus through a nuclear pore.
• Once in the cytoplasm it attaches to a ribosome.

Question 13

Translation