Nucleic acids

Question 1

structure of a nucleotide

Answer 1

nitrogenous base (rectangle), phosphate group (circle), pentose sugar (pentagon)

Question 2

what elements do nucleotides contain?

Answer 2

carbon, hydrogen, oxygen, nitrogen, phosphorus

Question 3

pentose sugar in DNA and RNA

Answer 3

DNA - deoxyribose (one less oxygen atom on bottom right carbon)
RNA - ribose

Question 4

4 bases in DNA

Answer 4

adenine, guanine, cytosine, thymine

Question 5

which 2 bases in DNA have double ring structure and what is the name for them?

Answer 5

adenine and guanine - purines

Question 6

which 2 bases are pyramidines?

Answer 6

cytosine and thymine - single ring structure

Question 7

4 bases in RNA

Answer 7

adenine, guanine, cytosine, uracil

Question 8

how are polynucleotides formed?

Answer 8

phosphate group at carbon 5 of pentose sugar forms covalent bond with hydroxyl group of carbon 3 of another nucleotide
- condensation reaction

Question 9

what is the bond between 2 nucleotides?

Answer 9

phosphodiester bond

Question 10

structure of DNA

Answer 10

• 2 polynucleotide strands held together by hydrogen bonds between complementary bases on opposite strands
• 2 polynucleotide strands are anti-parallel - run in opposite directions
• sugar-phosphate backbone on outside with bases in the centre
• distance between 2 strands is constant the whole way down
• 2 strands form double helix

Question 11

how many bonds are formed between guanine and cytosine?

Answer 11

3 hydrogen bonds

Question 12

how many bonds are formed between thymine and adenine?

Answer 12

2 hydrogen bonds

Question 13

differences between RNA and DNA

Answer 13

• DNA found in chromosomes in nucleus, RNA found in cytoplasm
• DNA is extremely long, RNA is relatively short
• 2 polynucleotide strands in double helix, RNA has only 1 polynucleotide strand

Question 14

Stages of DNA replication

Answer 14

• DNA helicase attaches to DNA molecule causing H bonds between bases to break
• 2 polynucleotides separate
• free nucleotides line up with complementary base on DNA strands
• free activated nucleotides held in place by hydrogen bonds between bases
• DNA polymerase moves down molecule and catalyses formation of phosphodiester bonds between activated nucleotides - condensation reaction
• when phosphodiester bonds form activated nucelotides lose their extra 2 phosphate groups
• as the 2 phophate groups leave, it provides energy for the reaction

Question 15

difference between normal nucleotide activated nucelotide

Answer 15

activated nucleotide contains 3 phosphate groups, normal nucleotide contains 1

Question 16

why is it called semi-conservative replication

Answer 16

• one old strand and one new strand

Question 17

what is a mutation?

Answer 17

an incorrect base is inserted into the growing polynucleotide strand during replication changing the DNA sequence
- random

Question 18

differences between DNA in eukaryotes and prokaryotes

Answer 18

• prokaryotes - circular DNA no free ends, relatively short, not bound to histones
• eukaryotes - linear DNA with 2 ends, much longer, tightly wrapped around histones forming chromosomes

Question 19

transcription

Answer 19

• DNA helicase breaks H bonds between 2 strands of DNA
• complementary free nucleotides form H bonds with bases on exposed nucleotides of one strand
• RNA polymerase moves along template strand and joins RNA nucleotides forming phophodiester bonds
• enzymes move down DNA until they reach the end of the gene
• strand of mRNA formed
• thymine is replaced by uracil
• once mRNA has synthesised, RNA polymerase detaches from DNA and DNA goes back to double helix structure
• mRNA moves out of nucleus through nuclear pore
• prokaryotic cells - mRNA, in eukaryotic cells - pre-mRNA is spliced to get mRNA

Question 20

genome

Answer 20

all the genes in a cell

Question 21

how are mRNA nucleotides read?

Answer 21

as a series of triplets - the genetic code

Question 22

why is the genetic code degenerate?

Answer 22

most amino acids have more than one triplet coding for them

Question 23

what does it mean by the triplet code is non-overlapping?

Answer 23

no base is read more than once

Question 24

what does it mean by the genetic code is universal?

Answer 24

same triplets encode the same amino acids in most organisms on earth

Question 25

translation

Answer 25

• once mRNA moved from nucleus to cytoplasm, a subunit of a ribosome binds to mRNA at start codon
• tRNA molecule with complementary anti-codon to start codon attaches by H bonds between complementary base pairs on anti-codon
• second tRNA molecule attaches with complementary anticodon for second codon on mRNA
• peptide bond forms between 2 amino acids on tRNA’s using ATP - catalysed by enzyme peptidyl transferase (part of ribosomal RNA molecule)
• ribosome moves to next codon and forms peptide bond to next amino acid, first tRNA molecule released
• ribosome continues moving down mRNA forming polypeptide until it reaches a stop codon and is polypeptide chain is released
• multiple ribosomes can be translating one polypeptide chain at once

Question 26

what is a codon?

Answer 26

each triplet in mRNA sequence

Question 27

what is special about a tRNA anticodon?

Answer 27

it’s complementary for the mRNA codon for each specific amino acid

Question 28

what does tRNA do?

Answer 28

a specific amino acid attaches to their attachment site and brings it to the ribosome for translation

Question 29

ATP structure

Answer 29

3 phosphate groups, ribose, adenine
(ATP is a nucleotide)
- adenine and ribose - adenosine

Question 30

how is energy released from ATP?

Answer 30

• not a lot of energy is required to break bond holding last phosphate in place
• breaking bond requires water molecule - hydrolysis
• lots of energy is released when it’s broken

Question 31

hydrolysis of ATP equation

Answer 31

ATP + water —-ATPase—-> ADP + Pi (inorganic phosphate - not attached to carbon molecule) + energy

Question 32

processes using ATP

Answer 32

• active transport, muscle contraction, formation of proteins etc.

Question 33

how are ADP and phosphate recycled back to ATP?

Answer 33

respiration in plant and animal cells
photosynthesis in plant cells
- phosphorylation reaction - catalysed by ATP synthase
- water released - condensation reaction