2.1.3 - Nucleotides and Nucleic Acids

Question 1

What is a nucleic acid?

Answer 1

a polymer of nucleotides

Question 2

What are nucleotides?

Answer 2

the monomers that makes up nucleic acids

Question 3

What is a nucleotide made up of? (its basic structure)

Answer 3

a phosphate group
a pentose sugar
a nitrogenous base

Question 4

Which pentose sugar is found in DNA?

Answer 4

deoxyribose

Question 5

Which pentose sugar is found in RNA?

Answer 5

ribose

Question 6

What nitrogenous bases are found in DNA?

Answer 6

adenine (A)
thymine (T)
guanine (G)
cytosine (C)

Question 7

What nitrogenous bases are found in RNA?

Answer 7

adenine (A)
uracil (U)
guanine (G)
cytosine (C)

Question 8

What are pyrimidines?

Answer 8

smaller bases which contain a single carbon ring structure
-cytosine, thymine(/uracil)

Question 9

What are purines?

Answer 9

larger bases which contain double carbon ring structure
-adenine, guanine

Question 10

What covalent bond is formed between nucleotides?

Answer 10

phosphodiester bond

Question 11

What happens when two nucleotides join?

Answer 11

-condensation reaction
-phosphodiester bond formed
-phosphate group (C5) of one nucleotide joins with the hydroxyl group (C3) of the pentose of another nucleotide

Question 12

What are the base pairing rules?

Answer 12

1) A always pairs with T/U
G always pairs with C
2) 2 hydrogen bonds form between A and T/U
3 hydrogen bonds form between C and G
3) Pyrimadines (C, T, U) always pair with purines (A, G)

Question 13

What is the structure of DNA?

Answer 13

-2 strands of polynucleotides coiled into a double helix
-held together by hydrogen bonds between bases
-strands run in opposite directions, making them antiparallel (3->5 and 5->3)

Question 14

What are the differences between DNA and RNA?

Answer 14

-pentose sugars -deoxyribose in DNA and ribose in RNA
-RNA has a uracil base where DNA has a thymine base
-DNA is double stranded but RNA is single stranded

Question 15

What are the similarities between DNA and RNA?

Answer 15

-both have nucleotides as their monomer
-both have A, C and G bases
-both have phosphodiester bonds

Question 16

Why is DNA replication semi-conservative?

Answer 16

the replicated DNA contains one newly formed strand and one original strand (which acts as a template)

Question 17

What happens in DNA replication?

Answer 17

-DNA double helix unwinds (by DNA gyrase)
-the H-bonds between bases are broken (by DNA helicase)
-free activated DNA nucleotides complementary base pair to exposed bases
-DNA polymerase forms phosphodiester bonds between nucleotides

Question 18

What does the enzyme DNA gyrase do?

Answer 18

unwinds the DNA double helix

Question 19

What does the enzyme DNA helicase do?

Answer 19

breaks hydrogen bonds between bases

Question 20

What does the enzyme DNA polymerase do?

Answer 20

catalyses formation of phosphodiester bonds between nucleotides (forming sugar phosphate backbone)

Question 21

What is the leading strand in DNA replication?

Answer 21

the strand that is unzipped (by DNA polymerase) from the 3’ end -so is continuously replicated (undergoes continuous replication)

Question 22

What is the lagging strand in DNA replication?

Answer 22

the strand that is unzipped (by DNA polymerase) from the 5’ end (meaning DNA polymerase has to wait for a section to be unzipped and then work back along the strand) so undergoes discontinuous replcation
-in the lagging strand, the DNA is produced in sections (okazoki fragments) which DNA ligase joins together

Question 23

What does the enzyme DNA ligase do?

Answer 23

joins the Okazoki fragments in discontinuous replication together

Question 24

What is genetic code?

Answer 24

the sequence of bases in DNA, which acts as an instruction for the order of amino acids (ie the primary structure of a protein) when proteins are being produced

Question 25

What is a codon?

Answer 25

a three base sequence of DNA/RNA -each codon codes for an amino acid

Question 26

What are the two stages of protein synthesis?

Answer 26

transcription (base sequences are copied and transported to ribosomes) translation (complementary code is decoded by tRNA into primary structure of protein)

Question 27

What is the sense strand in protein synthesis?

Answer 27

DNA strand containing correct code to be synthesised

Question 28

What is the antisense strand in protein synthesis?

Answer 28

the complementary copy of the sense strand (doesn't code for protein but acts as template to produce DNA like the sense strand)

Question 29

What happens in transcription?

Answer 29

-DNA double helix is unwound and unzipped (H-bonds are broken) -antisense strand acts as template strand -free RNA nucleotides pair with complementary pairs on exposed antisense strand -DNA polymerase forms phosphodiester bonds between RNA nucleotides -mRNA leaves nucleus through pore in nuclear envelope (to travel to ribosome) -double helix reforms

Question 30

What happens in translation?

Answer 30

-mRNA binds to ribosome at its start codon -tRNA's anticodon binds to a codon on mRNA (max 2 can at one time) -peptide bond forms between amino acids on tRNA molecules (this is catalysed by peptidyl transferase) -ribosome moves along mRNA and the tRNA from the first codon is released, leaving its amino acid attached to the next amino acid -process continues (so a polypeptide chain forms) until the ribosome reaches the stop codon and the polypeptide chain is released

Question 31

What does ATP supply energy for?

Answer 31

-synthesis -transport -movement

Question 32

What is ATP made up of? (its structure)

Answer 32

-ribose sugar -adenine (nitrogenous base) -three phosphate groups

Question 33

Why is ATP a good energy source?

Answer 33

-small -water soluble -releases energy in small quantities -easily regenerated

Question 34

Describe the procedure for extracting DNA

Answer 34

-grind sample -mix with detergent -add salt -place in hot water bath -add protease -add layer of ethanol

Question 35

Why do you grind the sample in DNA extraction?

Answer 35

to break cell walls so that detergent can get inside cells

Question 36

Why do you mix with detergent in DNA extraction?

Answer 36

breaks cell membranes so that cell contents are released into the detergent

Question 37

Why do you add salt in DNA extraction?

Answer 37

breaks H-bonds between DNA bases and water

Question 38

Why do you place in hot water bath in DNA extraction?

Answer 38

stops enzymes from breaking DNA down

Question 39

Why do you add protease in DNA extraction?

Answer 39

breaks histamines in DNA down

Question 40

Why do you add a layer of ethanol in DNA extraction?

Answer 40

DNA doesn't dissolve in alcohol so will precipitate