Nucleotides and nucleic acids

Question 1

Describe the structure of a nucleotide?

Answer 1

• phosphate group
• pentose sugar
• ribose base

Question 2

Name the pentose sugars in DNA and RNA?

Answer 2

DNA = deoxyribose
RNA = ribose

Question 3

What is the difference between ribose and deoxyribose?

Answer 3

Ribose has a hydroxyl (OH) group at position 2 whereas deoxyribose has a hydrogen atom (H) there

Question 4

How are polynucleotide strands formed and broken down?

Answer 4

• formed through condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
• broken down by hydrolysis reactions using a molecule of water

Question 5

Describe the structure of DNA?

Answer 5

• 2 deoxyribose polynucleic strands arranged in a double helix with 2 sugar-phosphate backbones
• H bonds form between complementary base pairings on the strands (AT,GC)

Question 6

Name the purine bases and describe there structure?

Answer 6

• adenine and guanine
• 2 ring structures

Question 7

Name the pyrimidine bases and describe there structure?

Answer 7

• thymine, cytosine and uracil
• 1 ring structures

Question 8

Name the complementary base pairs in DNA and RNA and describe there hydrogen bonding?

Answer 8

DNA - 2 H bonds between adenine and thymine
RNA - 2 hydrogen bonds between adenine and uracil
Both - 3 hydrogen bonds between guanine and cytosine

Question 9

Why is DNA replication semi conservative?

Answer 9

• strands from original DNA molecule act as a template
• new DNA molecules contain 1 old strand and one new strand
• specific base pairing enables genetic material to be conserved accurately

Question 10

Explain the role of DNA helicase in semiconservative DNA replication?

Answer 10

Breaks H bonds between complementary base pairs to form 2 single strands which can act as templates

Question 11

How is a new strand formed by semiconservative DNA replication?

Answer 11

• free nucleotides attach to exposed bases by complementary base pairing
• DNA polymerase joins adjacent nucleotides on new strands in a 5’ to 3’ direction via condensation reactions to form phosphodiester bonds
• H bonds reform

Question 12

Identify the features of the genetic code?

Answer 12

• non-overlapping (each triplet is only read once)
• degenerate (more than one triplet codes for the same amino acids)
• universal (same bases and sequences used by all species)

Question 13

How does a gene determine the sequence of amino acids in a protein?

Answer 13

consists of base triplets that code for a specific amino acid

Question 13

What does transcription produce and where does it occur?

Answer 13

• produces mRNA
• occurs in the nucleus

Question 13

Outline the process of DNA transcription?

Answer 13

• RNA polymerase binds to promoter region on a gene
• section of DNA uncoils into 2 strands with exposed bases, antisense strand acts as a template
• free nucleotides are attracted to their complementary bases
• RNA polymerase joins adjacent nucleotides to form phosphodiester bonds

Question 13

What’s the difference between the sense and antisense strand?

Answer 13

Sense strand = provides the code to make a protein when read in the right direction

Antisense strand = non-coding strand that serves as a template for RNA synthesis

Question 14

What happens after a strand of mRNA is transcribed?

Answer 14

• RNA polymerase detaches at a terminator region
• H bonds reform and DNA rewinds
• splicing removes introns from pre-mRNA in eukaryotic cells
• mRNA moves out of the nucleus via nuclear pores and attaches to ribosomes

Question 15

What are introns and exons?

Answer 15

introns = intervening non-coding regions of a gene

exons = coding regions of a gene

Question 16

What does translation produce and where does it occur?

Answer 16

• produces proteins
• occurs in cytoplasm on ribosomes (made of protein and rRNA)

Question 17

Outline the process of translation?

Answer 17

• ribosomes move along the mRNA until “start” codon
• tRNA anticodons attach to complementary bases on mRNA
• condensation reactions between amino acids on tRNA form peptide bonds (requiring energy from ATP hydrolysis)
• process continues to form polypeptide chains until “stop” codon is reached

Question 18

What is mRNA?

Answer 18

mRNA = (messenger RNA) is a single strand of RNA made from a DNA template that carries a genetic sequence to the ribosomes that read by a ribosome in the process of synthesizing a protein

Question 19

What is tRNA?

Answer 19

tRNA = (transfer RNA) is a small RNA molecule that helps decode a mRNA sequence into a protein

Question 20

What is rRNA?

Answer 20

rRNA = (ribosomal RNA) is a part of the ribosome that reads the order of amino acids and builds proteins through protein synthesis

Question 21

Describe the structure of ATP and ADP?

Answer 21

Both = nucleotide derivatives of adenine
ATP = has three inorganic phosphate groups
ADP = has 2 inorganic phosphate groups

Question 22

What is a mutation?

Answer 22

An alteration to the DNA base sequence often arising spontaneously during DNA replication