Chapter 3 - Nucleotides and Nucleic Acids

Question 1

What are the two types of nucleic acids?

Answer 1

DNA and RNA

Question 2

What is a nucleotide made up of?

Answer 2

5 Carbon deoxyribose sugar
Nitrogenous base
Phosphate group

Question 3

What is a nucleic acid?

Answer 3

A large polymer formed from many nucleotides linked together in a chain

Question 4

How are nucleotides linked together?

Answer 4

Condensation reaction
Phosphodiester bond between the phosphate group of one nucleotide and the hydroxyl group of the sugar

Question 5

What does DNA stand for?

Answer 5

Deoxyribonucleic acid

Question 6

What are the five different nitrogenous bases?

Answer 6

Adenine (A), Guanine (G), Cytosine (C) and Thymine (T), Uracine (U)

Question 7

What is a pyrimidine?

Answer 7

The smaller bases which contain single carbon rings (Thymine and Cytosine)

Question 8

What is a purine?

Answer 8

The larger bases which contain double carbon rings structures (Adenine and Guanine)

Question 9

Which bases bond with each other and with how many hydrogen bonds?

Answer 9

Thymine and Adenine (2 Hydrogen bonds)
Cytosine and Guanine (3 Hydrogen bonds)

Question 10

What two enzymes are involved in DNA replication?

Answer 10

Helicase and polymerase

Question 11

What does helicase do?

Answer 11

Unwinds the double helix and separates the two strands

Question 12

What does polymerase do?

Answer 12

Builds the new strand by forming new phosphodiester bonds between nucleotides

Question 13

How do mutations occur?

Answer 13

If a base sequence is not matched correctly

Question 14

Describe DNA

Answer 14

Double stranded molecule that forms a double helix
Nucleotide that holds genetic information
Strands are anti-parallel running in opposite directions

Question 15

Describe the structure of an RNA nucleotide

Answer 15

Ribose sugar
Phosphate group
Nitrogenous bases

Question 16

Describe RNA

Answer 16

Short single stranded molecule used on protein synthesis

Question 17

What are nucleotides?

Answer 17

Monomers which form nucleic acids; like DNA and RNA

Question 18

Which nitrogenous bases are complementary to each other in DNA?

Answer 18

Thymine and Adenine
Guanine and Cytosine
(Always a purine and pyrimidine base paired together)

Question 19

Which nitrogenous bases are complementary to each other in RNA?

Answer 19

Uracil and Adenine
Guanine and Cytosine
(Always a purine and pyrimidine base paired together)

Question 20

Why is it important for a purine and pyrimidine to pair together?

Answer 20

To help maintain the order of the genetic code when DNA replicates

Question 21

What is ATP?

Answer 21

Adenine triphosphate
Composed of adenine, ribose and 3 inorganic phosphate groups

Question 22

Why is ATP important?

Answer 22

Essential for metabolism
3 phosphate ions play significant role in energy transfer
Immediate source of energy for biological processes

Question 23

How is ATP formed?

Answer 23

Made during respiration via a condensation reaction using ATP synthase
ADP + Pi -> ATP + H2O
Pi = inorganic phosphate group

Question 24

How is ATP broken down?

Answer 24

Hydrolysed using ATP hydrolase
ATP + H2O -> ADP + Pi
Releases small amount of energy breaking the bond between one of the phosphate groups
Pi = inorganic phosphate group

Question 25

What is ADP?

Answer 25

Adenine diphosphate

Question 26

How does DNA structure relate to its function?

Answer 26

Stable structure - due to sugar-phosphate backbone and the double helix Double stranded - easy replication using opposite strand as a template Weak hydrogen bonds between bases - low energy required to separate the strands during replication Large molecule - carries a lot of information Complimentary bases - allows identical copies to be made

Question 27

What are the three types of RNA?

Answer 27

mRNA - messenger RNA tRNA - transfer RNA rRNA - ribosomal RNA

Question 28

What is rRNA?

Answer 28

Main bulk of ribosome structure

Question 29

What is mRNA?

Answer 29

Copy of one gene from DNA Created in nucleus, leaves via nuclear pore which is carried to a ribosome in cytoplasm or RER Shorter than DNA Short-lived (can be easily broken down by enzymes in cytoplasm) Single stranded and every 3 bases code for an amino acid (codons)

Question 30

What is tRNA?

Answer 30

Found in cytoplasm Single stranded but folded to create clover leaf shape held in place by hydrogen bonds Brings specific amino acids to ribosomes Determined by the 3 bases found on the tRNA (anticodon) which are complimentary to 3 bases on the mRNA (codon)

Question 31

Why is DNA replication described as semi-conservative?

Answer 31

One strand is conserved and a new strand is created

Question 32

When in the cell cycle does DNA replication occur?

Answer 32

S-phase in interphase

Question 33

What are the stages of DNA replication?

Answer 33

1. DNA helicase beaks the hydrogen bonds between the complimentary bases to unwind the double helix and the strands separate 2. Both strands act as templates for DNA replication 3. Free-floating DNA nucleotides align opposite their complementary base on the template stand of DNA. Hydrogen bonds form between base pairs 4. DNA polymerase joins adjacent DNA nucleotides together, forming a phosphodiester bond between these nucleotides to create a new polymer chain of DNA

Question 34

What are the main features of the genetic code?

Answer 34

Degenerate Universal Non-overlapping

Question 35

What is meant by degenerate in the genetic code?

Answer 35

Amino acids are coded for by more than one triplet of bases

Question 36

What is meant by universal in the genetic code?

Answer 36

The same triplet of bases codes for the same amino acid in all organisms

Question 37

What is meant by non-overlapping in the genetic code?

Answer 37

Each base in a gene is only part of one triplet of bases that codes for one amino acid. Each codon, or triplet of bases, is read as a discrete unit.

Question 38

What are the two stages of protein synthesis?

Answer 38

Transcription - where the DNA sequence for one gene is copied into mRNA Translation - where the mRNA joins with a ribosome and a corresponding tRNA molecule brings the specific amino acid the codon codes for

Question 39

What are introns?

Answer 39

Sequences of bases in a gene that do not code for amino acids and therefore polypeptide chains. These get removed, spliced, out of mRNA molecules after transcription

Question 40

What are exons?

Answer 40

Sequences of bases in a gene that code for a sequence of amino acids

Question 41

What is a start codon?

Answer 41

At the start of every gene Allows ribosomes to attach Initiates translation

Question 42

What is a stop codon?

Answer 42

At the end of every gene 3 bases that do not code for an amino acid Causes ribosome to detach and ends translation

Question 43

What is the process of transcription?

Answer 43

DNA helicase breaks down hydrogen bonds between bases in the two strands of DNA DNA helix unwinds - one strand acts as a template Free mRNA nucleotides align opposite exposed complementary DNA bases RNA polymerase joins together the adjacent RNA nucleotides, forming phosphodiester bonds - creates new mRNA polymer chain Once gene is copied, mRNA is modified and leaves the nucleus through the pores

Question 44

What is the process of translation?

Answer 44

mRNA attaches to the small subunit of the ribosome at the start codon tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA (two tRNA molecules can fit in at once) Two amino acids get delivered by the tRNA molecule, which join together via peptide bonds which is catalysed by an enzyme using ATP Ribosome moves along the mRNA molecule to the next codon and another complementary tRNA will attach to the next codon on the mRNA Ribosome continues until the stop codon so the ribosome detaches A polypeptide chain is now formed and will enter Golgi body for folding and modification