unit 1.5 - DNA (replication, nucleotides)

Question 1

Why are strawberries good for extracting DNA?

Answer 1

1. 8 different genomes
2. Pectinase + cellulase enzymes which break down the cell wall for release of DNA

Question 2

What are Nucleotides made up of?

Answer 2

3 main components that combine by condensation reactions
- Phosphate group
- Pentose sugar
- Organic base that contains carbon

Question 3

Describe ATP

Answer 3

A nucleotide
Major energy currency in cells
Energy source in all living organisms/cells

Question 4

What is phosphorylation?

Answer 4

Introducing a phosphate group into a molecule or compound
e.g adding a phosphate group to ADP (adenosine diphosphate)

Question 5

How is ATP formed?

Answer 5

By phosphorylation

Question 6

What is an exergonic reaction?

Answer 6

A reaction that RELEASES energy

Question 7

What is an endergonic reaction?

Answer 7

A reaction where energy is NEEDED (taking in energy)

Question 8

Where in the cell is ATP produced?

Answer 8

Cytoplasm, mitochondria, chloroplasts

Question 9

Name 4 uses of ATP

Answer 9

DNA synthesis from nucleotides
Active transport
Muscle contraction (movement)
Secretion

Question 10

What are the two types of nucleus acids?

Answer 10

Deoxyribonucleic acid - DNA
Ribonucleic acid - RNA

Question 11

What pentose sugar + bases do DNA nucleotides have?

Answer 11

Deoxyribose
Adenine, thymine, cytosine, guanine

Question 12

What pentose sugar + bases do RNA nucleotides have?

Answer 12

Ribose
Adenine, uracil, cytosine, guanine

Question 13

Describe the structure of DNA [4]

Answer 13

• Double stranded polymer of nucleotides (polynucleotide)
• The alternating phosphate groups and pentose sugars form the backbone
• The polynucleotide chains are antiparallel to each other
• Molecule is twisted to form a double helix. This helix is maintained by hydrogen bonding

Question 14

Where is DNA found?

Answer 14

In the nucleus of eukaryotic cells

Question 15

What are the 2 functions of DNA?

Answer 15

Replication and protein synthesis

Question 16

Describe the structure of RNA

Answer 16

• Single stranded polypeptide
• Much shorter than DNA

Question 17

When is DNA copied?

Answer 17

During replication in the interphase

Question 18

How does DNA replication occur?

Answer 18

• Hydrogen bonds holding the base pairs break and 2 halves of the DNA molecule separate
• DNA unwinds
• As DNA strands separate the enzyme DNA polymerase catalyses the free nucleotides to the exposed bases
• This process results in the formation of 2 identical DNA molecules - each made up of one newly synthesized chains and one from the original molecule

Question 19

What is the hypothesis of the Meselson + Stahl experiment?

Answer 19

Semi-conservative
- Each DNA strand acts as a template for new DNA
- Each strand of DNA formed is composed of an original strand and a newly synthesized strand

Question 20

Describe how the Meselson + Stahl experiment works

Answer 20

1. The scientists extracted the bacterial DNA and centrifuged it.
2. The DNA settled at a low point in the tube bc it contained the heavy N^15 isotope.
3. The bacteria were washed, then transferred to a medium containing the normal lighter isotope N^14 and were allowed to replicate once.
4. When extracts of DNA from the first generation culture were centrifuged it was shown to have a mid point density; half the strand was made up of N^15 DNA and the other half was made up of the new N^14 DNA
5. When extracts of DNA were taken from the second generation grown in a N^14 medium, the DNA settled at mid points and high points in the tube after centifugation.
6. This provided evidence which supported the semi conservative hypothesis.

Question 21

Describe transcription

Answer 21

• DNA unwinds and unzips at a particular region to be copied; enzyme helicase catalyses the DNA
• Enzyme RNA polymerase attaches to DNA at the beginning of the sequence to be copied.
• Only one of the DNA stands acts as a template (antisense strand)
• RNA polymerase moves along the DNA forming bonds that add nucleotides one at a time to the RNA
• This results in the synthesis of a molecule of mRNA alongside the unzipped portion of DNA
• Behind the RNA polymerase the DNA stands re join to reform the double helix
• The mRNA carries the DNA code out of the nucleus through a nuclear pore to the cytoplasm and attaches to a ribosome for translation.

Question 22

When does transcription occur?

Answer 22

When the free RNA nucleotides align themselves opposite complimentary nucleotides on the DNA stand

Question 23

Describe translation

Answer 23

• Ribosome acts as framework moving along the mRNA, reading the code.
• mRNA contains triplet codes or codons. Each codon codes for a different amino acid.
• tRNA molecules attach to specific amino acid molecules and carry them to mRNA molecules
• Complimentary anticodon - codon bases align and are held together by the ribosome at an attachment site; a codon - anticodon complex is formed.
• Peptide bonds are formed between adjacent amino acids by condensation reaction.

Question 24

Name 3 variables of the Meselson + Stahl experiment

Answer 24

1. Temperature
2. Time
3. Rate of spin

Question 25

Name 2 enzymes known to be involved in DNA replication and their functions

Answer 25

1. DNA polymerase - joins nucleotides to the ends of the new DNA stand
2. DNA helicase - unwinds DNA and breaks hydrogen bonds between nucleotides