2.7/7.1 (DNA Unit)

Question 1

Describe the meaning of “semi-conservative” in relation to DNA replication.

Answer 1

Semi-conservative means the products of DNA replication each contain one of the original DNA strands and one new strand.

Question 2

Explain the role of complementary base pairing in DNA replication.​

Answer 2

Complementary base pairing (A-T, C-G) ensures that the DNA sequence remains consistent after DNA replication. This ensures that the genetic code remains intact between generations.

Question 3

State why DNA strands must be separated prior to replication.

Answer 3

The two strands of the parent DNA molecule must separate so that each can serve as a template for the new DNA strands that are being built.

Question 4

Outline two functions of helicase.

Answer 4

Helicase is an enzyme that attaches to the DNA and moves along the molecule separating unwinding the helix and separating the two strands by breaking hydrogen bonds.

Question 5

State the role of the origin of replication in DNA replication.

Answer 5

The origin of replication is the sequence of DNA nucleotides at which replication is initiated.

Question 6

Contrast the number of origins in prokaryotic cells to the number in eukaryotic cells.​

Answer 6

• Prokaryotic cells have 1 origin of replication (therefor one replication bubble with two replication forks)
• Eukaryotic cells have many origins of replication (therefor multiple replication bubbles that eventually fuse)

Question 7

Describe the movement of DNA polymerase along the DNA template strand.

Answer 7

• DNA polymerase moves along the parent DNA strand from the 3’ end to the 5’ end of the parent strand. The parent/template is read from 3’ to 5’.
• DNA polymerase builds a complementary strand of DNA from the parent/template strand. The daughter strand is built from 5’ to 3’.

Question 8

Describe the action of DNA polymerase III in pairing nucleotides during DNA replication.

Answer 8

• DNA polymerase “reads” a parent/template DNA strand and adds complementary nucleotides to build a new strand of DNA.
• DNA polymerase can only add new nucleotides to the 3’ end of the growing daughter strand.

Question 9

Outline the features of DNA structure that suggested a mechanism for DNA replication.

Answer 9

• Complementary base pairing
  
  • A to T, C to G ensure that genetic message conserved when each strand replicate
• Covalently bonded sugar-phosphate backbone
  
  • relatively strong bonds keep nucleotides in backbone connected in correct sequence
• Hydrogen bonds between complementary strands
  
  • allow complementary strands separate easily for replication

Question 10

Compare replication on the leading strand and the lagging strand of DNA.

Answer 10

• On leading strand, DNA polymerase III move in same direction as helicase, adding complimentary nucleotides to growing daughter strand
• On lagging strand, DNA polymerase III move opposite as helicase

Question 11

Explain why replication is different on the leading and lagging strands of DNA.

Answer 11

Because DNA polymerase III only add new nucleotides to 3’ of growing strand, replication run opposite on leading & lagging strands

Question 12

Outline the formation of Okazaki fragments on the lagging strand.

Answer 12

Because DNA polymerase III moving away from replication fork on lagging strand, must build DNA in short sections called Okazaki fragments

Question 13

Outline the role of the following proteins in DNA replications: helicase, topoisomerase (AKA gyrase), single stranded binding proteins, primase, DNA polymerase III, DNA polymerase I, and DNA ligase.

Answer 13

1. Helicase open DNA helix by breaking hydrogen bonds between nitrogenous bases
2. Topoisomerase (gyrase): hep relieve tension stress on DNA when unwinding
3. Single stranded binding proteins: bind to single stranded DNA, preventing parent strands from reconnecting
4. Primase: synthesize RNA primers needed to start replication
5. DNA polymerase III: main enzyme that build complementary DNA strand by adding nucleotides in 5’ to 3’ direction
6. DNA polymerase I remove RNA primer & replace with DNA nucleotides
7. Ligase covalently bond sugar-phosphate backbone between adjacent okazaki fragments on lagging strand

Question 14

Explain the need for RNA primers in DNA replication.

Answer 14

• Primer is short strand of RNA (=10 bases) tht act as starting point for DNA replication
• Needed because DNA polymerase III can only add nucleotides to existing strand

Question 15

Explain what is meant by DNA replication occurring in a 5’ to 3’ direction.

Answer 15

• 5’ to 3’ has 2 meanings
  
  • new DNA strand built from its 5’ end towards 3’ end
  • new incoming nucleotide triphosphate added from its 5’ end to 3’ end of previously placed nucleotide

Question 16

Define “coding sequences” and “repetitive sequences” of DNA.

Answer 16

• Coding Sequences are the sequences that code for a certain protein that is expressed in the organism.
• Repetitive Sequences (non-protein coding) are the sequences which does not code for a protein but is repeated over and over in the genome, they’re also known as “tandem repeats.”

Question 17

Outline five functions of non-coding DNA sequences found in genomes, one of which must be the telomere.

Answer 17

• satellite DNA: tandemly repeating sequences of DNA; structural component of heterochromatin and centromeres; commonly used for DNA profiling
• telomeres: regions of repetitive DNA at the end of a chromosome; protects against chromosomal deterioration during replication
• introns: non-coding sequences within genes; are removed by RNA splicing prior to the formation of mRNA
• non-coding RNA genes: codes for RNA molecules that are not translated into protein; examples include genes for tRNA
• gene regulatory sequences: sequences that are involved in the process of transcription; includes promoters, enhancers, and silencers

Question 18

Define VNTR.

Answer 18

Variable Number Tandem Repeat (sequences of repeating DNA nucleotides)

Question 19

Explain why VNTR are used in DNA profiling

Answer 19

Each person has a different VNTR, which can be differentiated by the size of the fragments after they are cut by restriction enzymes.

Question 20

Outline the process of DNA sequencing, including the role of chain terminator nucleotides, fluorescence, and electrophoresis.

Answer 20

• Copies of DNA sequences are placed with polymerase, nucleotides, and primers
• Polymerase replicates the sequences and stops when adding dideoxynuceotide
• Strands of new replications of various lengths end with fluorescent nucleotides
• DNA is separated by size in electrophoresis