4.1.1 DNA Structure and Replication

Question 1

What is DNA and where is it found

Answer 1

• in eukaryotic cells= Double stranded molecule that occurs bound to proteins (histones) in chromosomes in the nucleus. Also in mitochondira and chloroplasts
• in prokaryotic cells= unbound, circular DNA floating in the cytosol

Question 2

What are the 4 different nitrogen bases in DNA and what are the complementary pairings?

Answer 2

A (acedine) pairs with T (thymine)

C (cytosine) pairs with G (guanine)

Question 3

What is the structure of DNA?

Answer 3

Consists of:

• a chain of nucleotides on each strand
• nucleotides consist of = sugar (5’-3’ ring), phosphate, and nitrogen bases

Question 4

How do nitrogen bases bond together as pairs?

Answer 4

Through hydrogen bonds

*note these are weak so the bonds can be broken by helicase*

Question 5

What are the four stages of DNA replication called?

Answer 5

1. Separation of Strands
2. Initiation
3. Elongation
4. Termination

Question 6

What is the function of DNA?

Answer 6

codes for proteins to control all cell activities, codes for RNA to create genes

Question 7

How do DNA strands separate?

Answer 7

The enzyme helicase unwinds and unzips DNA by breaking the hydrgen bonds between nitrogen bases.

The newly exposed single strands act as a template for new strands

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Question 8

What is the final product of DNA replication

Answer 8

2 identical strands of DNA (each containing one strand from the original strand)

*may be held together by a centromere (protein)

(the lil dot when you draw chromosomes)

Question 9

What happens during the initiation stage of DNA replication?

Answer 9

• replication occurs at many points along a DNA strand called “origins of replication”
• Helicase attaches at these origin points and unzips and unwinds the DNA –> these create replication forks and bubbles
• this happens simultaneously to speed up the process

Question 10

What happens in the elongation stage of DNA replication?

Answer 10

• short strand of RNA, RNA primer, must first bind to starting point of replication before DNA polymerase can add new nucleotides to 3’ end of previous nucleotides
• leading stran forms continuously
• laggin strand recieves many sRNA primer short sections as new DNA is unveiled
• when fragments cover the whole length of lagging strand, RNA primers are removed and replaced by DNA ligase

Question 11

What happens during the termination stage of DNA replication?

Answer 11

DNA replication is terminated when the replication fork is stopped –> when a particular protein binds to the termination sequence site in the DNA

Question 12

What is the purpose of 5’-3’ in DNA structure

Answer 12

The 5’-3’ strands determine which strand will have the leading replication strand and which will have the lagging strands

The strand with the 5’ direction= lagging strands

The strand with the 3’ direction= leading strands