Download DNA Replication - Bi-YOLO-gy

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DNA Replication
DNA replication is the process by which DNA makes a copy of itself during cell division.
Steps of Replication:
1.
The first step in DNA replication is to ‘unzip’ the double helix DNA molecule. This is carried out by an enzyme called
helicase which breaks the hydrogen bonds holding the complementary bases of DNA together (A with T, C with G).
2. The separation of the two single strands of DNA creates a ‘Y’ shape called a replication fork. The two separated
strands will act as templates for making the new strands of DNA.
3. One of the strands is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strand. The
other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand. As a
result of their different orientations, the two strands are replicated differently:
Leading Strand:
A short piece of RNA called a primer comes along and binds to the end of the leading strand. The primer acts as
the starting point for DNA synthesis. The enzyme DNA polymerase binds to the leading strand and then ‘walks’ along it,
adding new complementary nucleotide bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction. This sort of
replication is called continuous.
Lagging strand:
Numerous RNA primers bind at various points along the lagging strand. Chunks of DNA, called Okazaki
fragments, are then added to the lagging strand also in the 5’ to 3’ direction. This type of replication is called
discontinuous as the Okazaki fragments will need to be joined up later.
4. Once all of the bases are matched up (A with T, C with G), an enzyme called exonuclease strips away the primer(s).
The gaps where the primer(s) were are then filled by yet more complementary nucleotides.
5. The new strand is proofread to make sure there are no mistakes in the new DNA sequence.
6. Finally, an enzyme called DNA ligase seals up the sequence of DNA into two continuous double strands. The result
of DNA replication is two DNA molecules consisting of one new and one old chain of nucleotides. This is why DNA
replication is described as semi-conservative, half of the chain is part of the original DNA molecule (parent/template
strand), half is newly synthesized (daughter strand).
7. Following replication the new DNA automatically winds up into a double helix.
DNA Replication Drawing
Directions:
Using pencil, you will draw a representation of DNA replication along the leading and lagging strands. Follow the directions
below, drawing each element in its proper location along the replicating DNA strand. Once you are sure everything is in the
correct place, complete your drawing by adding color to distinguish objects as separate.
1. On the diagram below, label the replication fork
3. Create a symbol for and label helicase
4. Create and label the leading strand (with complementary bases attached)
5. Create and label a DNA polymerase on the leading strand
6. Create and label an RNA primer on the leading strand
7. On the lagging strand, draw and label at least two Okazaki fragments (with complementary bases attached)
8. Create and label an RNA primer on the lagging strand
9. On the lagging strand, draw and label at least one DNA ligase
3’
5’
3’
Key:
Helicase:
DNA polymerase:
5’
RNA primer:
DNA ligase:
DNA Replication Analysis Questions:
1. Why would DNA need to make a copy of itself?
2. What type of bonds hold bases together in a DNA molecule?
3. What is the role of the Helicase?
4. What is the role of the RNA primers?
5. What is the role of DNA Polymerase?
6. What is the role of the Ligase?
7. What enzyme strips away the RNA primers? Why is this important?
7. Is the leading strand being built toward or away from the replication fork?
8. Is the lagging strand being built toward or away from the replication fork?
9. What does semi-conservative mean? Why do you think the DNA replicates this way?
DNA & RNA REVIEW:
DNA vs. RNA
Location in the cell
Structure
DNA
RNA
1.
What is the RNA base called that starts with a “U”?
2. What are the 3 types of RNA and what are their jobs?
3. What is the function of RNA (what does it assist in doing)?
Base Pairing
Sugar
Protein Synthesis:
4. What are the steps (in order) of protein synthesis?
a.
b.
5. What is the product of transcription? _____________________________________________________
6. Where does transcription take place? ____________________________________
7. How many mRNA strands are produced during transcription? ____________________
8. A group of 3 mRNA bases is called a _______________________.
9. If a DNA strand reads GCATAGATTACA, what is the complimentary strand made during transcription?
10. Where does mRNA travel to at the end of transcription? _______________________________
11. Where does translation occur? ________________________________
12. What does mRNA attach to? _____________________________________________
13. What does tRNA have that allows it to match the mRNA codons? ____________________________________
14. What is the function of tRNA?
15. What is the final product of translation? ________________________________________________________
16. Using the DNA strands below, write the complementary mRNA strands and the amino acid sequence that is
formed using the codon chart above.
DNA
mRNA AA Sequence
DNA
mRNA AA Sequence
DNA
mRNA AA Sequence