Eukaryotic Cell Cycle

Question 1

What is interphase?

Answer 1

The longest and first stage of the cell cycle. During the time the cell synthesises all needed proteins, DNA, and organelles. Has substages of G1 S and G2.

Question 2

What is the G1 phase?

Answer 2

The cell grows by increasing the volume of the cytosol, synthesises proteins and replicates its organelles.

Question 3

What is the S phase?

Answer 3

The synthesis phase where the cell replicates its DNA turning one chromosome into two sister chromatids.

Question 4

What is the G2 Phase?

Answer 4

Cell continues to grow, by increasing volume of cytosol and continues synthesising protein. All this in preparation for mitosis.

Question 5

Mitosis phases

Answer 5

I - Interphase: The longest and first stage of the cell cycle. During the time the cell synthesises all needed proteins, DNA, and organelles.
P- Prophase: The condensation of chromatin, into distinct chromosomes. Centrioles migrate towards the ends and spindle fibres begin to form.
M- Metaphase: The spindle fibres fully form and attach to the chromosomes and guide them towards the middle of the cell.
A - The spindle fibres split the centromere on the chromosome and pull the chromatids to separate sides of the cell.
T- Telophase: The chromosomes pack together and a new membrane forms producing two identical nuclei. The spindle fibres disintegrate and the chromosomes decondense ( opposite of interphase )

Question 6

What is Cytokenesis?

Answer 6

The cell divides the organelles evenly, and split into two seperate daughter cells. In animals a cleavage furrow pinches the middle of the cell separating it, where in plant cells a cell plate forms turning into the cell wall.

Question 7

DNA Structure

Answer 7

The structure of DNA is a double helix with the 4 bases of Adenine, Thymine, cytosine, guanine. The pairs C-G and T-A. The Helix also has a sugar phosphate backbone.

Question 8

Crucial Enzymes for DNA Replication

Answer 8

Helicase - splits/unzips the DNA by disrupting hydrogen bonds.
DNA Polymerase - Replicates DNA molecules to build a new strand of DNA
Primase - Synthesises small RNA fragments which creates a starting point for Polymerase to begin building new strands.
Exonuclease - Removes RNA primers and replaces with appropriate bases.
Ligase - Joins together DNA fragments

Question 9

What are the Directional Strands

Answer 9

Due to being antiparallel both strands have different directional strands with a 5’ end and a 3’ end. 5’ has a sugar phosphate attached and 3’ has a hydroxyl attached. The leading strand is oreintend in the 3’ to 5’ direction and the lagging strand is in the 5’ to 3’ direction.

Question 10

Steps For DNA Replication

Answer 10

1. DNA strands are unzipped by Helicase which disrupts the hydrogen bonds. SSB proteins keep strands away from each other to avoid reattachment.
2. Primase sets primers on the 3’ ends of the strand setting a starting point of replication.
3. DNA Polymerase beings to build an alternate strand. By binding at the site of the primer and building new complementary base pair always going in a 5’ to 3’ direction. The lagging strand begins building with multiple primers these segments are called okazaki fragments.
4. Once both strands are formed exonuclease removes all RNA primers and replaces them with appropriate bases.
5. Ligase then joins (glues) all the separated okazaki fragments together to create one strand.