Progress Check #1: Unit 5 ( Cell Cycle Stages including DNA replication)

Name each phase of the cell cycle

Interphase (G₁, S, G₂) Mitoitic [M] (Mitosis (Prophase, Metaphase, Anaphase, Telophase), Cytokinesis)

G₁ phase

The longest phase (~1/2) where the cell grows, making proteins and lipids and starts synthesizing organelles, preparing for division. It has 1 set of DNA present at the end, and the DNA is chromatins with homologous chromosomes (one from egg, one from sperm).

S phase

DNA replication/Chromosome duplication, (1/3). It ends with 2 sets of DNA and slightly more organelles, with homologous pairs and sister chromatids in the form of chromatin.

G₂ phase

Protein and organelle synthesis (1/6), checks mistakes in DNA replication, ends with 2 sets of DNA and more organelles, with homologous pairs and sister chromatids in the form of chromatin.

Mitosis (4 stages)

Overall this is the nuclear division, ends with 2 sets of DNA and nuclei

Prophase

Nuclear membrane breaks down

Chromatin condenses into chromosomes

Spindle fibers form and attach to chromosomes

Metaphase

Chromosomes line up in the middle of the cell (Metaphase plate)

Anaphase

Sister chromatids are split and move to opposite poles.

Telophase

2 nuclear membranes form

Chromosomes uncoil back into chromatin

Spindle fibers break down

Cytokinesis

Splitting of the cytoplasm. For animal cells, the cleavage furrow forms (contracting ring of microfilaments) like a balloon with a string tied around it to form 2 daughter cells. For plant cells vesicles filled with cellulose form a cell plate, eventually forming a new cell wall, and 2 daughter cells.

G₀

Cells exit the cell cycle pausing division permanently or temporarily occurring after G₁.

DNA replication location

In the S phase, in the nucleus.

Key enzymes for DNA replication

DNA helicase, DNA ligase, DNA polymerase (HeLP the cell with DNA replication).

DNA helicase

Breaks hydrogen bonds of parent molecule, unzipping the DNA strand.

DNA polymerase

Adds matching nucleotides to make the daughter strand. It goes from 5’ to 3’ of the daughter strand (3’ to 5’ of the parent strand for direction) so on one side it creates the leading strand which is continuous with the direction of DNA helicase, and on the other it creates okazaki fragments, constantly adding more DNA polymerase, creating the lagging strand.

DNA ligase

It connects fragments, as DNA replication occurs in bubbles that eventually meet where DNA ligase connects the fragments, including the Okazaki fragments.

Importance of cell division in organisms

1. To maintain a favorable SA:V ratio (stays small) to be able to manage nutrients and waste permanently.

2. With individual cells, the cells differentiate and specialize to perform different cell functions.

3. They can use this to repair as well as grow in size without compromising the SA: V ratio.

4. Unicellular organisms use it to reproduce. Multicellular mostly use it for repairs and growth and sexual (gametes) + asexual reproduction.

Prokaryotes cell division

Binary fission, the cell duplicates the chromosome and seperates the copies, elongating the cell as the copies move to the ‘poles’ eventually dividing into two daughter cells. It is smaller, simpler and has one circular chromosome, and is faster taking only an hour or two to replicate.

Eukaryotes cell division

The cell cycle with its many phases, it is bigger, more complex, 46 chromosome pairs per cell, and it is slower taking at least 24 hours to replicate.

Chromatin

DNA strands wrapped loosely around histomes.

Sister chromatids

Two identical copies of a single replicated chromosome, which join together at the centromere.

Homologous chromosomes

Two chromosomes that resemble eachother in length, centromere position and staining pattern. Tightly coiled, and one comes from egg one comes from sperm.

How does a cell divide in general, how many chromosomes in the daughter cell versus the parent cell.

Prep, division. Same # of chromosomes in parent cell and daughter cell.