Chapter 8 – The Cell CycleWhat molecule stores your genetic information or determines everything about you?

DNA – a nucleic acid

How are DNA molecules arranged in the nucleus?

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell CycleAs you can see DNA is:

1. Arranged in a double helix conformation

2. The double helix is wound around histone proteins which serve to compact the DNA tightly – the resulting structures are called nucleosomes

3. The nucleosomes are coiled into even tighter packages

4. The resulting chromatin is a tangled mass of thin threads of DNA

5. During the process of cell division chromatin condenses into highly compacted structures called chromosomes which are visible under light microscopy

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell CycleWhat does a cell have to do to reproduce?

The Cell Cycle

Phases include:

1. Interphase – Preparation phases for mitosis

2. Mitosis – Cell division or splitting

How do you think the cell has to prepare for the division or splitting step?

Interphase

1. G1 (Growth)

2. S

3. G2 (Growth)

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell CycleInterphase (G1)

Growth & preparation of the cell for division, including an increase in size & the number of organelles

During G1 an enzyme called S-kinase combines with a protein called S-cyclin.

This interaction activates the S-kinase which will phosphorylate (Do you remember what this means?) a protein that will initiate the S phase of interphase

Interphase (S)

Synthesis or doubling of the DNA

Each chromosome is duplicated & the resulting sister chromatids are joined at a pinched region called the centromere

Interphase (G2)

Continued growth & preparation for mitosis

During G2, a second enzyme called M-kinase combines with M-cyclin

This interaction phosphorylates a protein that will initiate mitosis

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell CycleMitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

5. Cytokinesis

Prophase

Centrosomes, composed of centrioles & microtubules, migrate toward opposite ends of the cell

The nuclear envelope & nucleolus begin to & will disappear by the end of prophase

The chromosomes condense & are visible

Spindle fibers (microtubules) will form & specialized ones called kinetochore fiberswill attach to the centromeres of the duplicated chromosomes

Chromosomes are not arranged in any specific orientation

Chapter 8 – The Cell CycleMetaphase

The kinetochore fibers push & arranged the duplicated chromosomes along the equator of the cell (metaphase plate)

Anaphase

The sister chromatids are separated from one another forming two daughter chromosomes that move toward the opposite poles of the spindle

The chromatids ride the fibers toward the poles like a train on a railroad track

Telophase

Reverse prophase

Spindle fibers disappear

Nuclear envelope & nucleolus reappear

Chromosomes de-condense back into chromatin

Chapter 8 – The Cell CycleCytokinesis – cytoplasmic cleavage to separate the cell into 2 distinct daughter cells

Animal cells

Begins in late anaphase with the initiation of a cleavage furrow, which is an indentation of the cell membrane

It develops due to the constricting action of a band of actin filaments called the contractile ring

The ring continues to “pinch off” the cell until it is separated into 2 daughter cells

Plant cells

The cell wall prevents this “pinching” effect as seen in animal cells

Instead the Golgi apparatus produces vesicles which move along the microtubules to the mid-point of the cell

These vesicles will fuse forming the cell plate, which will eventually form the new cell membrane of the 2 new daughter cells

Cell wall will be formed following cell membrane formation

Chapter 8 – The Cell Cycle

Chapter 8 – The Cell CycleWhy is the diploid # of chromosomes in all stages of mitosis the same rather than being doubled due to the S phase of interphase? Or

How do you count chromosomes?

You count chromosomes by their centromeres

Since the duplicated chromosomes are called sister chromatids connected by their centromeres, the total is 4 based on the # of centromeres, even though you see a total of 8 sister chromatids in the previous figure

Chapter 8 – The Cell CycleCell division in prokaryotic cells

What do you think a prokaryotic cell has to due to reproduce?

Does it have as many “moving parts” as a eukaryotic cell?

Binary fission

Since the prokaryotic cell does not have to worry about a nuclear envelope or membrane bound organelles, reproduction in these cells are simpler.

Basically, the single loop of DNA is replicated & each copy is attached to the cell membrane at the membrane fold where binary fission begins

As the cell pinches in two, the DNA molecules are pulled apart by the moving cell membrane

Chapter 8 – The Cell CyclePRACTICE QUESTIONS

1. What is a nucleosome?

2. How does chromatin differ from chromosomes?

3. What is a karyotype?

4. What are the phases of the cell cycle?

5. What are the phases of interphase? What happens during each phase?

6. What are the phases of mitosis? What happens during each phase?

7. What does a kinase do?

8. How do animal & plant cell telophase differ from one another?

9. What is binary fission?