Bio 1 Topic 7.1 - Cell Cycle And Cell Division.pdf 335g29

Answer the following review questions 1.

How does one cell reproduce itself?

2.

How many pairs of chromosomes are found in a) a sperm cell? b) a muscle cell?

3.

Give 2 examples of sex cells. Which is smaller of the two?

4.

What is the name of the process which produces gametes?

5.

What is the name of the process that produces cells with halF the chromosome of a normal body cell?

6.

From which organ of the body are egg cells produced?

7.

Explain why gametes only need 23 chromosomes in their nucleus.

Topic #7.1: July 24-27, 2018

THE CELL CYCLE Cell Cycle & Cell Division Checkpoints

Overview: The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter The continuity of life is based on the reproduction of cells, or cell division

Overview: The Key Roles of Cell Division In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for Development from a fertilized cell Growth Repair Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division

Figure 12.2

100 µm

(a) Reproduction

200 µm (b) Growth and development

20 µm

(c) Tissue renewal

Most cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information, DNA The exception is meiosis, a special type of division that can produce sperm and egg cells

Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes

Cellular Organization of the Genetic Material Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (non-reproductive cells) have two sets of chromosomes Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells

Distribution of Chromosomes During Eukaryotic Cell Division In preparation for cell division, DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids (ed copies of the original chromosome), which separate during cell division The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached

Figure 12.4

Sister chromatids

Centromere

0.5 µm

Distribution of Chromosomes During Eukaryotic Cell Division

During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei Once separate, the chromatids are called chromosomes

Figure 12.5-3

Chromosomes 1

Chromosomal DNA molecules

Centromere

Chromosome arm Chromosome duplication (including DNA replication) and condensation 2

Sister chromatids Separation of sister chromatids into two chromosomes 3

The Phases of the Cell Cycle I. Interphase: no cell division occurs 1. G1 - growth 1: the cell creates organelles and begins metabolism* 2. S - synthesis: DNA replication happens, chromosomes are copied 3. G2 - growth 2: cell grows in preparation for cell division II. M - Mitotic phase / Mitosis *G0: cells are alive and metabolically active, but do not divide (e.g. heart muscle, eyes, and brain)

The Cell Cycle Control System The Cell Cycle control system is driven by built-in clock that can be adjusted by external stimuli (i.e., chemical messages) Checkpoint - a critical point in the Cell Cycle where ‘stop’ and ‘go-ahead’ signals can regulate the cell cycle

Figure 12.15

G1 checkpoint

Control system

G1

M

G2

M checkpoint G2 checkpoint

S

The G1 Checkpoint - the Restriction Point For many cells, the G1 checkpoint seems to be the most important The G1 checkpoint ensures that the cell is large enough to divide and that enough nutrients are available to the resulting daughter cells

The G1 Checkpoint - the Restriction Point If a cell receives a ‘go-ahead’ signal at the G1 checkpoint, it will usually continue with the Cell Cycle If the cell does not receive the ‘goahead’ signal, it will exit the cycle, switching into a nondividing state called the G0 phase

Figure 12.16

G0 G1 checkpoint

G1 (a) Cell receives a go-ahead signal.

G1 (b) Cell does not receive a go-ahead signal.

The G2 Checkpoint

Ensures that DNA replication in S phase has been successfully completed

The Metaphase Checkpoint

Ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore

The Cycle Clock. Cyclins and Cyclin-Dependent Kinases Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (CDKs) CDKs activity fluctuates during the cell cycle because it is controlled by cyclins, so named because their concentrations vary with the cell cycle MPF (maturation-promoting factor) is a cyclinCDK complex that triggers a cell’s age past the G2 checkpoint into the M phase

Cyclin-Dependent Kinases (CdK’s) Kinases - a protein which activates or deactivates another protein by phosphorylating them Kinases give the go-ahead signals at G1 and G2 checkpoints The kinases that drive these checkpoints must themselves be activated

Cyclins - Activators of Kinases Cyclin - the activating molecule for kinases A protein that derives its name from its cyclically fluctuating concentration in the cell Cyclins accumulate during the G1, S, and G2 phases of the Cell Cycle

Figure 12.17

M

G1

S G2

M

G1 S

G2

M

G1

MPF activity Cyclin concentration

G

S

1

Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

Cdk

Cyclin is degraded

2

M

G

Degraded cyclin

G2 Cdk checkpoint MPF

Cyclin

(b) Molecular mechanisms that help regulate the cell cycle

Maturation-Promoting Factors (MPF’s) MPF complexes - aggregations of CDK and cyclin which initiate mitosis

Formed by the G2 checkpoint when enough cyclin is available MPF functions by phosphorylating key proteins in the mitotic sequence

Maturation-Promoting Factors (MPF’s) Later in mitosis, MPF switches itself off by initiating a process which leads to the destruction of cyclin. CDK, the non cyclin part of MPF, persists as an inactive form until it associates with new cyclin molecules synthesized during the interphase of the next round of the Cell Cycle

Figure 12.17

M

G1

S G2

M

G1 S

G2

M

G1

MPF activity Cyclin concentration

G

S

1

Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

Cdk

Cyclin is degraded

2

M

G

Degraded cyclin

G2 Cdk checkpoint MPF

Cyclin

(b) Molecular mechanisms that help regulate the cell cycle

Figure 12.19

Anchorage dependence

Density-dependent inhibition

Density-dependent inhibition

20 µm

20 µm (a) Normal mammalian cells

(b) Cancer cells

Figure 12.18

Scalpels

1 A sample of human connective tissue is cut up into small pieces.

2 Enzymes digest the extracellular matrix, resulting in a suspension of free fibroblasts.

Petri dish

3 Cells are transferred to culture vessels.

Without PDGF

4 PDGF is added to half the vessels.

With PDGF

PDGF: platelet-derived growth factor

10 µm

Loss of Cell Cycle Controls in Cancer Cancer cells do not respond normally to the body’s control mechanisms Cancer cells may not need growth factors to grow and divide They may make their own growth factor They may convey a growth factor’s signal without the presence of the growth factor They may have an abnormal cell cycle control system

Loss of Cell Cyle Controls in Cancer Cells A normal cell is converted to a cancerous cell by a process called transformation Cancer cells that are not eliminated by the immune system form tumors, masses of abnormal cells within otherwise normal tissue If abnormal cells remain only at the original site, the lump is called a benign tumor Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors