Developmental Biology Lecture - Cell Cycle, Mitosis and Meiosis

Cell Cycle

It is a series of events that takes place in a cell as it grows, replicate their DNA and divides

Cell Cycle

It is vital process for growth, development, repair and maintenance of organisms

Cell Cycle

It is highly variable

Cell Cycle

It is monitored by internal controls or checkpoints

Interphase

The cell grows and copies its DNA

G1

Cell growth

S phase

DNA synthesis

G2

More growth, preparation for mitosis

Mitosis

The cell divides its DNA and cytoplasm, forming two new cells

Mitosis

Prophase

Metaphase

Anaphase

Telophase

G0

Resting state where the cell performs its functions and is not preparing to divide

Interphase

the time between cell divisions

Interphase

DNA is found as thin threads of chromatin in the nucleus

G1

Growth I phase

G1

prepares for cell division

G1

cell continually imbibes water/nutrients and grow

S phase

Synthesis phase

S phase

DNA replication and chromosome duplication

G2

Growth II phase

G2

RNA and protein synthesis

G2

Centriole synthesis and other raw materials needed for cell division

Mitosis

produces new cells for growth and tissue repair and replacement

Mitosis

nuclear division plus cytokinesis

Mitosis

produces two identical daughter cells, during prophase, prometaphase, metaphase, anaphase, and telophase

Prophase

the chromatin condenses into chromosomes

Prophase

the centrioles move to the opposite ends of the cell

Prophase

the nucleolus and the nuclear envelope disappear

Prophase

Microtubules form near the centrioles and project in all directions

Prophase

spindle fibers, project toward an invisible line called the equator and overlap with fibers from opposite centrioles

Metaphase

the chromosomes align in the center of the cell in association with the spindle fibers

Metaphase

some spindle fibers are attached to kinetochores in the centromere of each chromosome

Anaphase

the chromatids separate, each chromatid is then referred to as a chromosome

Anaphase

the chromosome number is doubled, and there are two identical sets of chromosomes

Anaphase

the chromosomes, assisted by the spindle fibers, move toward the centrioles at each end of the cell

Anaphase

Separation of the chromatids signals the beginning of anaphase, and, by this phase ended, the chromosomes have reached the poles

Telophase

migration of each set of chromosomes is complete

Telophase

The chromosomes unravel to become less distinct chromatin threads

Telophase

The nuclear envelope forms from the endoplasmic reticulum

Endoplasmic reticulum

here is where the nuclear envelope forms from

Telophase

The nucleoli form

Cytokinesis

cytoplasmic division

Cytokinesis

continues to form two cells

Cell Cycle Regulation and Checkpoints

Checkpoints are mechanisms that regulate the eukaryotic cell cycle, ensuring DNA integrity and proper chromosome segregation

G1 checkpoint (Restriction point)

G2 / M checkpoint

M checkpoint (Spindle checkpoints)

3 major checkpoints

Restriction point

other term for G1 check point

G1 checkpoint

near the end of G1

G2 / M checkpoint

checkpoint before mitosis

Spindle checkpoint

other term for M checkpoint

M phase

checkpoint during metaphase

1. Cell Growth Checkpoint

2. DNA Synthesis Checkpoint

3. Mitosis Checkpoint

The Cell Cycle and the Checkpoints

Cell Growth Checkpoint

Checkpoint that occurs toward the end of growth phase 1 (G1)

Cell Growth Checkpoint

Checks whether the cell is big enough and has made the proper proteins for the synthesis phase

G0

This is the resting period until the cell is ready to divide

DNA Synthesis Checkpoint

Checkpoint that occurs during the synthesis phase (S)

DNA Synthesis Checkpoint

Checks whether DNA has been replicated correctly

Mitosis

The cell goes here after DNA Synthesis Checkpoint

Mitosis Checkpoint

Checkpoint that occurs during the mitosis phase (M)

Mitosis Checkpoint

Checks whether mitosis is complete

Mitosis Checkpoint

This checkpoint is where the formation of 2 daughter cells occur

Restriction

Other term for G1 checkpoint

Regulator molecules of cell cycle

Either promote progress of the cycle to the next phase (positive regulation or halt the cycle (negative regulation)

Regulator molecules of cell cycle

May act individually, or can influence the activity or function of other regulatory proteins

Cyclins and Cyclin-dependent kinases (CDKs)

Positive regulators

Positive regulators

Activate other proteins that help the cycle to move forward through various checkpoints

Cyclins

These are active only when they are tightly bound to CDKs and will phosphorylate and activate other proteins

Positive regulators

Triggered external and internal signals

Retinoblastoma protein (Rb), p53 and p21

Negative regulatory molecules

Negative regulatory molecules

Active molecules that halt the cell cycle

Negative regulatory molecules

Main cause of unchecked progress through cell cycle was a faulty copy of these regulatory proteins

tumor suppressors

other term for negative regulatory molecules

Negative regulatory proteins

Act at the G1 checkpoint (adequate energy reserves, large enough and damage to DNA)

p53

detects DNA damage and recruit enzymes to repair, if not can trigger apoptosis

p51

is produced in response to p53 and stops cycle by inhibiting CDK/cyclins

Rb

blocks production of proteins necessary for cell cycle to proceed

Mitosis

Division of Somatic or Body cells

Meiosis

Division of Gametic or Sex cells

Mitosis

There is no genetic variation in this cell division

Meiosis

Genetic variation is present (with exchange of genes during synapsis)

Mitosis

Products are 2 diploid (2n) daughter cells

Meiosis

products are 4 haploid (n) daughter cells

Mitosis

Cell division with a single stage - part of cell cycle

Meiosis

Cell division terminal with 2 stages: Meiosis I and II

Meiosis

Two successive nuclear divisions occur, Meiosis I (Reduction) and Meiosis II (Division)

Reduction

Other term for Meiosis I

Division

Other term for Meiosis II

4 haploid cells

Meiosis produces how many haploid cells

Reduction/division

old name for meiosis

Meiosis I

reduces the ploidy level from 2n to n (reduction)

Meiosis II

divides the remaining set of chromosomes in a mitosis-like process (division)

Meiosis I

Most of the differrences between processes in meiosis occur here

Reductional Division

Meiosis I or?

Prophase I

chromosomes pair up

Metaphase I

Alignment of bivalents at the equatorial plane

Anaphase I

Separation of bivalents to form 2 univalents

Telophase I

Formation of 2 haploid daughter cells

Equational Division

Meiosis II or?

Meiosis II

stages similar to mitosis

Prophase II

univalents contract

Metaphase II

alignment of univalents at the equatorial plane

Anaphase II

separation of univalents into 2 sister chromatids and migration to the opposite poles