AP Biology Mitosis & Meiosis

When do cells divide?

For growth, replacement of old cells, and for reproduction

• Sometimes we want the same (Mitosis) or different (Meiosis)

How do we get identical daughter cells to form?

The genome must be copied and then each daughter cell gets one of the two copies

• Humans have 46 chromosomes

• Genome = All genes in an organism

• Gene is a section of a chromosome that codes for a protein

Chromosome

Threadlike structures composed of DNA and proteins (Histones)

Replication

Process whereby DNA is identically copied

(Before cell division)

Mitosis

Division of nucleus/genetic information

Cytokinesis

Division of cytoplasm

Chromatin

DNA + Protein (Histones). Thin and fibrous, it will condense into distinct chromosomes during Mitosis/Meiosis

Chromatid

After replication the chromosome consists of 2 sister chromatids joined at the centromere

Bacterial Reproduction

Asexual

Dividing like Mitosis (Clones)

Together this is Binary Fission

Centromere

Specialized region of the chromosome where chromatids are joined. Each chromosome has one centromere

Interphase

Normal section of a cell’s life

• Doing normal cell things

• G1, S, G2

• No chromosomes are visible

Late Interphase

Chromosomes are starting to condense

• Nucleus is beginning to dissolve

Prophase

Nucleus dissolves

Chromatin (DNA + Histones) condense

Spindle fibers form

Prometaphase

Chromosomes begin lining up in the middle of cell

KMT/NKMT begin attaching

Metaphase

Chromosomes line up down middle of cell

KMT attach in centromere region

NKMT attach in cytoplasm

Anaphase

Chromosomes are pulled apart

Chromatids to opposite sides of cell (KMT Pulling)

NKMT push cell into an ellipse

Cytokinesis

Division of the cytoplasm

Meiosis

Produce 4 different cells

Haploid

½ amount of DNA

• These are called gametes

Homologous pair

Chromosome pairs in a cell, one from each parent, carrying the same genes at the same locations but with potentially different versions

Interphase (MEIO)

Nucleus is intact

Chromosomes not visable

Prophase 1

Nucleus is dissolving

• Spindle fibers form

• Homologous chromosomes meet up and crossing over occurs

Metaphase 1

Homologous pairs lineup down center of the cell

• One KMT per chromosome

Anaphase 1

Homologous chromosomes are separated and moved to opposite sides of cell

Telophase 1

Cytokinesis occurs and cell divides

• Nuclear membrane reforms

Prophase 2

Nucleus dissolves

• Spindle fibers form

• Chromosomes condense

NO CROSSING OVER

Metaphase 2

Chromosomes lineup

• Spindle fibers attach

• NKMT attach

Anaphase 2

Sister chromatids are pulled apart

• cells turn into ellipse

Telophase 2

Nuclear membrane reforms

• Chromosomes decondense back into chromatin

• Cytokinesis divides the cells into 4 different cells

Haploid

Single set of unpaired chromosomes (n)

Diploid

Two complete sets of chromosomes, one from each parent (2n)

Checkpoints for the cell cycle

Certain times in the cell cycle, the cell will check to see if everything is okay before moving on

• If it passes G1, the cell divides. If not, it enters G0 phase and doesn’t divide

G0

Normal cell state, Interphase

Cyclin

Protein that controls the timing and progression of the cell cycle by activating CDK’s

CDK

Cyclin Dependent Kinase

• Cyclin binds at allosteric site

• Make more Active CDK by making more Cyclin

MPF

Maturation Promoting Factor

• Checkpoint regulator that ensures a cell is ready for G2 phase

• Must build up enough cyclin to go into mitosis (Body constantly oscillates)

Cancer cells

Uncontrolled cell division

• Does not follow checkpoint

• Normal cells stop dividing when they touch (Cancer cells don’t) Density Inhibition

• Normal cells die when they flake off (Cancer cells don’t) Anchorage Dependency

Cell Communication

How cells talk

• Uses flags and tags (Surface carbs)

• Gets signals from other cells, instruction to start mitosis