Cell Cycle Notes/Karyotype/Cancer

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Basic Info

Levels of Organization

cell --> tissue --> organs --> organ system --> organism

Why Do Cells Reproduction

Increase cell size

Cell maintenance

Make new cells

Repair and replace

Parent vs Daughter Cells

Parent Cell

original cell

divides to make two daughter cells

Daughter Cell

new cells formed from original

genetically identical to the parent cell

Checkpoints

Checkpoints exist to prevent mutations in the DNA.

1. End of G1 - will check for proper cell growth

Checks for:

Nutrients

Growth Factors

DNA Damage

2. End of G2 - checks for DNA malfunctions and proper cell size

Checks for:

Cell Size

DNA Replication

3. Middle of Mitosis

Checks for:

Chromosome Spindle Attachment

Internal vs External Factors

External Signals: if the cell starts touching other cells, the cell cycle is turned off

Internal Signals: different types of growth hormones and proteins turn the cell cycle on or off

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Cell Cycle

a continuous process where cells grow, make copies of chromosomes, and divide to make daughter cells

Consists of three major phases

1. Interphase

Interphase is the period of growth and DNA replication that occurs between cell divisions. This process consists of three phases.

1. Gap 1 (G1)

The period of cell growth before DNA is duplicated. This period takes place in the daughter phase.

2. Synthase Phase (S)

The period when DNA or chromosomes are being duplicated.

3. Gap 2 (G2)

The period after DNA is duplicated and prepares for cell division.

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2. Mitosis

Mitosis: division of the nucleus

Chromatin

DNA is unraveled (string-like)

Sister Chromatid

A single chromosome

Homologous Chromosome

2 chromatids connected from each parent

Homologous Pairs

2 of the same homologous chromosome

Phases of Mitosis

Prophase

Chromatin condenses into chromosomes

Centrioles separate

Spindle fibers form

Nucleus breaks down

Metaphase

Chromosomes line up in the center of the cell

Spindle fibers connect to chromosomes

Anaphase

Chromosomes separate at the centromere and sister chromatids move away from each other

Chromosomes pulled towards opposite poles of the cell by spindle fibers

Telophase

Chromosomes unravel into thin strands of DNA (chromatin)

Spindle fibers disappear

Nucleus membrane reappears as nuclei are formed

Results in two identical cells

Cytokinesis

The actual division of the cytoplasm

Different in plant and animal cells

Animal cells - pinches the cells apart

Plant cells - a cell plate is formed, this becomes the new cell wall

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3. Meiosis

Meisosis: cell divison to make gametes

Haploid: cell has half the number of chromosomes (n)

In humans, the haploid amount is 23 (n)

Diploid: cell has a full set of chromosomes (2n)

In humans, the diploid amount is 46 (2n)

Meiosis 1

Interphase 1

DNA is in chromatin form

During the S phase, DNA replicates

Cells grow in prep for the division

Prophase 1

Chromatin condenses into a homologous chromosome

Nucleus disappears

Spindle fibers form

Tetrad occurs

Crossing over occurs: exchange of genetic material between a homologous pair

Metaphase 1

Tetrads (homologous pairs) line up in the middle of the cell

Anaphase 1

Tetrads separate and each homologous chromosome moves to opposite ends of the cell

Telophase 1

Nucleus appears

Spindle fibers disappear

Cytokinesis 1

Cytoplasm divides into 2 cells

2 haploid daughter cells

Meiosis 2

Interkinesis

Resting phase

No DNA replication

Prophase 2

Chromosomes form again in both cells

Nucleus disappears

Spindle fibers form

Crossing over does not occur

Metaphase 2

Homologous chromosomes line up in the middle of the cell

Anaphase 2

Chromosomes pull apart at the centromere

Sister chromatids move to opposite ends of the cell

Telophase 2

Nucleus reappears

Spindle fibers disappear

Chromosomes unravel

Cytokinesis 2

Cells divide into 4 cells

All cells are now haploid gametes (sex cells)

All cells are genetically different

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Karyotype

A karyotype is a picture of all chromosomes in an organism. It is used to help identify genetic disease due to abnormal numbers or damaged chromosomes.

Nondisjunction: results in too few or too many chromosomes in a cell

Can lead to:

Monosomy: having only 1 chromosome instead of 2

Trisomy: having 3 chromosomes instead of 2

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Cancer

Cancer is an error in the DNA replication process that can alter genes that regulate cell growth.

Cancer: cells that do not “listen” to checkpoints and signal from the body to stop dividing (continuous uncontrolled cell division)

Cancer is caused by mutations and carcinogens, which are environmental factors that cause mutations in DNA.