Name______Per_____

PAP Biology Chromosomes & the Cell Cycle- Notes

Chromosome Overview

A chromosome is a coiled molecule of DNA that contains many genes.

A gene is a segment of DNA that determines an organism’s traits.

Since chromosomes contain DNA, where do you think you would find chromosomes inside of the cell? ______

Structure of a Chromosome:

•chromatin- thin strands of DNA & protein found in the nucleus

–copied before cell division

–chromatin is “thin and thread-like”

•chromatid- one of 2 exact copies of DNA that make up a chromosome

•chromosome- coiled up chromatin

•centromere- where the two chromatids attach (it holds them together)

Chromosomal Hierarchy

Draw and Label:

DNA

Other Information:

•chromosomes are found in your somatic cells

•somatic cells are “body cells” that make up your liver, heart, skin, hair, etc etc

–ALL of your cells EXCEPT for sperm or eggs

•humans have 23 pairs of chromosomes in every somatic (body) cell

–this is equal to 46 chromosomes total in every somatic cell

–you receive one of each pair from your mom and one of each pair from your dad

Cell Basics

•There are trillions of cells in your body.

•Cells are microscopic

•Cells have DNA inside a structure called the nucleus

•The nucleus is “surrounded” by a structure called the nuclear envelope

•Cells are filled with a jelly like substance called the cytoplasm

Cell Division

•Cell division is the splitting of a single cell into two daughter cells

–Mitosis – Process of nuclear division (dividing the nucleus)

–Cytokinesis - Process of division of the cytoplasm

Cells divide because the organism needs to:

–Grow- our cells don’t get bigger in size, they get bigger in number

–Repair- needed because of worn out or injured cells (your skin cells are replaced every 28 days; your stomach every 7)

–Reproduce:

•Asexual – one parent. Offspring identical to parent – mitosis or binary fission

•Sexual – combination of genetic material from two parents – meiosis (more on this later!)

Asexual reproduction:

Binary fissionMitosis

The Cell Cycle

•Occurs in somatic cells

•What are somatic cells? ______

•a set of events that results in two new daughter cells, which then start the process again.

–Interphase

•G1  S  G2

–Prophase

-- Metaphase

–Anaphase

–Telophase

Cytokinesis

Interphase

–90% of the time, the cell is in this phase

–The cell grows

–Performs operations unique to the type of cell (stomach cells make digestive enzymes, some white blood cells make antibodies, etc)

Three stages of Interphase:

-G1 (growth stage 1)

-S (synthesis)

G2 (growth stage 2)

GROWTH 1 STAGE – G1

•Decides whether or not the cell will divide

•Makes its structural proteins and enzymes to perform its functions

–A pancreas cell will produce and secrete insulin

–Salivary gland will produce and secrete enzymes in the mouth to aid in digestion

S Synthesis (DNA Replication)

–Each of the chromosomes is copied

GROWTH 2 PHASE – G2

–DNA replication is checked by DNA repair enzymes

–Cell prepare for mitosis

–Proteins organize themselves to form a series of fibers called the spindle

Interphase in an animal cell Interphase in a plant cell

Note that the DNA is in the form of chromatin- loose and in long strands. The nucleolus (the dark circle inside the nucleus) is usually visible during interphase but not during mitosis

Mitosis

Follows interphase when the cell is ready to divide

•4 main parts

–prophase, metaphase, anaphase, telophase

–P-MAT

PROPHASE

  • Condensing of 2 chromatids
  • Chromatin coils up
  • Chromosomes become visible
  • Centrioles replicate and begin to move to opposite sides of the cell
  • Nuclear envelope (the outside part of the nucleus) disappears
  • Notice in the picture that the chromatin begins to coil up and you see “space” in the nucleus between what will soon be evident as separate chromosomes

METAPHASE

  • Spindle fibers move the chromosomes to the middle
  • This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome
  • Chromosomes in metaphase have their centromeres lined up in the middle and their long arms are trailing from each side. Some students think it looks like Chinese characters, others have compared it to stitches on a zombie mouth.

ANAPHASE

  • Each chromosome is attached to a spindle which moves it toward one pole
  • Chromatids move apart from one another
  • Results in equal separation and distribution of chromosomes
  • In anaphase the centromeres are in rows at each end of the cell and the arms of the chromosomes are trailing away toward the middle of the cell. Some students think this looks like a scary zombie mouth opening

TELOPHASE

  • Newly separated chromatids arrive at opposite ends of cell
  • nuclear envelope reappears around the daughter nuclei.
  • The chromosomes uncoil and are no longer visible
  • Cytokinesis may also begin during this stage.
  • This phase is opposite of prophase in the events that happen
  • End with two new nuclei (one for each new cell)
  • In telophase the 2 new cells are preparing to enter interphase. The chromosomes uncoil. In this picture you can see the cell wall forming between the two “wads” of chromatin. This is called a cell plate until it reaches both sides of the old cell and divides it into 2 new cells

CYTOKENISIS

•Process in which the cytoplasm divides and two separate cells (daughter cells) form.

•In animals, it begins with the formation of a cleavage furrow

•In plants, a new cell plate forms, then cell wall forms

What differences do you see between animal cell division and plant cell division?

(Hint: does one type of cell have something the other doesn’t?)

1.______

______

______

2. ______

______

______

3.______

______

______

Can you identify the phase each cell is in?

MITOSIS—Summary

Prophase- chromosomes visible (P for Phat), nuclear membrane disappearing chromosomes condense/fatten and become visible)

Metaphase- sister chromatids lined up in the middle/equator (M for middle, chromosomes lined up in the middle of cell)

Anaphase- sister chromatids pulled apart (A for Apart or Away because the chromatids pull apart and move away from center)

Telophase- chromosomes are at ends of cell, cells prepare to separate (T for Two new nuclear envelopes are forming)

Not all cells reproduce

•some leave the cell cycle here and do not undergo cell division

–red blood cells – which “kick out” their nucleus to make room for the hemoglobin and therefore can’t divide

–brain and spinal cord cells – rarely if ever divide; called G0 (pronounced G naught)

•G0

–pronounced G “not”

–there are some cells, like nerves cells, that do not divide

–those cells stay in the G0 phase

–for example, nerve cells typically do not undergo mitosis meaning your body cannot make more nerve cells

•this is why if nerve damage is usually permanent

Other cells can’t stop reproducing

Abnormal Cell Cycle: Cancer

What causes cancer?

•Cancer is caused by mutations (changes) in the DNA, including the genes that regulate the cell cycle

•Basically:

–uncontrolled cell growth

•cancer cells grow and divide as long as they receive nutrients

•cancer cells crowd normal cells causing tissues and organs to stop working

Environmental factors can increase the risk of cancer.

•Substances that are known to cause cancer are called carcinogens(kar SIH nuh junz).

•Tobacco, tobacco smoke, and alcohol, are examples of carcinogens

•Some viruses are linked to cancer

•HPV (human papilloma virus) can lead to cervical cancer as well as other forms of cancer

•Mutagens cause mutations, which can lead to cancer.

•Radiation (x-rays, UV light) is a mutagen. So are some chemicals.

Websites

•Cell Mitosis Lab Practice

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•Mitosis pictures & Video

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•Cell Cycle Interactive Game

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