Biology Semester 2 Freshman Year - Unit 7: Cell Division

A normal human cell can only divide about…

40-60 times

A normal human cell can only divide about 40-60 times. What happens after this

apoptosis (programmed cell death)

Cells in the body divide at ___ rates.

different

Some cells don’t even divide. True or False

True

What are some examples of cells that constantly divide?

cells that line the gut

What is an example of cells that divide only rarely?

liver cells

What are some examples of cells that do not divide?

neurons and mature red blood cells

Why do cells divide?

1) To increase the Surface Area to Volume ratio - this allows for more efficient material exchange

2) To solve information overload in the cell

3) To replace damaged or dying cells (For example: when you have a cut, your cells are trying to rebuild that tissue)

4) Growth and Development of an Organism

5) Reproduction

If the cell is large, does it have a smaller or larger Surface Area to Volume Ratio?

smaller SA/V Ratio

If the cell is small, does it have a smaller or larger Surface Area to Volume Ratio?

larger SA/V Ratio

Is a larger or smaller Surface Area to Volume ratio better for the cell?

larger

When a cell divides, does its Surface Area to Volume Ratio increase or decrease?

increases (that is one of the reasons why cells divide. The increasing SA/V ratio allows for efficient nutrient exchange because there is more cell membrane available)

What are the two types of cell division?

Mitosis and Meiosis

What is Mitosis and in which organisms does it occur?

• Results in cells that are identical to the original cell.

• Body cells also known as somatic cells use this

• Used for asexual reproduction as well

• happens in eukaryotes

What is meiosis and which organisms does it occur in?

• Results in cells that are genetically different from the original cell

• Used by sex cells also known as gametes

• occur in eukaryotes that sexually reproduce

What is asexual reproduction and which organisms does it occur in?

• Results in producing genetically identical offspring (clones) from a single parent.

• Used by single-celled organisms (prokaryotes) & some

  • Prokaryotes use Binary Fission

    • Pros = rapid population increase.

    • Cons = lack of genetic diversity, which means a decreased chance of survival.

  • Eukaryotes use Mitosis

Sexual Reproduction via Meiosis

• Offspring produced inherit some of their genetic information from each parent

• Occurs in eukaryotes that sexually reproduce

• Formed by the fusion of reproductive cells of each parent (sperm & egg)

  • Pros: Increases genetic diversity, increased chance of survival

  • Cons: Requires more time

Sexual Reproduction =

Meiosis

Asexual Reproduction =

Mitosis

Mitosis occurs in what type of cells??

Somatic cells also known as body cells

Meiosis occurs in what type of cells??

Gametes (sex cells)

What are some limits to cell size?

• The larger a cell becomes, there is…

• Information overload - more demands placed on its DNA

  • (info in DNA is used to build molecules for cell growth)

• Lowering Surface Area to Volume Ratio

  • The surface area is not increasing as fast as the volume increase

    • And less cell membrane available is less efficient for cells to exchange nutrients

    • Also causes a buildup of waste

    • Results in cell division

      • If the cell is not able to divide,

        • Apoptosis will occur

          • Programmed cell death

When cell is large, it has lower or higher Surface Area to Volume Ratio?

lower SA/V Ratio

When cell is small, it is lower or higher Surface Area to Volume Ratio?

higher SA/V Ratio

When a cell divides, does the Surface Area to Volume Ratio increase or decrease as the cell divides?

SA/V Ratio increases

Binary Fission - Asexual or Sexual Reproduction?

Asexual

Prokayotic Chromosomes

• single circular DNA chromosome

• undergo rapid cell division

  • Called binary fission

Eukaryotic Chromosomes

• More DNA than prokaryotes

  • DNA tightly coiled around proteins called histones

    • forms chromatin

    • Chromatin supercoils to form chromosome

Somatic cells? - diploid or haploid

diploid

Somatic cell

every body cell EXCEPT reproductive cells

Another term for sex cells

gametes

Gametes = haploid or diploid?

haploid

Chromosomes in Somatic Cells

• Somatic cells (aka body cells) are any cells of the living organism EXCEPT the reproductive (sex) cells

• Somatic cells are diploid (2n) - two sets of chromosomes

  • Each human somatic cell contains a total of 46 chromosomes (23 from mom, 23 from dad)

    • N= the # of chromosomes in a single set

    • So 2N=46 for humans

Chromosomes in Gametes

• Gametes are another term for sex cells (sperm and egg)

  • Gametes are haploid:

    • Haploid is represented by N, which is a cell with one set of chromosomes.

    • Gametes only contain 23 of the 46 chromosomes, so N=23

If you have a parent cell that contains 22 chromosomes, how many chromosomes would the daughter cells have in mitosis?

22 chromosomes

If you have a parent cell that contains 22 chromosomes, how many chromosomes would the daughter cells have in meiosis?

11 chromosomes

What is the imaging of chromosomes in a cell called?

Karyotype

Eukaryotic Cell Cycle

The cell cycle is composed of interphase (G1, S, and G2, phases), followed by the mitotic phase (mitosis and cytokinesis)

Interphase:

• G stands for Gap, S stands for Synthesis

• G1 Phase: Cell growth, synthesizes proteins

• S Phase: DNA replication - doubles DNA

• G2 Phase: Preparation for division - more growth, organelle production & checks DNA before Mitosis

Mitotic Phase:

• Mitosis occurs - splitting of the nucleus

• Cytokinesis -cytoplasm division that officially splits into two daughter
  cells

In what phase is DNA is in its uncondensed form, chromatin?

Interphase

What is the longest stage of the cell cycle?

Interphase

What happens in the Mitotic Phase?

Genetic information that is contained in the nucleus must be condensed into packages of DNA called chromosomes

Those replicated chromosomes are separated into two new nuclei, so daughter cells are exact copies of the parent cell.

True or False: Interphase includes G1, S, G2 phases

True

What happens in the G1 (Gap 1) phase in the eukaryotic cell cycle?

Cell growth and synthesis of proteins

what happens in the S Phase (Synthesis) in the eukaryotic cell cycle?

DNA gets copied (also known as DNA Synthesis)

What happens in the G2 (Gap 2) phase of the eukaryotic cell cycle?

Prep for division

• more growth

• organelle production

• checks DNA before the Mitotic Phase (PMAT)

What happens in Prophase in Mitosis?

• Genetic material condenses into chromosomes and become visible

• Nucleolus disappears & Nuclear envelope begins to break down

• Spindle fibers form

What happens in Metaphase in Mitosis?

• Centromeres of chromosomes line up on metaphase plate

• Spindles connect centromere of each chromosome to the two poles

What happens in Anaphase in Mitosis?

• Sister chromatids begin to separate/move apart

• Each sister chromatid is now considered an individual chromosome

What happens in Telophase in Mitosis?

• Chromosomes begin to decondense into chromatin

• Nuclear envelope reforms

• Nucleolus becomes visible

• Spindle fibers break apart

What happens in Cytokinesis?

the cytoplasm divides and makes two cells

What happens in Cytokinesis in Animal Cells?

The cell membrane is drawn inward until cytoplasm pinched in 2 equal parts

What happens in Cytokinesis in Plant Cells?

cell plate forms halfway between divided nuclei

Does the cell cycle happen randomly?

No

Can the cell cycle (growth or division) be turned on or off?

Yes (this is done by internal and external regulators)

What are Internal Regulators?

Proteins that allow the cell cycle to proceed only when certain things in the cell have occurred

What is an example of an internal regulator?

Cyclins (they regulate the timing of the cell cycle in eukaryotic cells)

What are external regulators?

Proteins that respond to events outside the cell

• Direct the cells to speed up or slow down the cell cycle (controls can be turned on or off)

• Important for embryonic development (baby development) and wound healing

What are examples of external regulators?

• Growth Factors - stimulate growth and division

• Contact inhibition - cells stop dividing when they come into contact with neighboring cells

What is contact inhibition?

when cells stop dividing when they come into contact with neighboring cells

(cancer cells do not respond do this external regulator and this leads to uncontrolled cell growth)

What is Apoptosis?

• Programmed cell death

  • happens when things aren’t right in the cell

    • Goal: eliminate dangerous mutations

    • When apoptosis doesn’t function properly…

      • Can lead to cancer because damaged cells multiply rapidly

      • Then these mass of cancer cells become a tumor

Why is there uncontrolled cell division in cancerous cells?

• They do not respond to the signals that regulate cell growth and division

  • Due to a defect in genes that produce the proteins that become regulators

    • Gene defects could be from tobacco use, radiation, other defective genes, viral infection

• P53 - a gene that is commonly defective in cancer cells

  • Normally, it stops the cell cycles until all chromosomes have been
    replicated

  • Because of the defect in this gene, cells lose info needed to respond to signals that regulate

  • Then leads to rapid, uncontrolled cell division

    • leads to a mass of cells called a tumor

What is the gene that is commonly defective in cancer cells?

P53

What are stem cells?

undifferentiated cells (lack a specific job or function)

What are specialized cells?

They perform one job and have physical and chemical differences that allow them to perform one job. (they get this job during cellular differentiation)

What are the benefits of stem cells?

Stem cells are helping to develop a new field of regenerative medicine, in which undifferentiated cells are used to repair or replace damaged cells and tissues.

Scientists have found adult stem cells in various tissues and are also able to revert some specialized cells back

What is a diploid cell and what cells are diploid cell in our bodies?

Diploid cell means that we have 2 sets of chromosomes (2n) and somatic cells in our body have 2 sets of chromosomes.

What is a haploid cell and what cells are haploid in our bodies?

Haploid cell means that we have 1 set of chromosomes in and gametes (sex cells: sperm, eggs) in our body have 1 set of chromosomes.

How many chromosomes does a gamete have if a normal, somatic (body) cell has 22 chromosomes?

11 chromosomes (This is because gametes are haploid (n) meaning they have only one set of chromosomes. Somatic (body) cells are diploid and they have 2 (2n) set of chromosomes)

What organelle in the cell makes the spindle fibers which is used to split the sister chromatids apart?

centrioles

What is a zygote?

A single cell that is the result of the fusion of the sperm and the egg. Then this zygote keeps dividing and becomes a blastocyst. It then becomes an embryo. Its next stage is a fetus.

What does Mitosis and Meiosis mean?

the splitting of the nucleus

Does mitosis occur in prokaryotes?

No (Why? Because prokaryotes lack a nucleus. Mitosis and Meiosis both refer to the splitting of the nucleus and because there is not nucleus in a prokaryotic cell, it just goes through binary fission for reproduction.

What is the G0 stage in cell division?

Rest Stage (the cells are active, just not preparing for division. It also happens when conditions are not favorable for division. Ex. neurons)