cell growth & division: mitosis. i. chemical pathways cell growth and division a. limits to cell...

Cell Growth & Division: Mitosis

I. Chemical Pathways

Cell Growth and Division

A. Limits to Cell Growth (two main reasons why cells divide)

1. DNA “Overload”

b. Creates “information crisis” (too much Cell, too little DNA!)

a. The larger the cell gets, the bigger the demand on its DNA (DNA found in the nucleus of the cell)

2. Exchanging Materials

a. Rate of exchange of materials (food, water, wastes) depends on the surface area of the cell)b. Rate at which food and oxygen are used up depends on cell’s volume

c. Ratio of surface area to volume- when cell grows, volume increases faster than it’s surface area.

3. Cell Division- to solve the problem of small surface area to volume, a cell divides into two daughter cells

a. Cell replicates (copies) it’s DNA before divisionb. Rates vary from 30 minutes (bacteria) to many decades

Concept 9.1 - All cells come from cells

• The division of cells into more cells enables living things to repair damage, to grow and to produce offspring

Cell Repair & Growth

• Enables your body to produce new cells to replace dead cells

Reproduction

• Asexual– Single cell duplicates its genetic material and

splits into 2 genetically IDENTICAL cells

• Sexual– Genetic material from each of 2 parents

combine, producing offspring that differ genetically from either parent

Asexual Reproduction

• Asexual reproduction is the formation of offspring from one parent

• Offspring produced by asexual reproduction are genetically identical to the parent

Binary fission is the process of cell division in prokaryotes

Concept 9.2 – The cell cycle multiplies cells

• At this moment, millions of cells in your body are dividing, each forming 2 new cells.

Chromosomes

• Almost all of the genes of a eukaryotic cell are located in the nucleus.

• Most of the time, this genetic material exists in long fibers too thin to be seen under a light microscope.

• As a cell prepares to divide – these fibers condense and become visible as chromosomes.

Chromosomes

• Chromosomes are tightly coiled DNA molecules and associated proteins

• In eukaryotes, histone proteins help maintain the compact structure of chromosomes

DNA

Histone

• In dividing cells, chromosomes are composed of 2 identical chromatids constricted together at a centromere

• Chromosomes are categorized as either sex chromosomes or autosomes

Sex Chromosomes

• Homologous chromosomes consist of one autosomal chromosome from each parent

II. Cell Division

A. Chromosomes- genetic information carried on chromosomes

1. Before cell division each chromosome is replicated (copied)

2. Each chromosome consists of two identical “sister” chromatids

3. Each pair of chromosomes attached to area called centromere

Cell Cycle

• The cell cycle goes from the “birth” of a cell until it reproduces itself.

Cell Cycle• Interphase (**The resting phase)

– 90% of the cell cycle is spent here– Stage where the cell performs its functions

• Increasing proteins, releasing enzymes, etc

– G1, S, and G2 stages• G1 – Gap 1 = Cell growth and activity• S – DNA Synthesis = Genetic material (DNA)

copied• G2 – Gap 2 = Cell prepares to divide; organelles

produced (double in #)

Cell Cycle

• Mitotic Phase– Contains 2 processes

• Mitosis

– Nucleus and duplicated chromosomes divide and are evenly distributed, forming 2 “daughter” nuclei

• Cytokinesis – Cytoplasm is divided into 2

Cell Cycle

• The cell cycle is the repeating of events that make up the life of a cell

• The cell cycle consists of cell division and interphase

Cell Division

Concept 9.3

Cells divide during the mitotic phase

Interphase

• Interphase consists of a phase of growth (G1), a phase of DNA replication (S), and a phase of preparation for cell division (G2)

Mitotic Phase

• Mitosis is divided into: prophase, metaphase, anaphase, and telophase

• ACRONYM: P M A T

• Mitosis results in two offspring cells that are genetically identical to the original cell

C. Mitosis- Division of Cell Nucleus and Cytokinesis. Divided into 4 phases

1. Prophase- First and longest phase.

• Chromosomes become visible

• Centrioles separate and migrate to opposite sides of nucleus

•Chromosomes attach to spindle fibers.

•Nuclear membrane breaks down

2. Metaphase- Chromosomes line up across the center of the cell

3. Anaphase-

•Centromeres that join chromatids separate.

•Sister chromatids separate

•Chromosomes moves to opposite poles

4. Telophase-

•Condensed chromosome begin to disperse

•Nuclear envelope re-forms around cluster of chromosomes

•Nucleolus becomes visible

D. Cytokinesis- division of cytoplasm following mitosis

1. Animal cells- cell membrane drawn inward until cytoplasm is pinched into two nearly equal parts

2. Plant cells- cell plate forms midway between divided nuclei. Gradually develops into separating membrane. Eventually cell wall begins to appear.

Cytokinesis

• The process by which the cytoplasm divides and one cell becomes two individual cells

• Animals - cell pinches inward

• Plants - a new cell wall forms between the two new cells

Mitosis Summary

Concept 9.4 – Cancer cells grow and divide out of control.

• Timing during normal cell division is critical to normal growth and development.

• When the “control system” malfunctions, cells may reproduce at the wrong time or in the wrong place.

III. Regulating the Cell Cycle

A. Controls on Cell Division

1. Protein called cyclin regulates the timing of the cell cycle in eukaryotic cells

2. Cells will grow in petri dish until they come into contact with other cells. Cell growth turned “on” and “off”

3. Two main types of regulatory proteins

a. Internal regulator- respond to events inside the cell. (e.g. Cell will not enter mitosis until all chromosomes replicated.

b. External regulator- respond to events outside the cell. (e.g. Wound healing and embryonic development.) can also prevent excessive cell growth

B. Uncontrolled Cell Growth

1. Cancer- do not respond to signals that regulate growth of most cells. Form masses called tumors

2. Don’t respond to external growth regulators. Some may be genetic.

Tumors & Cancer

• Benign tumors – Abnormal mass of essentially normal cells– Depending on their location they sometimes cause health

problems– Often removed via surgery

• Malignant tumors– Masses of cells that result from reproducing cancer cells– Cancer disrupts the timing of cell division – this disruption

leads to uncontrolled cell division

• Metastasis– Spread of cancer beyond its original site

Spread of cancer cells in breast cancer

Metastasis

Cancer Treatment• When possible, malignant tumors are removed with

surgery

• To treat cancer on the cellular level – radiation and chemotherapy is often used– Radiation exposes the cells to high energy radiation,

which disrupts cells division– Chemotherapy involves treating patients with cytotoxic

chemicals which prevent cell division• Different types of chemotherapy drugs affect cell division in

different ways (preventing the spindle fibers from forming, “freezing” the spindle, etc)

Cancer Treatment• Radiation & Chemotherapy often causes

undesirable side effects in normal body cells that rapidly divide– Radiation can affect ovaries & testes – and can cause

sterility– Chemotherapy often damages intestinal cells or hair

follicles (fast growing cells), causing nausea or hair loss

Cell Growth & Division: Meiosis

Concept 9.5 – Meiosis functions in sexual reproduction.

• Only dogs produce more dogs, only trees produce more trees, and only people produce more people.– BUT: “Like begets similar to, but not exactly like.”

Sexual Reproduction

• Sexual reproduction is the formation of offspring through the union of a sperm and an egg

• Offspring produced by sexual reproduction are genetically different from the parents

I. Meiosis

A. Chromosome number

1. Diploid number- means “two sets”. Represented by symbol 2N. One of each set from mother/father. Sets called homologous chromosomes

a. Diploid cells found in body cells; Human cells = 46 chromosomes

b. Contains two sets of chromosomes and two sets of genes

2. Haploid number- means “one set”. Represented by N.

a. Gametes all haploid; Human sex cells = 23 chromosomes

b. Haploid cells (gametes) produced by meiosis

• Diploid (2n) is the number of chromosomes in cells that have homologous pairs of autosomes and 2 sex chromosomes

Meiosis• Meiosis produces haploid daughter cells from

specialized cells in diploid organisms.

• Despite the similarity in their names, meiosis is different from mitosis in two major ways. – The first major difference is that meiosis produces four

new offspring cells, each with one set of chromosomes—thus half the number of chromosomes as the parent cell.

– The second major difference is that meiosis involves the exchange of genetic material between homologous chromosomes.

Meiosis• Goes through

two divisions – Meiosis 1– Meiosis 2

• During meiosis, a cell divides twice

B. Phases of Meiosis (2 stages)

1. Meiosis I- each chromosome is replicated (copied)

a. Similar to mitosis- but chromosomes line up in pairs- Tetrads in prophase I

b. Exchange of portions of chromatids takes place while chromosomes exist as tetrads. Called crossing-over

c. Results in two diploid daughter cells

1. Meiosis II-

a. No new replication of chromosomes

b. Results in four haploid daughter cells

C. Gamete formation- in animals: egg and sperm

• Spermatogenesis is the process by which sperm cells are produced

• Oogenesis is the process that produces egg cells (ova)

Meiosis and fertilization

It’s easy to see how genes located on different chromosomes assort independently, but what about genes located on the same chromosomes? Wouldn’t they generally be inherited together?

The answer to these questions, Thomas

Hunt Morgan first realized in 1910, is yes!

D. Linkage and Gene Maps

1. Gene Linkage- genes on same chromosome almost always inherited together (unless separated by “crossing over” during meiosis)

a. Experiments by Thomas Hunt Morgan (1910)- research on fruit flies (Drosophila melanogaster)

1). Chromosomes big, only 4 pair, bred quickly2). Concluded: chromosomes assort independently, not the individual genes

b. By luck, 6 of the 7 genes Mendel studied were on different chromosomes (the two genes found on the same chromosome were so far apart that they also assorted independently- due to crossing over)

2. Gene Maps- rate of “crossing over” used to map location of genes on chromosomes

a. Alfred Sturtevant- said further apart the genes were, the more likely they were to be separated during crossover in meiosisb. Gathered data and “mapped” location of genes in Drosophila chromosomesc. Also used to map human genome

Chapter 9

Cell Growth & Division

As a cell becomes larger, its

a. volume increases faster than its surface area.

b. surface area increases faster than its volume.

c. volume increases, but its surface area stays the same.

d. surface area stays the same, but its volume increases.

As a cell grows, it

a. places more demands on its DNA.

b. uses up food and oxygen more quickly.

c. has more trouble moving enough materials across its cell membrane.

d. all of the above

If the length of a cell increases 10 times, its volume increases about

a. 5 times.

b. 10 times.

c. 100 times.

d. 1000 times.

The speed with which wastes are produced by a cell depends on the cell's

a. ratio of surface area to volume.

b. environment.

c. volume.

d. surface area.

Unlike small cells, large cells have more trouble

a. dividing.

b. producing daughter cells.

c. moving needed materials in and waste products out.

d. making copies of their DNA.

When during the cell cycle are chromosomes visible?

a. only during interphase

b. only when they are being replicated

c. only during cell division

d. only during the G1 phase

When during the cell cycle is a cell's DNA replicated?

a. G1 phase

b. G2 phase

c. S phase

d. M phase

Which event occurs during interphase?

a. The cell grows.

b. Centrioles appear.

c. Spindle fibers begin to form.

d. Centromeres divide.

Cell division is represented in Figure 10-1 by the letter

a. A.

b. B.

c. C.

d. D.

The cell cycle is the

a. series of events that cells go through as they grow and divide.

b. period of time between the birth and the death of a cell.

c. time from prophase until cytokinesis.

d. time it takes for one cell to undergo mitosis.

The structure labeled A in Figure above is called the _____________.

a. centromere.

b. centriole.

c. sister chromatid.

d. spindle.

The structures labeled B in Figure above are called

a. centromeres.

b. centrioles.

c. sister chromatids.

d. spindles.

The first phase of mitosis is called

a. prophase.

b. anaphase.

c. metaphase.

d. interphase.

During which phase of mitosis do the chromosomes line up along the middle of the dividing cell?

a. prophase

b. telophase

c. metaphase

d. anaphase

Which of the following represents the phases of mitosis in their proper sequence?

a. prophase, metaphase, anaphase, telophase

b. interphase, prophase, metaphase, anaphase, telophase

c. interphase, prophase, metaphase, telophase

d. prophase, metaphase, anaphase, telophase, cytokinesis

What is the role of the spindle during mitosis?

a. It helps separate the chromosomes.

b. It breaks down the nuclear membrane.

c. It duplicates the DNA.

d. It divides the cell in half.

One difference between cell division in plant cells and in animal cells is that plant cells have

a. centrioles.

b. centromeres.

c. a cell plate.

d. chromatin.

During normal mitotic cell division, a parent cell having four chromosomes will produce two daughter cells, each containing

a. two chromosomes.

b. four chromosomes.

c. eight chromosomes.

d. sixteen chromosomes.

Cancer is a disorder in which some cells have lost the ability to control their

a. size.

b. spindle fibers.

c. growth rate.

d. surface area.

Cancer cells form masses of cells called

a. tumors.

b. cyclins.

c. growth factors.

d. p53.

Meiosis of a cell containing 50 chromosomes would result in

a. 2 sperm cells with 50 chromosomes

b. 2 egg cells with 25 chromosomes/ea.

c. 4 sperm cells with 25 chromosomes

d. None of the above

Meiosis of a cell containing 50 chromosomes would result in

a. 2 sperm cells with 50 chromosomes

b. 2 egg cells with 25 chromosomes

c. 4 sperm cells with 25 chromosomes

d. None of the above

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What is the name of structure (f)?

Centrioles

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What phase is represented by letter (a)?

Interphase

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What phase is represented by letter (j)?

anaphase

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What are structures (c) called?

Spindle fibers

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What phase is represented by letter (d)

metaphase

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What phase is represented by letter (g)

telophase

(j)

(a) (b) (d)

(g)

(c)

(f)

(h)

(i)

(e)

What phase is represented by letter (b)?

Prophase

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