the cell cycle, mitosis, and meiosis unit 1

The cell cycle, mitosis, and meiosis

I. Cell Division and the Cell Cycle


A. Why do cells divide?

1. large cells have difficulty transporting enough nutrients across their membrane

2. Cells are limited in size by their SURFACE AREA and VOLUME ratio


B. Cell division

1. the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells


2. Cell cycle and division in prokaryotes

a. prokaryotic cells divide by binary fission

b. Happens in three stepsi. DNA replication happens just before the cell divides, its

DNA is copied

ii. chromosome segregation, the two chromosomes segregate, or separate, and move to opposite ends of the cell

iii. Separation a new plasma membrane starts growing into the center of the cell, and the cytoplasm splits apart, forming two daughter cells


3. Cell cycle and division in eukaryotes

a. It occurs it two main phases mitosis and interphase

b. Interphase lead up to mitosis and has three major phasesi. Growth Phase 1 (G1): during this phase, the cell grows

rapidly, while performing routine metabolic processes

ii. Synthesis Phase (S): during this phase, the cell’s DNA is copied in the process of DNA replication

iii. Growth Phase 2 (G2): during this phase, the cell makes final preparations to divide


c. Control of the cell cyclei. The cell cycle is controlled by regulatory proteins at three

key checkpoints in the cycle

ii. The proteins signal the cell to either start or delay the next phase of the cycle


C. Cancer

1. is a disease that occurs when the cell cycle is no longer regulated

2. Cancer cells grow rapidly and may form a mass of abnormal cells called a tumor

a. The cells take up nutrients and space that normal cells need, this can damage tissues and organs and eventually lead to death

The cell cycle, mitosis, and meiosis

II. Chromosomes and Mitosis


A. Chromosomes

1. Chromosomes are the form of the genetic material of a cell during cell division only the rest of the time DNA is known as chromatin

2. Chromosomes contain

genes, which code for

proteins


3. they are too dense to do any work only purpose to ensure all DNA is transferred to daughter cells


3. Human Chromosomes

a. Human cells normally have two sets of chromosomes, one set inherited from each parent

b. 23 chromosomes in each set, for a total of 46 chromosomes per cell

c. Each pair are known as homologous chromosomes


B. Mitosis

1. Prophase

a. chromatin condenses into chromosomes

b. the nuclear envelope breaks down


2. metaphase

a. spindle fibers attach to the centromere of each pair of sister chromatids

b. the sister chromatids line

up at the center of the cell


3. anaphase

a. sister chromatids separate and the centromeres divide


4. telophase

a. the chromosomes begin to uncoil and form chromatin

b. The spindle also breaks down

c. new nuclear membranes form


C. Cytokinesis

1. the cytoplasm splits in two and the cell divides

The cell cycle mitosis and meiosis

III. Reproduction and Meiosis


A. Reproduction

1. is the process by which organisms give rise to offspring

a. It is one of the defining characteristics of living things


2. Asexual reproduction

a. involves a single parent

b. It results in offspring that are genetically identical to each other and to the parent

c. All prokaryotes and some eukaryotes reproduce this way

d. Asexual reproduction can be very rapid


e. Happens 3 waysi. Binary fission occurs when a parent cell splits

into two identical daughter cells of the same size


ii. Fragmentation occurs when a parent organism breaks into fragments, or pieces, and each fragment develops into a new organism


iii. Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell while it grows and develops


3. Sexual reproduction

a. involves two parents

b. parents produce reproductive cells—called gametes which are haploid cells

c. The process in which two gametes unite is called fertilization

d. The fertilized cell that results is referred to as a zygote which are diploid cells


e. Meiosis

i. Meiosis Ia. Prophase I

1. The nuclear envelope begins to break

down, and the chromosomes condense

2. homologous chromosomes pair up,

which is unique to prophase I


b. Metaphase I1. Spindle fibers attach to the paired homologous

chromosomes

2. The paired chromosomes line up along the

equator of the cell,

this occurs only in metaphase I


c. Anaphase I:

1. the chromosomes of each homologous pair

start to separate from each other

2. the chromosomes moves toward the

opposite poles.


d. Telophase I and Cytokinesis

1. The spindle breaks down, and new nuclear membranes form

2. the cytoplasm of the cell divides, and two

haploid daughter cells result

3. The daughter cells each have a random

assortment of chromosomes, with one from

each homologous pair, both daughter cells go

on to meiosis II


ii. Meiosis II

a. Prophase II i. The nuclear envelope breaks down and the

spindle begins to form in each haploid

daughter cell


b. Metaphase II

i. Spindle fibers line up the sister

chromatids of each chromosome

along the equator of the cell


c. Anaphase II

i. Sister chromatids separate and move to

opposite poles


d. Telophase II and Cytokinesis

i. The spindle breaks down, and new nuclear membranes form

ii. The cytoplasm of each cell divides, and four

haploid cells result.

iii. Each cell has a unique combination of

chromosomes.


f. Gametogenesis

i. The development of haploid cells (from meiosis) into gametes

ii. This is another step the cells must take to be ready for fertilization

iii. in humans the male gametes are sperm and female are eggs


g. Sexual Reproduction and Genetic Variation happens in three ways

i. Crossing over- the exchange of genetic material between non-sister chromatids of homologous chromosomes

ii. Independent assortment- homologous chromosomes are randomly distributed to daughter cells

iii. Two gametes- with different genes from each of the parents involved


h. life cycle

i. is the sequence of stages an organisms goes through from one generation to the next.

ii. Haploid, diploid, and alternation of generations.

the cell cycle, mitosis, and meiosis unit 1

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