Chapter 7: Cellular Reproduction



Chapter 7: Cellular Reproduction

Cell Cycle and Mitosis

1. All cells in your body came from 1 cell – a fertilized egg

a. All new cells contain cytoplasm, organelles and nucleic acids – which are needed for the cell to survive and function

b. The orderly processes that occur during cellular division ensure that cell reproduction is always carried out correctly

2. Phases in the life of a cell are called the cell phase

a. Interphase

b. Prophase

c. Metaphase

d. Anaphase

e. Telophase

3. Interphase

a. Longest phase

b. Used to be called resting phase

i. Actually very busy phase

c. Cells carry out all their usual functions, i.e. respiration, enzyme production, grow and develop into mature functioning cells

d. G1: number of organelles and the amount of cytoplasm in the cell increases

e. S: chromosomes replicate

i. Replication is the process of copying genetic material

1. results in 2 identical sets of chromosomes

ii. chromosomes: a condensed bundle of chromatin that appears during cell division; contains the DNA of the cell

iii. sister chromatids: are identical copies of each chromosome that result from replication

1. remain attached to each other at a point called a centromere

2. chromosomes must replicate during Interphase so that there will be a complete copy of each chromosome in each new cell

f. G2: cell makes organelles and substances it needs for cell division

g. Chromosomes too thin and tangled to be seen during interphase

4. Cell division

a. 2 main steps

i. Mitosis: a series of phases in cell division in which the nucleus of a cell divides into 2 nuclei with identical genetic material

1. occurs only in eukaryotes

ii. Cytokinesis: during which the cytoplasm of the cell divides into 2 new cells, called daughter cells

1. each daughter cell receives 1 of 2 nuclei

Mitosis + Cytokinesis + Mitotic Cell Division

2. daughter cell nuclei are identical to the parent cell nucleus in every way

b. Multicellular organisms grow as more cells repeat the cycle of cell division and growth

c. In some cells Cytokinesis may not occur at all

i. Some muscle cells repeated mitosis with no Cytokinesis forming multinucleated cells/fibers

5. Mitotic Cell Division and Cytokinesis

a. Chromosomes are ordinarily transparent and invisible

b. 1880s Walther Fleming found a way to stain nucleus

i. chromosomes mean “colored bodies”

c. Interphase: chromosomes replicate, cytoplasm increases

i. G1, S, G2

d. Prophase: sister chromatids condense and become thicker ( can be viewed with a microscope); nucleolus and nuclear envelope disappear; microtubules that make up spindle fibers begin to assemble

e. Metaphase: chromosomes move to the center of cell by spindle fibers; attached by centromeres

i. 2 sister chromatids of each chromosome are attach to spindle fibers radiating from opposite ends of cell

f. Anaphase: centromeres of each chromosome pulled by spindles toward ends of cell

i. Sister chromatids have been separated

g. Telophase: new nucleus begins to form around the chromosomes at each end of cell

i. Mitosis now complete

ii. Cell membrane begins to pinch the cell in two as Cytokinesis begins

h. Cytokinesis: completes the process of cell division

i. During Cytokinesis the cytoplasm of a cell and it’s organelles separate into 2 daughter cells

ii. Animals: cytoplasm divides when a groove called a cleavage furrow forms through middle of parent cell

1. Cleavage furrow deepens until parent cell is pinched “in two”

iii. Plant: material for cell walls and membranes gather and fuse along the equator or middle of the cell – between the 2 nuclei

6. Control of Mitosis

a. Cancer: cells begin to divide, grow and change abnormally

i. Tumors and cancer – results in growth and spread of abnormal cells

ii. Causes: heredity, certain chemicals, radiation etc.

iii. Tumor: abnormal growth

1. Can be benign or malignant

a. Benign: cells remain together, usually cause little harm

b. Malignant: cells do not remain together; may break free from the tumor; migrate to new locations and start new tumors

iv. Cancer: spread of malignant cells to new locations

1. cancer cells can spread freely because they lack the surface protein that bind normal cells together

2. Cancer was once thought to be disorganized cell growth

a. Now: cells acquire abnormal size, shape and abilities to invade normal

b. tissue and replace healthy cells

b. Normal growth and repair

i. Multi-cellular organism grows as its cells produce new cells by mitosis and new cells grow larger

1. some change to take on specialized shapes and functions

2. differentiation: changes that take place in cells as they develop

a. contact between new cell and surroundings cells help determine what kind of cell the new cell will become

ii. in most animals, mitosis stimulated by chemicals called growth factors

1. most are highly specific

2. cause mitosis in only 1 type of cell

3. growth factors are “chemicals that stimulate the division and differentiation of new cells during growth ‘

a. also stimulate cell division when new cells are needed to replace injured ones

b. regeneration: process of growing back lost body parts

i. some animals can regenerate

ii. cells at site of wound become less specialized and divide

iii. new cells differentiate to become bone, muscle, nerve, skin

iii. asexual reproduction: “reproduction in which one parent produces offspring by cell division”

1. produces new individual that has DNA identical to DNA of parent

2. common for: bacteria, fungi, plants and some animals

a. budding: new organism grows from piece of another organism

i. parent produces offspring by growing a tiny replica of itself – a bud – on some part of its body

ii. after enough growth, the bud separates from the parent and becomes independent

b. fragmentation: separate pieces of parent organism can develop into new organisms

i. flatworm can pinch itself :in two” – each part can develop into a new organism

ii. sea star – if torn apart, each part with a piece of the central ring can develop into a separate individual

c. vegetative reproduction: new plant grows from stem, root or leaves of an existing plant

i. contain exact same DNA as original plant

Meiosis and Sexual Reproduction

1. Sexual reproduction – “when the chromosomes of 2 parent s combine to produce offspring

a. Gametes - “chrosomes that combine during sexual reproduction are contained in special reproductive cells called gametes”

i. Female gamete – egg – large, lots of cytoplasm

ii. Male gamete – sperm – small, little cytoplasm, flagella

b. Chromosomes of 2 gametes join

i. Chrosomes number in parent and zygote must match

2. Meiosis; production of gametes

a. A type of cellular reproduction

b. Occurs only in eukaryotes

c. Differs from Mitosis:

i. Produces daughter cells that have ½ the number of chromosomes of parent cell

ii. Daughter cells not all alike due to the way cell divides during meiosis – the cells may have different chromosomes from each other

iii. Number of cells produced is different

1. in mitosis – 1 parent cell produces 2 daughter cells

2. in meiosis – 1 parent cell produces 4 daughter cells

d. chromosome number – every gamete contains 1 complete set of chromosomes

i. considered complete because together the chromosomes contain all the information needed for organism to function properly

ii. in humans – each gamete has 23 chromosomes

1. all other body cells have 46 chromosomes

iii. diploid: any cell that contains 2 complete sets of chromosomes – 1 donates by “mom” and 1 donated by “dad”

iv. number of chromosomes in diploid cell is called the diploid number

1. represented by the notation 2N

2. every organism has characteristic diploid organism has characteristic diploid number

a. not related to its complexity or size

v. haploid: a cell with only 1 complete set of chromosomes

1. represented by the notation N

e. Fertilization – when an egg cell and a sperm cell of the same type of organism join to produce a new individual

i. Zygote – single cell that results from fertilization

1. contains 2 complete sets of chromosomes

2. chromosomes exist is pairs – 1 from each gamete

3. Homologous pairs – matching pairs of chromosomes in a diploid cell

4. both chromosomes in a homologous pair code for the same traits

3. Phases of Meiosis

a. Meiosis – number of chromosomes in each cell is reduced from diploid to haploid by separating homologous pairs of chromosomes

b. 2 main stages

i. Meiosis I – homologous pairs separate

ii. Meiosis II – sister chromatids of each chromosome are separated

c. Meiosis I – at the start: each chromosome consists of 2 strands of sister chromatids connected by a centromere

i. Prophase I

1. chromosomes become thick and visible

2. chromosomes of each homologous pair become tangled

3. each pair consists of 4 chromatids – because each chromosome in the pair has replicated before meiosis began

4. by the end of prophase I, nucleoli and nuclear envelope have disappeared

5. spindle fibers are forming

ii. Metaphase I

1. homologous chromosomes are still together

2. pairs of chromosomes are arranged in the middle of the cell

iii. Anaphase I

1. homologous pairs separate from each other

2. spindle fibers pull 1 member from each pair to opposite ends of the cell

3. each chromosome still consists of 2 sister chromatids

iv. Telophase I

1. new nuclear envelope may or may not form

2. Cytokinesis does occur; each new cell is haploid – containing 1 chromosomes from each pair

d. Meiosis 2

i. Chromosomes do not replicate before beginning second division

ii. Sister chromatids remained attached during 1st meiotic division

iii. Each daughter cell produced during meiosis I divides again during meiosis II

1. sister chromatids of each chromosome separate and are divided between 2 new cells

2. remember, during mitosis sister chromatids are also divided between 2 cells

iv. in animals Mitosis divides chromosomes in a diploid cell; meiosis II divides the chromosomes in a haploid cell

e. crossing over –

i. gene: code for 1 trait or characteristic of the organism

ii. chromosomes contain/carry many genes

iii. crossing over: the exchange of genes between pairs of homologous chromosomes

iv. usually occurs during prophase I of meiosis when homologous pairs are still joined

1. homologous chromosomes break and exchange genes

2. after crossing over, each chromosome in the homologous pair has a different combination of genes than it had before meiosis began

4. Meiosis and Evolution

a. Meiosis results in new combinations of characteristics with a population

b. Evolution is the process of change in living populations over time

c. Variation – differences among members of a population are collectively called variations

i. Result from recombination of genes during meiosis and fertilization

ii. Random separation of homologous pairs of chromosomes produce new combinations of genes

d. Organisms characteristics enable it to survive in its environment

i. Not all characteristics are equally “well suited”

ii. Conditions of environments determine the traits that benefit the survival of an organism and which do not

iii. As environments change, traits that were once beneficial could become a disadvantage

e. Genetic variation rarely occurs from generation to generation among asexual organisms

i. Change in environment could destroy entire population

f. Reshuffling of genes that occur during meiosis ensures a certain amount of genetic variation in a population

i. Variety of traits within the population increase the chance that some individuals will survive the change

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download