Chapter 4 Cell Reproduction

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Cell division occurs

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to make many cells in a multi-cellular organism; replace cells; and helps one-celled organisms reproduce too.

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Cell Cycle

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Time--Different for all cells

Beans-19 hours

Embryos-less than 20 min

Humans-16 hours

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Interphase

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Where most of eukaryotic cell cycle takes place; cells that no longer divide (nerve & muscle cells) are always in Interphase; In Interphase-- cell grows and functions and organelles duplicate; then, DNA is copied and chromosomes duplicate; Next cell grows and prepares for mitosis; Mitosis occurs; Cytoplasm divide; Nucleolus is clearly visible

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Mitosis

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process in which the nucleus occurs divides to form two identical nuclei with the exact same chromosomes (DNA material

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Steps of Mitosis

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Prophase; Metaphase; Anaphase; and telophase

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Prophase

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Pairs of Chromatids are visible and spindle is beginning to form; Spindle fibers; Duplicated chromosomes; Nucelolus and nuclear membrane disintegrate; centrioles move to opposite ends (Plant cells do not have centrioles) but have spindle fibers

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Metaphase

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Pairs of chromatids line up across the MIDDLE/center of the cell. The centromere of each pair becomes attached to two spindle fibers--one from each cell

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Anaphase

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Centromere divides and spindle fibers shorten; each pair of chromatids separates and chromatids begin to move to opposite ends of the cell. The separated chromatids are now called chromosomes

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Telophase

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Spindle fibers start to disappear and chromosomes start to uncoil, which results in two separate nuclei--then enter interphase and cell division begins again

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Cell Division

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for most cells--after nucleus divides; the cytoplasm separates and two new cells form; In animal cells--cell membrane pinches in middle and separates cytoplasm

In plant cells, a cell plate divides the cytoplasm allowing a new cell wall to develop and molecules are released by cell membranes

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Important things about Mitosis

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1) Mitosis is the division of a nucleus

2) Mitosis produces two new nuclei that are identical to each other and the original nucleus

3) The original cell no longer exists

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Chromosomes in each cell in body

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46 (23 pairs) in all cells except sex cells

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Cell division allows

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growth

replaces worn out or damaged cells

allows you to heal

produce new organisms

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Asexual vs. Sexual Reproduction

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Sexual Reproduction-requires two individuals to produce offspring

Asexual, a new organism is produced from one organism and will have same hereditary material as parent

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Cellular Asexual Reproduction

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Organisms with eukaryotic cells asexually reproduce by mitosis and cells division--Sweet potato in water grows stems, leaves and roots; strawberry plants produce runners

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Bacteria

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Bacteria cannot use mitosis so it uses FISSION

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Fission

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One-celled bacterium without a nucleus copies its genetic material and then divides into two identical organisms

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Budding

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A new organism is growing from the body of parent organism. Type of asexual reproduction made possible because of mitosis and cell division--HYDRA is example; Bud on adult becomes large enough and breaks away

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Regeneration

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process that uses mitosis and cell division to regrow body parts--sponges; plan aria, sea stars use regeneration for asexual reproduction. If a star fish breaks into pieces, a new organism grows from each piece.

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Sexual Reproduction

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two sex cells--egg and sperm come together

Generally egg/sperm come from two different organisms of the same species--two humans; two dogs; two birds

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Sperm

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formed in male reproductive organs

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Egg

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formed in female reproductive organs

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Fertilization

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joining of egg and sperm

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Zygote

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Cell that forms from fertilized egg/sperm

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Body vs. Sex Cells

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Body cells--outnumber sex cells (ex of body cells--skin, bones, brain)--each having 46 chromosomes (23 pairs)--Diploid

Sex Cells--have only half (23)--Haploid--single form

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Diploid Cells

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pairs of similar chromosomes

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Haploid Cells

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Single form

Sex cells do not have pairs of chromosomes--they only have half the number of chromosomes as body cells

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Meiosis

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produces haploid sex cells

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If two diploid cells combined

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organism would have twice as many chromosomes as parent--most animals do not survive with twice as many; however, some plants can survive

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Meiosis

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ensures the offspring has the same diploid number as its parent; After two haploid sex cells combine; a diploid zygote is produced that develops into a new diploid organism

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Meiosis

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Two divisions of the nucleus occurs: Meiosis I and Meiosis II

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Meiosis I

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1) Each chromosome duplicates as two chromatids

2) Prophase I--pair of duplicated chromosomes appear; chromatid pairs are are now visible; spindle fibers begin to form

3) Metaphase II-paris of duplicated chromosomes line up in center of cell-

4) Anaphase I--centromere of each chromatid becomes attached to one spindle fiber so chromatids do not separate; each duplicated chromatid pair moves to opposite ends of the cell

5) Telophase I--cytoplasm divides and two new cells form--each new cell has one duplicated chromosome from each similar pair

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Meiosis II

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1) Two cells formed in Meiosis I and chromosomes from each duplicated chromosome become separated

2) Prophase II-duplicated chromosomes and spindle fibers reappear in each new cell

3) Metaphase II--duplicated chromosomes move to the center of cell and each centromere attaches to two spindle fibers instead of one

4) Anaphase II--centromere divides; chromatid separates and move to opp. ends of cell; each its own chromosome

5) Telophase II--spindle fibers disappear; nuclear membrane forms around each set of chromosomes; when done cytop. divides

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Summary of Meiosis

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Meiosis I-two cells form

Meiosis II--both of the cells form two new cells, resulting in 4 sex cells--each having half the number of of chromosomes in its nucleus that was in the original nucleus

A human cell with 46 paired chromosomes--produces 4 sex cells each with 23 unpaired chromosomes

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Human--You

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received haploid from mom and haploid from dad making you a diploid

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Polyploid

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having 3, 4 or more sets of chromosomes

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Triploid

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Banana--cannot reproduce sexually and have small seeds of any

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Hexaploid

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Oats have six sets of chromosomes, massing them hexaploid

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Tetraploid

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Peanuts, daylilies

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Octaploid

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larger leaves, flowers or fruit--example of octaploid-strawberry--have 8

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Mistakes in Meiosis

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Like in plants--when in sex cells, sometimes the zygote (egg and sperm) dies; or the organism may not grow normally

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DNA

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deoxyribonucleic acid--code in hereditary information; When cell divides-DNA code is copied; each cell that has been formed contains DNA

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Discovery of DNA

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Since 1800's scientist knew nuclei of cells contain large molecules called nucleic acid

1950's chemist learned what nucleic acid was made of but didn't understand how parts of DNA were arranged

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DNA

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double helix--looks like a twisted ladder and made of sugar phosphate molecules

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DNA rungs

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are pairs nitrogen bases paired together like a puzzle

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1952

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Rosalind Franklin discovered DNA is two chains in spiral form

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1953

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Franklin, James Watson and Francis Crick made a model of DNA molecule

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Watson and Crick DNA

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each side of ladder is made of sugar phosphate molecules

sugar-deoxyribose & a phosphate group

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4 Nitrogen bases (rungs of ladder)

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Adenine-A

Guanine-G

Cytosine-C

Thymine-T

that pair up

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How do the nitrogen bases pair up

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Cytosine always with Guanine (CG)

Adenine always with Thymine (AT)

Like a puzzle--always with its partner

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Copying DNA

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Before Mitosis/Meiosis--DNA in nucleus is copied

Watson and Crick--two sides of DNA unwind and separate; each side then becomes a pattern for the new side to form. The new side has the identical bases in the same order

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DNA

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contains instructions for your hair color, eye color, height, etc.

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Genes

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Instructions for making a specific protein are found in genes, which is a section of DNA on a chromosome

Each chromosome contains hundreds of genes

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Protein

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Chains of hundreds/thousands of amino acids; gene determines order of amino acids in a protein--changing the order makes a different protein

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Human Chromosome 7

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Genes which occur: Diabetes, Williams Beuren Syndrome (physical/mental dev. disorder); Cystic Fibrosis; Pendred Syndrome (form of deafness); Obesity

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Making Proteins

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Proteins are made on ribosomes in cytoplasm

Codes for making proteins are carried from nucleus to ribosomes by ribonucleic acid--RNA

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RNA

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made in nucleus on a diff. pattern than DNA

RNA is like a ladder with all of its rungs cut in half

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RNA nitrogen bases

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Adenine

Guanine

Cytosine

Uracil (replaces thymine)

CG

AU

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3 types of RNA

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mRNA-messenger RNA

rRNA-Ribosomal RNA

tRNA-Transfer RNA

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Role of RNA

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Protein production begins when mRNA moves into cytoplasm and ribosomes attach to it (rRNA)--ribosomal RNA

Then tRNA molecules in the cytoplasm bring amino acids to ribosomes

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RNA cont'd

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mRNA and another tRNA match

amino acids that are attached to two tRNA molecules bond--beginning of a protein

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mRNA

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code directs order in which amino acids bond, After tRNA loses its amino acid, it moves to cytoplasm to pick up another amino acid. Ribosomes move along the mRNA. New tRNA molecules with amino acids match up and add amino acids to protein molecule

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Controlling Genes

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Each cell uses only the genes that direct the making of proteins that it needs

Cells must be able to control genes by turning some off and others on. By not having control, organism cannot function properly

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Mutations

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DNA is not copied exactly or not made correctly

Mistakes; permanent changes in DNA sequence of a gene or chromosome of a cell

Some receive an extra chromosome or are missing a chromosome

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Results of Mutations

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Organism may not be able to grow, repair or maintain itself. Defect of a fruit fly may result in shorter wings, not allowing it to fly.

May be life threatening to organism

If mutation is in sex cell, all cells formed from that sex cell will have mutation

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Mutations Con't

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Mutations add variety to a species and some are harmful, often causing death

A mutation could be helpful if a plant has a mutation and makes a chemical insects don't like--the plant will grow and insects won't eat it (benefit)

Albino (white) deer might have a mutation and won't be camouflaged in the woods, making it easier to be seen/shot.

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Mutations

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Mutations can result in dominant genes or recessive genes (recessive means it will only appear if an organism has two recessive genes for the trait). A dominant gene can show the mutation if one or two of the genes are shared.ifL

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Life Cycle of a Cell

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Cell has two parts--grown and development & cell division