Cell Reproduction 8.1 – Chromosomes 8.2 – Cell Division 8.3 - Meiosis.
-
Upload
liliana-douglas -
Category
Documents
-
view
240 -
download
0
Transcript of Cell Reproduction 8.1 – Chromosomes 8.2 – Cell Division 8.3 - Meiosis.
Cell Reproduction
8.1 – Chromosomes
8.2 – Cell Division
8.3 - Meiosis
What factors limit cell size? Diffusion
DNA Content
Surface area-to-volume ratio
DIFFUSION Certain materials needed for the survival of the
cell can only enter through diffusion.
Ex. waste, carbon dioxide, oxygen
Diffusion is only efficient over a short distance. A 20 cm cell would have to wait several months
to receive the above listed molecules
DNA CONTENT Most cells have only 1 nucleus
The DNA in the nucleus makes RNA and releases it to the cytoplasm where it directs the production of enzymes
Lack of enzymes = Lack of cellular metabolism
Some large cells have compensated by having multiple nuclei.
Surface area-to-volume ratio If you double the size of a cell…
-It has 8x as much volume
-Gives rise to 8x as much waste and need for nutrients
-It becomes impossible for diffusion to keep up with the cellular demands
Chromosomes
Rod-shaped structures made of DNA and protein Coiled chromatin
=chromosomes Histones = proteins that help
maintain the shape of the chromosome
Types of Chromosomes
Sex Chromosomes X or Y chromosomes Determine sex of individual
Autosomes Non-sex chromosomes Determine all other characteristics or
traits Ex. Hair color, eye color, hemophilia
Chromosome Number
Diploid Having 2 sets of chromosomes (2n) Creates genetic diversity
Hapliod Contain one set of chromosomes (n) Sex cells
Two major stages of the cell cycle
Interphase – the growth period of time where cell activities are carried out
-most of the cells life
Mitosis – process of nuclear division, followed by the division of the cytoplasm
INTERPHASE What is going on during this time?
G1 Phase Metabolism – making ATP Cell growth, maintenance, repair
S Phase Chromosomes are replicated (ready for mitosis) Make new proteins Synthesizing new organelles Conducting photosynthesis (autotrophs) Storing excess glucose (starch, glycogen)
G2 Phase Final preparation before cell division (mitosis)
Stages of Mitosis Prophase Metaphase Anaphase Telophase
PROPHASE First stage of mitosis
Longest phase of mitosis Chromatin the nucleus becomes visible
chromosomes Nucleus disappears The chromatin, which was copied during
interphase forms 2 complete sets of chromosomes called sister chromatids
Spindle fibers form between pairs of centrioles
METAPHASE Second stage of mitosis
Chromosomes move to the equator of the cell Spindle fibers attach to each chromatid by its
centromere
ANAPHASE Third stage of mitosis
Chromosomes separate at the centromere Each sister chromatid begins to move to opposite
ends of the cell
TELOPHASE Fourth stage of mitosis
Two daughter cells are formed Each new cell has a complete set of chromosomes The cytoplasm then divides (cytokinesis) Nucleus reappears Chromosomes uncoil to form chromatin Interphase begins
Control of the Cell Cycle Cellular enzymes and genes play a key role in
checking and balancing cell division
Tells cells when to divide/stop
Proto-oncogene – regulates cell growth, division and the ability for cells to adhere to one another
Mutation of the proto-oncogene causes an oncogene ONCOGENE = UNCONTROLLED CELL DIVISION
Control of the Cell Cycle (2)
Contact inhibition – cell to cell communication between neighboring cells…stops the cellular division Eliminates an over-production of certain types of
cells within the body.
CANCER – a loss of control Cancer – an uncontrolled dividing of cells
Caused by a change in one or more of the genes synthesizing enzymes to control the cell cycle (genetic factor)
The cancer genes are often expressed when environmental conditions change (environmental factor)
How can cells regain control Some genes act as brakes to suppress
cancer expression Tumor-suppressor genes – code for
proteins that prevent cell division from occurring too often To get cancer, these tumor suppressor genes
(all 3 of them) must be damaged
Carcinogen Any substance that can induce or promote
cancer Most carcinogens are mutagens
Cause mutation within the cell
Known carcinogens include: Chemicals in tobacco smoke Radiation UV light Certain viruses
MEIOSIS
INTERPHASE
INTERPHASE MAIN EVENTS
Chromatin replicates Just like in mitosis Forms 2 identical chromatids
Centriole pairs replicate (animal cells only)
PROPHASE I
PROPHASE I MAIN EVENTS
Chromatin condenses into chromosomes Tetrad forms by synapsis Crossing over occurs between
homologous chromosomes Centriole pairs move apart Nuclear envelope and nucleoli disappear
METAPHASE I
METAPHASE I MAIN EVENTS
Tetrads align along the metaphase plate Centromeres of homologous
chromosomes point toward opposite poles
Attach to spindle fibers
ANAPHASE I
ANAPHASE I MAIN EVENTS
Homologous chromosomes separate
Sister chromatids move as a unit remain attached at the centromere
TELOPHASE I AND CYTOKINESIS
TELOPHASE I MAIN EVENTS
Chromosomes reach poles Still as sister chromatids
Cytokinesis occurs simultaneously Interkinesis No DNA replication before meiosis II
MEIOSIS II MAIN EVENTS
Very similar to mitosis PII – spindles form MII – chromosomes align AII – centromeres split TII – nuclei reform Cytokinesis – 4 haploid cells
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II AND CYTOKINESIS
KEY DIFFERENCES BETWEEN MEIOSIS AND MITOSIS…
Meiosis is reduction division 2n to n
Meiosis creates genetic variation Meiosis is 2 successive nuclear
divisions Meiosis I separates pairs of
chromosomes; centromeres do not divide
GAMETE PRODUCTION THROUGH MIEOSIS
Spermatogenesis Creates 4 sperm cells
Oogenesis Creates 1 ootid (egg cell) 3 polar bodies (nonfunctional)
ASEXUAL REPRODUCTION
Production of offspring from one parent without the union of gametes
Occurs only by mitosis
SEXUAL REPRODUCTION
Production of offspring through meiosis and the union of gametes
Offspring genetically different due to genetic recombination Parts of chromatids can be exchanged
(crossing over) Homologous pairs separate