cell division ch 10 & 11 sections 10-2, 10-3 & 11-4
TRANSCRIPT
Cell Division
Ch 10 & 11
Sections 10-2, 10-3 & 11-4
Reproduction of Prokaryotes
Prokaryotes reproduce through a process called binary fission
The single, circular chromosome (which is attached to the plasma membrane) replicates
The cell grows & elongates, separating the two chromosomes
The plasma membrane and cell wall pinch inward, eventually forming two daughter cells
Eukaryotic Chromosomes and Cell Division Almost all of a eukaryotic cell’s genes are
found in the cell’s nucleus, and are grouped into multiple chromosomes
Chromosomes are only visible when a cell is in the process of dividing
The rest of the time, the DNA + protein threads exist as a diffuse mass called chromatin
Chromosomes
Chromosomes: Found in eukaryotic cells Pass genetic information from one generation
to the next Made up of DNA The cells of every organism have a specific #
of chromosomes EX: Fruit flies= 8 chromosomes, Humans= 46 chromosomes, carrot cells= 18 chromosomes
Each chromosome is composed of two chromatids
Eukaryotic Cell Division
Before dividing, the eukaryotic cell replicates its chromosomes
The two copies of the chromosome are called chromatids, and they are connected to each other at a region called the centromere
The pair of chromatids is still only one chromosome, and the chromatids are not considered chromosomes until they separate from one another
Chromatids
Chromatids: 2 identical strands that make up 1 chromosome During cell division, sister chromatids separate
from each other One chromatid then goes to each of the
2 new cells
The Cell Cycle
The Cell cycle= A series of events that cells go through as the grow and divide Cells grow Prepare for division Divide to form 2 daughter cells Each daughter cell then begins the cycle
again
Events of the Cell Cycle
Events of the cell cycle can be divided into two major stages:1. Interphase= Can be quite long. Divided into 3
parts G1= Cells grow and increase their size;
producing proteins and organelles S= Chromosomes replicate, DNA is synthesized G2= A time of metabolic activity; proteins needed
for cell division are produced
Events of the Cell Cycle
Mitosis Phase (M Phase) Consists of two processes: mitosis and cytokinesis During mitosis, the chromosomes divide and are
distributed into two daughter nuclei During cytokinesis, the cytoplasm is divided into two These two processes result in the production of two
genetically identical daughter cells
Mitosis
Mitosis= Process of cellular division. Divided into 4 phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Prophase
Prophase= longest phase of mitosis (50-60%) of total time required to complete mitosis Chromosomes become visible Centrioles (2 tiny structures located in the cytoplasm)
separate and take opposite sides of nucleus Condensed chromosomes attach to the spindle Each chromosome has two chromatids joined at the
centromere Chromosomes coil more tightly Nuclear envelope breaks down & nucleolus disappears The chromosomes begin moving toward the center of the
cell
Metaphase
Metaphase= Lasts only a few minutes The spindle is fully formed All the centromeres of chromosomes line up in
center of the cell Microtubules connect centromere of each
chromosome to the 2 poles of the spindle
Anaphase
Anaphase- The centromeres of the chromosome come
apart and the sister chromatids split & separate becoming individual chromosomes (called daughter chromosomes)
Chromosomes move into two groups near poles of the spindle
The cell elongates Anaphase ends when chromosomes stop
moving
Telophase
Telophase- (basically the reverse of Prophase) Cell elongation that began in anaphase continues Chromosomes begin to disappear into tangle of
dense material (Chromatin fibers uncoil) Nuclear envelope reforms around each cluster of
chromosomes Spindles break apart and disappear Nucleolus becomes visible in each daughter
nucleus Mitosis is complete
**CELL DIVISION HOWEVER IS NOT COMPLETE**
Cytokinesis
Cytokinesis- Division of the cytoplasm itself and is the final phase of cellular division Usually occurs during the same time as
telophase In animal cells= cytoplasm is drawn inward
and pinched into two equal parts In plant cells= Cell plate forms causing a cell
wall to form between the 2 divided nuclei
Regulating the Cell Cycle
Controls on Cell Division: Cell growth can be turned on and off depending on the situation EX: if cells growing on a Petri dish are
removed, the cells surrounding that now empty space will start dividing, filling in the area where the cells were removed
Uncontrolled Cell Growth
The consequences of uncontrolled cell growth in multicellular organisms can be very severe. Cancer cells DO NOT respond to the signals
that regulate the growth of most cells They divide uncontrollably forming tumors Some fail to respond to internal regulator proteins Some fail to respond to external regulator
proteins Causes of cancer can be: smoking, radiation
exposure, and even some viral infections
The Cell Cycle & Cancer
Cancer is a disease of the cell cycle Systems that control the cell cycle do not
work in cancer cells As a result, cancer cells divide excessively
and can invade other body tissues The excessive growth can result in an
abnormal mass called a tumor
Tumors
Benign tumor-abnormal mass of normal cells; can cause problems if they grow in an organ; remain in their original site; can usually be completely removed by surgery
Malignant tumor-cancerous; capable of spreading to other body areas; displaces normal tissue; can form new tumors by breaking apart and spreading through the circulatory system (called metastasis)
Types of Cancers
Carcinomas-originate in the external or internal coverings of the body (skin)
Sarcomas-originate in tissues that support the body (bone and muscle)
Leukemias and Lymphomas-cancers of blood forming tissues (bone marrow, spleen, and lymph nodes)
Treatments for Cancer
Radiation- parts of the body with cancerous tumors are exposed to high energy radiation, which disrupts cell division (damage to ovaries or testes may cause sterility)
Chemotherapy-administration of drugs that disrupt cell division; some interfere with the formation or functioning of the spindle
Meiosis
Essential for the formation of gametes (ova and sperm) that will be used for sexual reproduction
Occurs in two consecutive cell divisions Reduces the chromosome number by ½ (for
humans, this means creating gametes that have 23 chromosomes)
Meiosis Vocabulary
Chromosomes – the number in each cell is cut in half and are different from each other and the parent cell.
Gametes – are made during meiosis and are specialized cells involved in sexual reproduction.
Tetrad – a structure containing 4 chromatids. (key to Meiosis) Pg. 276
Crossing-over – the exchange of portions chromatids during the pairing up of chromosomes. Pg. 276
Meiosis Vocabulary
Chromosome Number P. 275 Homologous – chromosomes have a
corresponding chromosome from the opposite-sex parent. Ex. Adult fruit fly has 8 chromosomes- 4 from male parent & 4 from female parent
Diploid - “two sets”; a cell that contains both sets of homologous chromosomes & genes. 2(N) Ex. Fruit fly has a diploid number of 8 so 2N=8.
Haploid – “one set”; a cell that contains one set of chromosomes & genes. (N) Ex. N =4
Human Chromosomes
Occur in pairs (there are 23 pairs) in somatic cells (typical body cells); these are called diploid cells (di=2)
Occur unpaired (a single set of 23) in the gametes; these are called haploid cells
The paired chromosomes in somatic cells are called homologous chromosomes, because they have genes for the same traits
Human Chromosomes
22 of the chromosome pairs are called autosomes
The 23rd pair consists of the sex chromosomes
Human females have a pair of sex chromosomes called X chromosomes (XX)
Human males have one X chromosome and one Y chromosome (XY)
Inheritance of Human Chromosomes One chromosome from each pair is inherited
from our mothers, and the other chromosome in the pair is inherited from our fathers
At the time of fertilization, the two haploid gametes (sperm and ovum) unite to form a diploid cell called the zygote
Fertilization results in the formation of a diploid cell, thus restoring the normal diploid number of human chromosomes
Meiosis occurs in reproductive organs
Meiosis I
DNA that is in special cells in the reproductive organs is copied.
The cells divide and 2 cells are formed which are different from each other and the parent cell.
Meiosis I Phases Pg. 276
Interphase I – DNA replication, forming duplicated chromosomes.
Prophase I – Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Metaphase I – Spindle fibers attach to the chromosomes.
Anaphase I – Fibers pull the homologous chromosomes toward opposite ends of the cell.
Telophase I & Cytokinesis – Nuclear membranes form and the cell separates into 2 cells.
Meiosis II
Cells divide again, but DNA is not copied first. 4 daughter cells are produced. Each cell contains half of the number of
chromosomes as the original parent cell.
Meiosis II
Prophase II – Meiosis I results in 2 (N) haploid daughter cells, each with half the number of chromosomes as the original cell.
Metaphase II – Chromosomes line up in a similar way to metaphase stage in mitosis.
Anaphase II – sister chromatids separate & move toward opposite ends of the cell.
Telophase II & Cytokinesis – Meiosis II results in 4 (N) haploid daughter cells.
Comparing Mitosis & Meiosis
Mitosis - 2 cells that are exactly alike & like parent.
Meiosis – 4 cell with each having only half the # of chromosomes as the parent cell and they are genetically different form one another.