chromosomes and cell reproduction chap. 6 section 1
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Chromosomes and Cell Reproduction
Chap. 6
Section 1
Chromosomes – Formation of new Cells by Cell Division
• Cell division occurs in humans & other organisms at different times in their lives
• The type of cell division differs depending on the organism & why the cell is dividing
• Reproduction, growth, development, repair, or asexual reproduction, or formation of gametes
• Gametes – an organism’s reproductive cells- such as sperm or ovum (egg) cells
• All information stored in DNA must be present in each resulting cells
• DNA is first copied – then distributed
• Each cell ends up with a complete set (copy) of DNA
Prokaryotic Cell Reproduction• Prokaryote’s single DNA
molecule is circular & is attached to the inner cell membrane
• Binary fission – a form of asexual reproduction that produces identical offspring
• Occurs in 2 stages – 1st,DNA is copied 2nd, cell divides
Binary fission animation
• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter10/animation_-_cell_division.html
• http://www.classzone.com/books/hs/ca/sc/bio_07/animated_biology/bio_ch05_0149_ab_fission.html
Bacterial Growth
• http://www.ryancshaw.com/Files/micro/Animations/BacterialGrowth/micro_bacterial_growth.swf
Eukaryotic Cell Reproduction• Information
encoded in DNA organized into units called genes
• Gene- a segment of DNA that codes for a protein or RNA molecule
• Genes play an important role in determining how a person’s body develops & functions
• Chromosomes – the DNA & the proteins associated with DNA- are copied and become visible
• Chromatids – the exact copies of DNA that make up each chromosome
• Centromere – point of attachment of the chromatids
• Chromatids become separated during cell division, new cell will have same genetic information as original cell
How Chromosome Number and Structure Affect Development
• Somatic cell – any cell other than sperm or egg cell
• Humans normally has two copies of 23 different chromosomes which differ in size, shape, and set of genes
• Each chromosome contains thousands of genes which determines how you develop & function
Sets of Chromosomes• Homologous
chromosomes-chromosomes that are similar in size, shape, and genetic content
• 23 – from each parent• Diploid- containing two
sets of chromosomes, such as somatic cells
• Haploid- contains one set of chromosomes, such as gametes
• The symbol n is used to represent one set of chromosomes
• Zygote- is a fertilized egg cell, the first cell of a new individual
• Each organism has a characteristic number of chromosomes
• P. 121 Table 1 see chart
Sex Chromosomes• Autosomes-
chromosomes that are not directly involved in determining the sex (gender) of an individual in humans 22 pairs
• Sex chromosomes –contain genes that will determine the sex of the individual
• Often referred to as “X” and “Y” chromosomes
• In humans, a female is XX; while a male is XY
• The structure & number of sex chromosomes vary in different organisms
• Some insects there is no Y chromosome- the female is XX, but the male is XO (O indicates the absence of a chromosome)
• In birds, moths, & butterflies, the male has two X, while female has only one
Change in Chromosome Number• The presence of all 46
chromosomes is essential for normal development & function
• Trisomy- humans with more than two copies of a chromosome, will not develop properly
• Karyotype-a photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size
Make a Karotype
• http://learn.genetics.utah.edu/content/begin/traits/karyotype/
• Trisomy 21(an extra 21 chromosome), also Down syndrome all have similar characteristics
• Mothers younger than 30,1 in 1500 births
• Mothers 37 & older, 1 in 290 births
• Mothers over 45, as high as 1 in 45 births
• As a female ages, her eggs can accumulate an increasing amount of damage
• Disjunction-when sperm and egg cells form, each chromosome & its homologue separate
• Nondisjunction- chromosomes fail to separate-one new gamete ends up with both chromosomes & the other gamete none
• Trisomy occurs when the gamete with both chromosomes fuses with a normal gamete
Prenatal Testing
• Amniocentesis
• Choriconic villi
Change in Chromosome Structure• Mutations- change in
an organism’s chromosome structure
• Deletion- a piece of a chromosome breaks off completely- can be fatal
• Duplication-a chromosome fragment attaches to its homologous chromosome, which will now carry two copies of certain set of genes
• Inversion – the chromosome piece reattaches to the original chromosome but in reverse orientation
• Translocation-a piece reattaches to a nonhomologous chromosome
Homework
• Do section 1 key terms (definitions) 13 words
• Section 1 review p. 124
• Questions 1-5 write the question
The Cell Cyclesection 2
Cell Cycle
• http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP13604
The Life of a Eukaryotic Cell• The Cell Cycle is a
repeating sequence of cellular growth and division during the life of an organism
• Cell usually spends 90% of its time in the first 3 phase of the cycle, which are called interphase
• Last 2 phases of cell cycle will only occur if the cell is about to divide
• First growth (G1) phase-cell grows rapidly- carries out routine functions- some cells stay in this phase
• Synthesis (S) phase- Cell’s DNA is copied-two chromatids attached at the centromere
• Second growth (G2) phase- preparations are made for the nucleus to divide – microtubules are rearranged in preparation for mitosis- repair of DNA mistakes
Cell Cycle Animation
• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html
• Mitosis- process during cell division in which the nucleus of a cell is divided into two nuclei-same number & kinds of chromosomes as original cell
• Cytokinesis- the process during cell division in which the cytoplasm divides
• Cell cycle may be summarized as follows:
G1 - S – G2 - M - C
Cell cycle virtual lab
• http://bio.rutgers.edu/~gb101/lab2_mitosis/index2.html
Control of the Cell Cycle• Cells have a set of
“red light-green light” switches that are regulated by feedback information from the cell
• Cell cycle is controlled by many proteins
• Cell growth (G1) checkpoint- makes the decision of whether the cell will divide
• During S phase, DNA is copied, if conditions not favorable, cells can typically stop the cell cycle
• DNA synthesis (G2) checkpoint - DNA repair enzymes check DNA replication – if okay, mitosis occurs
• Mitosis checkpoint – triggers the exit of mitosis – also signals the beginning of the G1 phase
When Control is Lost: Cancer• Genes contain
information necessary to make proteins
• Proteins control cell growth & development
• Cancer- uncontrolled growth of cells – a disorder of cell division
• Mutations over producing growth-promoting molecules or inactivating the control proteins that act to slow or stop cell cycle
Cancer Map
• http://www.insidecancer.org/
Cancer Biology
• http://www.cancerquest.org/images/Documentary/English/DocInterfaceEng.swf
Homework
• Section 2 review 1-4 page 127
• Section 2 Key terms page125
• Chapter review page 134
2, 7-8,12,14,17
Mitosis & Cytokinesissection 3
• Cells receiving the signal to divide continue past the G2 phase – enter the last 2 phases of the cell cycle-mitosis & cytokinesis
• During mitosis, chromatids are physically moved to opposite sides of the dividing cell with the help of spindles
Forming the Spindle• Spindle-cell structure made
of both centrioles & microtubule fibers that move chromosomes during cell division
• Centrosome – organelle that organizes the assembly of the spindle
• Centrioles & spindle fibers of hollow tubes of protein –microtubules
• Spindle fiber-individual; centrioles- 9 triplets arranged in a circle
• Plants don’t have centrioles
Separation of Chromatids by Attaching Spindle Fibers
• Microtubules attach to the centromeres & poles, the two chromatids can be separated
• Once separated, the chromatids move along paths described by microtubules
• When chromatids are separated, they are called chromosomes
Mitosis & Cytokinesis• Divided into 4 phases:• Step 1 Prophase –
chromosomes coil up & become visible; nuclear envelope dissolves & a spindle fiber forms
• Step 2 Metaphase – chromosomes move to the center of the cell & line up along the equator; spindle fibers link the chromatids of each chromosome to opposite poles
• Step 3 Anaphase – chromatids divide (now called chromosomes) move toward opposite poles as spindle fibers shorten
• Step 4 Telophase – nuclear envelope forms around the chromosomes at each pole; chromosomes begin to uncoil & spindle dissovles & disappear –
• Mitosis complete
Cytokinesis• The cytoplasm divides in
half, cell membrane grows to enclose each cell, forming two separate cells
• Two genetically cells where there was one
• Cells lacking cell walls, the cell is pinched in half by protein threads
• Cells with cell wall - vesicles formed by Golgi apparatus fuse at midline to form cell plate
• Cell wall forms on either side of cell plate• Offspring cells – about equal size; identical copy
of the original chromosomes; & receives about ½ of original cytoplasm & organelles
Homework• Write question
• Section 3 Review page 132 1-4
• Chapter review page 134
1,3-6,9,10,11
STP 1-3
Bonus
Page 129 Calculating the number of cells resulting from Mitosis 1-3 show work
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