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