Role of DNA
1. Info. In DNA must be present in each cell after division
2. Stores info for which proteins to make and when
3. Directs cell activities 4. DNA gets copied and
redistributed during division
Role of DNA
A single chromosome contains thousands of genes that code for proteins involved in determining how a person’s body develops and function
Pro vs. Eu
How many chromosomes do we have?
1. What is the main difference between Prokaryotic and Eukaryotic organisms?
2. How does cell reproduction occur in prokaryotic organisms?
3. Where does cell reproduction occur in
eukaryotic organisms?
Chromo-somes
1. Each human somatic (body) cell has 23 pairs of chromosomes ( = 46 total chromosomes)
Chromosomes differ in size, shape
Contain thousands of genes that determine how the body functions and develops
Chromo-somes
2. Homologous chromosomes- Each 23 pairs of chromosomes consists of 2 homologues
Similar in size, shape and genetic content (chromatids that are connected)
Chromo-somes
3. One half of each chromosome pair comes from the mother and the other half from the father
Chromo-somes
A somatic cell, that contains 2 sets of chromosomes is diploid
Gametes (sex cells) only have 1 set of chromosomes - haploid
Zygote - a fertilized egg cell We use the symbol “n” to
represent one set of chromosomes
Chromosome numbers in common species
Haploid and Diploid Chromosome Numbers
Autosomes 22 of the chromosome pairs in humans are called autosomes - not directly involved in determining the gender of an individual
Sex Chromosomes
One of the chromosome pairs containing genes that determine the sex of the individual• X and Y• XX - female• XY- male
• The sex is determined by the male
Changes in chromo-some number
1. Presence of all 46 chromosomes is essential for normal development and function
2. Humans missing one chromosome typically do not survive
Changes in chromo-some number
Can detect this in Karyotype
3. More than two copies of a chromosome - trisomy (improper development occurs)
Ex: Down Syndrome (21)
Non-disjunction
When chromosomes don’t separate properly when egg and sperm form
One gamete ends up with both chromosomes, the other has none
Trisomy results when abnormal gamete fuses with another
How many chromosomes do humans have? How many pairs?
What is the difference between “haploid” and “diploid”?
Give the sex chromosomes for females & males
Why is it essential to have all 46 chromosomes?
Draw a pair of homologues, draw a gene on one of the homologues, and label the chromatids
Change in chromo-some structure
MUTATION - change in chromosome structure (4 TYPES)
Change in chromo-some structure
1. Deletion- piece of chromosome completely breaks off (often fatal)
Change in chromo-some structure
2. Duplication- chromosome fragment attaches to its homologue (doubles the info - 2 copies of a gene)
Change in chromo-some structure
3. Inversion- chromosome piece reattaches to original chromosome in reverse orientation
Change in chromosome structure
4. Translocation- chromosome piece attaches to non-homologous chromosome
All of the four mutations discussed could prove fatal for
the individual
Cell Cycle Repeating sequence of growth and division in the life of an organism
Cell Cycle A cell spends 90% of its time in the first three phases – called Interphase• G1• S• G2
Cell Cycle G1- First Growth Phase• Rapid cell growth and
development, routine functions• Major part of cell life spent here• Non-dividing cells remain here• Muscle cells and nerve cells
always here, cannot be replaced
Cell Cycle S- Synthesis phase• DNA copied, end up with sister
chromatid
Cell Cycle G2- Second Growth Phase• Cell prepares nucleus to divide• Microtubules assembled for
moving chromosomes during mitosis
Cell Cycle Mitosis- nucleus divides into two• Each nucleus ends up with
same type and number of chromosomes
• Allows organisms to: Grow Replace damaged tissue Asexually reproduce
Cell Cycle Cytokinesis- cytoplasm divides in half
Control of the cell cycle
1. Cell growth checkpoint (G1) decides whether the cell will divide• A. Cell must be healthy and
large enough first• B. Proteins will stimulate
transition to S phase
Control of the cell cycle
1. Cell growth checkpoint (G1) decides whether the cell will divide• C. If conditions are unfavorable
or cells need a rest, growth will stop here
• D. Nerve and muscle cells remain here forever
Control of the cell cycle
2. DNA synthesis G2 checkpoint- DNA repair enzymes check the DNA replication• A. Once past this point,
proteins trigger mitosis
Control of the cell cycle
3. Mitosis checkpoint- triggers end of mitosis• Signals beginning or G1 phase
again
Losing Control of the cell cycle
Cancer- uncontrolled growth of cells caused by:• A. Mutagens- readily damage DNA
(pollutants, radiation, other environmental factors)
• B. When gene coding for proteins that regulate cell cycle are mutated
Losing Control of the cell cycle
Cancer- uncontrolled growth of cells caused by:• C. When growth promoting
proteins are mutated and actually speed up the rate of cancer Oncogenes- accelerate rate of cell
division
Losing Control of the cell cycle
Cancer- uncontrolled growth of cells caused by:• D. When mutations inactivate the
control proteins that normally slow/stop cell cycle Tumor Suppressor Genes- releases the
“brakes” on cell division
Differentiate between the G1, G2 and S phases of the eukaryotic cell cycle
Relate what occurs at each of the three principal checkpoints in the cell cycle
Why are individual chromosomes more difficult to see during interphase than during mitosis?
Mitosis: Spindles
Made of centrioles and microtubule fibers that move chromosomes during cell division• A. Extra set made right before
division• B. Travel to opposite ends of cell• C. Only animal cells have centrioles• D. Animals and plant cells both have
spindle fibers
Mitosis: Spindles
E. Microtubules attach to cell poles and chromosome centromeres
F. Chromosomes begin to move towards opposite ends of cell
G. Spindle fibers reel in the attached chromosomes as the ends of the fibers at the poles are broken down
H. Each pole gets a full set of chromosomes
46 X’s 92 X’s 46 X’s
46 X’s
46 X’s
46 X’s
Fertilized Cell
Chromosomes copied
Mitosis: Stages
1. PROPHASE• Chromosomes uncoil, become visible• Nuclear envelope disappears• Spindle forms
Mitosis: Stages
2. METAPHASE• Chromosomes move to center of cell
and attach to spindle fibers along equator
Mitosis: Stages
3. ANAPHASE• Centromeres divide• Sister chromatids split and move to
opposite poles as spindle fibers shorten
Mitosis: Stages
4. TELOPHASE• Nuclear envelope reforms• Chromosomes recoil• Spindle and fibers break down
Mitosis: Stages
5. CYTOKINESIS• Cytoplasm divided in half, cell
membrane reforms• Animal: cell pinches in half by belt of
protein• Plant: vesicles from golgi line down
middle of cell to make a cell plate New cell wall grows on either side of
plate Plate breaks cell into two
Mitosis: An Interactive Animation
Molecular Expressions Cell Biology: Mitosis Interactive Java Tutorial
Home(page) Movies - QT and Flash to illustrat...
Dr Chromo's school: mitosis Molecular Expressions Photo Gallery:
Mitosis Mitosis The Cell Cycle & Mitosis Tutorial Mitosis: An Interactive Animation
Describe the function of the microtubules during anaphase
Describe the events that occur during each of the four stages of mitosis
Compare how cytokinesis occurs in plant cells and how it occurs in animal cells