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Objectives
1. Define mitosis and meiosis.
2. How do simple somatic cells reproduce?
3. What is the chromosome number of human cells before
and after division? Mitosis and Meiosis?
4. Be able to draw the stages of mitosis and meiosis. (see figure 17.11, from your text)
5. Draw a homologous pair of chromosomes? (see figure 17.9)
6. Be able to recognize the four stages of
mitosis? What is going on during each
phase?
7. What is cytokinesis?
8. Describe the events of meiosis that produce haploid
cells?
9. Compare and contrast meiosis and mitosis? What are the really big differences? (for this one you are on your own, let me know what you
think?)
10. Describe the processes of replication, transcription and translation.
11. Given a short sequence of DNA be able to read it and give the amino acid
sequence that it codes for.
12. Be able to recognize the correct
molecular structure of DNA
13. What is
correct base pairing in DNA
for times sake we
will not be covering the following information. But this is the info I would want you to know if we did. (This will not be on the exam)
14. What effects can mutation have on protein synthesis?
15. How are genes
regulated?
Figures that you should
know. The cell cycle fig 17.1, Mitosis fig 17.9, Meiosis fig 17.11
1. The body will form trillions of cells during your lifetime yet you come from only one cell.
1) Mitosis, which occurs in all cells except the gametes, produces identical new cells with the same chromosome number as the parent cell.
2) Meiosis produces gametes with half the chromosome number as the parent cell.
2. Dividing Cells: the Bridge of Generations
A. This is an overview of cell division Mechanisms.
1) Reproduction, a part of the life cycle of living things, begins with the division of single cells.
2) Each new generation must receive a duplicate of the parent cell’s DNA and enough Cytoplasmic machinery to start up its own operation.
a) DNA contains the genetic instructions for the proteins(are like blueprints), which in turn serve as structural materials and enzymes.
b) The cytoplasm contains the enzymes, organelles, and chemicals necessary to maintain life.
3) Mitosis and meiosis are Eukaryotic nuclear division mechanisms that lead to the distribution of DNA to new nuclei in the new daughter cells, created by the destruction of the old cell.
a) Mitosis is used by multicelled organisms for growth by repeated divisions of somatic cells.
b) Meiosis occurs only in germ cells that divide to form gametes.
B. Key
points about chromosomes
1) Chromosomes are molecules of DNA complexes with proteins: between divisions, the threadlike chromosome mass is referred to as chromatin.
2) Prior to division, each chromosome is duplicated to form two sister chromatids held together by a centromer, which is also the area where the microtubules of the spindle will attach.
C. Mitosis and the Chromosome Number.
1) All somatic cells of a particular species have the same number of chromosomes: example: humans have 46.
a) Chromosome comes in pairs—one member from each parent.
b) Chromosome pairs that carry genes for the same traits are called homologous chromosomes.
2) Chromosome number (n) tells how many of each type of chromosome is present in a cell: 2n is diploid (two sets of chromosomes); n is haploid (only one set).
3) During growth and development, mitosis maintains the chromosome number of somatic cells in the species.
2. The not so quiet part of the Cell Cycle
1) During Interphase the cell’s mass increases (G1), the DNA is doubled (S) and the Cytoplasmic components approximately double in number (G2)
2) Some cells are arrested in Interphase and never divide again (example: brain cells)
3. A tour of the 4 Stages of Mitosis
1) Chromosomes start condensing to become visible as rodlike units, each consisting of two sister chromatids joined at the centromer: each chromatid bears a kinetochore which severs as an attachment site to the microtubules of the spindle.
2) The spindle starts forming from reassembled microtubules of the cytoskeleton.
3) The spindle separates the centrioles to opposite poles of the cell.
B. Transition
to Metaphase
1) The nuclear membrane breaks apart.
2) Microtubules of the spindle interact with the chromosomes to orient the sister chromatids toward opposite poles.
3) All chromosomes become aligned at the cell’s equator, halfway between the poles.
C. Anaphase
1) Sister chromatids separate and move toward opposite poles.
a) The microtubules attached to the kinetochore shorten, pulling the chromosomes to the poles
b) The spindle elongates pushing the poles further apart.
2) Now each chromatid is an independent chromosome
D. Telophase
1) Telophase begins when chromosomes arrive at the poles
2) The chromosomes no longer attached to the microtubules decondense
3) The nuclear envelope forms form the fusion of small vesicles: mitosis is complete
4) In mitosis, each new cell has the same chromosome number as the parent nucleus.
6. Overview of Meiosis
1) Meiosis is reductional division that occurs in the nucleus of a dividing germ cell in the ovaries of testes.
a) Meiosis begins with diploid (2n=46) spermatogonia or oogonia and produces haploid gametes (n=23)
b) Meiosis produces gametes that have one of each pair of homologous chromosomes
2) Meiosis begins with the duplication of chromosomes in Interphase but then leads to meiosis I, which produces tow haploid cells with duplicated chromosomes and meiosis II four cells with unduplicated chromosomes.
B. Two
divisions, Not One
1) During meiosis I, the homologous chromosomes first pair up, then separate form one another; (at this point effectively producing haploid cells) eventually the cytoplasm divides to produce two cells.
a) each of the two daughter cells receives a haploid number of chromosomes
b) Each chromosome is still duplicated
2) In meiosis II, the sister chromatids of each chromosome separate; the cytoplasm divides again, resulting in four haploid cells.
7. A Visual tour of the stages of Meiosis (see fig on meiosis I and II)
8. Key events during Meiosis I
1) Homologous chromosomes pair up in a process called synopsis, to form a tetrad.
a) Nonsister chromatids exchange segments in a process called crossing over
b) Because alleles for the same trait can vary, genetic recombination’s in each chromosome can result; this is one source of genetic variation
2) After crossing over, the Nonsister chromatids begin to partially separate but remain attached by chiasmata.
B. Metaphase I alignments
1) During metaphase I, homologous chromosomes (tetrads) randomly line up at the spindle equator
2) During anaphase I, homologous chromosome (still duplicated, dyads) separate into two haploid cells, each of which has a random mix of maternal and paternal chromosomes.
3) Variation at fertilization is form three sources;
a) crossing over occurs during prophase I.
b) Random alignments at metaphase e I lead to millions of combinations of material and paternal chromosomes in each gamete
c) Of all the genetically diverse gametes produced, chance will determine which two will meet.
4) After cytokinesis, there is a brief interkinesis but DNA is not duplicated.
9. Meiosis and the Life cycle
1) In males, meiosis and gamete formation are called spermatogenesis
a) germ cell (2n)à primary spermatocyte (2n)--?Meiosis Ià two secondary spermatocytes (n)à Meiosis IIà four spermatids (n)
b) Spermatids change in form ; each develops a tail to become mature sperm.
2) In females, meiosis and gamete formation are called oogenesis
a) germ cell (2n)à primary oocyte (2n)à Meiosis I à secondary oocyte (n and large in size) plus polar body (n, and small in size)à MeiosisIIà one large ovum (n) plus three polar bodies (n, small)
b) the single ovum is the only cell capable of being fertilized by a sperm: the polar bodies wither and die.
10. Meiosis and Mitosis compared
Possible questions:
1) Follow a single chromosome through the process of mitosis. What is the significance of the result?
2) Follow a single chromosome through the process of meiosis. What is the significance of the result?
3) Be able to diagram a mitotic and meiotic cell division
Possible multiple choice questions:
1) You are working in a scientists laboratory, and she gives you a cell, It contains 23 chromosomes. She asks you why that is so you would give the following answer.
a) Yuck this is a cell form a dead person?
b) Yuck this is a sperm?
c) This cell has undergone Meiosis and now contains half the number of human chromosomes
d) This cell has undergone Mitosis and now contains half the number of human chromosomes
e) This cell has undergone Meiosis and contains double the number of human chromosomes.
2) In order for a cell to divide and for each new cell to live it must minimally have
a) its own credit card and cell phone
b) cytoplasm and genes
c) a duplicate of the parents cell’s DNA and enough cytoplasmic machinery to start up its own operation
d) only cytoplasm and mitochondria
e) half of the genes
3) You have learned a number of facts about chromosomes in this class. Which of the following are true?
a) chromosomes contain your genes
b) humans have 46 chromosomes, a set of 23 maternal and 23 paternal chromosomes
c) chromosomes are physically made up of DNA and associated proteins
d) Only females have chromosomes
e) During most of the life of a typical cell, the chromosomes are unwound and diffuse within the nucleus and called chromatin.
4) the cell cycle is
a) a lot like a unicycle only smaller
b) the events that occur in a cells life from when it is created to when it divides
c) mostly Interphase
d) mostly doubling of DNA
e) only occurs once in most tissues like the skin, brain and muscle
5) Mitosis consists of which of the following stages?
a) prophase
b) metaphase
c) anaphase
d) telophase
e) astrophase
Answers: 1) b,c 2) c 3) a,b,c,e 4) b,c 5) a,b,c,d
Objectives:
1. Understand how the instructions for producing heritable traits are encoded in DNA.
2. Know the parts of a nucleotide and know how they are linked together to make DNA.
3. Understand how DNA is replicated and what materials are needed for replication.
4. Be able to visualize the organization of DNA in chromosomes.
5. Know how the structure and behavior of DNA determine the structure and behavior of the forms of RNA during transcription.
6. Know who the structure and behavior of the three forms of RNA determine the primary structure of polypeptide chains during translation.
7. Know the various ways that gene activity (replication and transcription) are turned on (activated) and Off (inactivated).
1. Two scientist Watson and Crick discovered the structure of DNA using cardboard atoms and bent wire bonds and data gleaned from other researchers like Linaus Pauling.
2. DNA structure and replication
1) It is composed of four kinds of nucleotides, each of which consists of:
a) a five carbon sugar (deoxyribose)
b) a phosphate group
c) one of four bases—adenine (A), guanine (G) thymine (T) Cytosine (C)
2) Watson and Crick used numerous sources of data to build models of DNA
a) DNA exists as a long, thin molecule of uniform diameter (2 nano meters or 0.000000002 meters)
b) Nucleotides are joined along the molecule’s length: sugar-phosphate linkages to form a molecule “backbone.”
c) DNA consists of two strands of nucleotides twisted into a double helix
d) Base pairs are formed by the hydrogen bonding of A with T and G with C thus A=T and G=C.
3) A gene is a region of a DNA molecule that codes for the assembly of amino acids into a single polypeptide chain.
B. DNA replication (occurs before mitosis and meiosis)
1) DNA is duplicated before a cell divides.
a) first, the two stands of DNA unwind and expose their bases to serve as a template.
b) Then, unattached nucleotides are linked by hydrogen bonds to exposed bases according to base pairing rules.
c) Thus replication results in DNA molecules that consist of one “old” strand and one new strand this process is called semiconservative replication.
2) DNA polymerases assemble the nucleotides into nucleic acids.
C. DNA repair
1) DNA polymerases, DNA ligases, and other enzymes engage in DNA repair
2) If the sequence of bases becomes altered, the enzymes read the complementary sequence on the other strand and restore it. Sometimes the wrong strand is repaired and a mutation occurs.
3. Organization of DNA in Chromosomes
1) Some histones (a type of protein) act as spools to wind the DNA into units called nucleosomes
2) Another histone stabilizes the arrangement and allows the beaded chain to form looped regions.
4. Protein Synthesis
1) In transcription, molecules of RNA are produced on the DNA templates in the nucleus.
2) In translation, RNA molecules are shipped form the nucleus to the cytoplasm to be used in polypeptide assembly.
B. RNA differs form DNA
1) RNA is single stranded
2) It contains the sugar ribose
3) The base uracil substitutes for the thymine of DNA
1) Ribosomal RNA (rRNA) combines with proteins to form ribosome’s upon which polypeptides are assembled.
2) Messenger RNA (mRNA) carries the blueprint to the ribosome
3) Transfer RNA (tRNA) brings the correct amino acid to the ribosome and pairs up with an mRNA code for that amino acid.
5. Transcription of DNA into RNA
1) Only one region of one DNA strand is used as a template
2) RNA polymerase is used instead of DNA polymerase
3) The result of transcription is a single stranded RNA
1. The introns (noncoding portions) are removed before the transcript leaves the nucleus.
2. Only the exons (portions that will eventually be translated) remain in the finished transcript that leaves the nucleus.
6. From mRNA to Proteins (Translation)
1) Both DNA and its mRNA transcript are linear sequences of nucleotides carrying the hereditary code.
2) Three bases ( a triplet) specify an amino acid to be included into a growing polypeptide chain.
a) The genetic code consists of sixty one triplets that specify amino acids and three that serve to stop protein synthesis.
b) Each base triplet in RNA is called a codon.
c) Most amino acids can be specified by more than one codon.
B. Toles of tRNA and rRNA
1. Each kind of tRNA has an anticodon that is complementary to an mRNA codon: each tRNA also carries one specific amino acid.
2. After the mRNA arrives into the cytoplasm, a specific anticodon on a tRNA bonds to the codon on the mRNA by complementary base-pairing, and thus a correct amino acid is brought into place.
3. Translation occurs on the surface of ribosome’s (rRNA + proteins) composed of two subunits that unite during translation.
7. Stages of Translation
A. In initiation, a complex forms in this sequence: initiator tRNA + small ribosomal subunit + mRNA + large ribosomal subunit.
8. Effects of mutation on protein synthesis
A. A gene mutation is a change in one to several bases in the nucleotide sequence of DNA.
1) small scale changes such as bases added, deleted or replaced are called point mutations.
a) mutations in germ cells, but not somatic cells can be passed on to offspring.
b) Mutagens such as viruses, ultraviolet radiation, chemicals and free radicals can change the structure of DNA
2) some mutations occur spontaneously due to replication errors.
a) Sickle cell anemia is the result of a base pair substitution.
b) A frameshift mutation is the result of one or more base pairs being added or deleted form the DNA.
9. Regulating Gene Action
A. Because all cells in your body have the same genetic instructions, only a relatively small number of genes are active at any given time in any given tissue (ex: only red blood cells activate hemoglobin genes)
1) A gene may have a DNA sequence that does not code for protein synthesis but instead interacts with a regulatory protein.
2) For example when the body temperature rises, a regulatory protein called heat shock factor binds to a portion of the gene that turns on transcription that leads to translation of repair proteins.
C) Hormones as control agents.
1) most body cells have receptors for somatotropin, which controls growth processes.
2) Prolactin affects only cells of the mammary glands and only after delivery of offspring.
Multiple choice questions.
1. The four nucleotides that make up DNA are
a) guanine
b) adenine
c) uracil
d) thymine
e) cytosine
2. Which of the following represents a correct base pairing of DNA
a) A=C
b) A=T
c) A=G
d) T=C
e) T=G
3. Which of the following are ways in which a strand of RNA differs from a strand of DNA
a) RNA is single stranded and DNA is double stranded
b) RNA contains the sugar ribose in its nucleotides and DNA contains an alternate form of the sugar Deoxyribose
c) RNA contains uracil and DNA contains Thymine
d) RNA and DNA do not differ appreciably
e) RNA is an exact copy of DNA
4. Human genes contain stretches of DNA that code for pieces of a protein and stretches that do not code for a protein. It is thought that the stretches that eventually become a protein are like cassettes that code for a functional portion of the protein. Rather than having evolution make an entire protein from scratch the cassettes are moved around until a conformation is reached that will perform a specific function. These cassettes are coded for by the
a) introns
b) exons
c) telomers
d) histones
e) nucleotides
5. Which of the following would represent a frameshift mutation, which are the most devastating types of mutations to the structure of a protein. See nan run far now
a) See jan run far now
b) Sen anr unf arn ow
c) See run far now
d) See run jan far now
Answers 1) a,b,d,e 2) b 3) a,b,c 4) b 5)b
The following is a list of websites that I found helpful.
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The virtural genome center has information on databases and ways to look at your DNA http://alces.med.umn.edu/VGC.html |
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http://dir.niehs.nih.gov/dirlmg/repl.html interesting directory of DNA pictures and DNA replication information |