8.1 Why Do Cells Divide? - Gavilan Collegehhh.gavilan.edu/jcrocker/documents/Ch08-11Review_000.pdf · 8.1 Why Do Cells Divide? Cell division is required for growth and development.
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Describe the structure of DNA. Be sure to include what forms the skeleton and how are the strands held together?
2.
Compare and contrast chromosomes, chromatids, genes, and alleles.3.
Compare and contrast prokaryotic and eukaryotic cell division.4.
Describe the process of asexual reproduction in eukaryotic cells. (DNA replication and mitosis)5.
Compare and contrast animal and plant cell asexual reproduction.
(mitosis)6.
Compare and contrast mitosis and meiosis.7.
Without genetic testing how could you determine if an organism is homozygous or heterozygous for a specific trait (ie
hair color)?8.
Describe three ways that genetic variability is increased.9.
Two fruitflies
are bred. One is true breeding for red eyes and one is true breeding for white eyes. Red eyes are dominant. What will the genotype and phenotype of the offspring be?
10.If two of the offspring of the above match are crossbred what will the genotype and phenotype of their offspring be?
11.In the above examples how would the genotypes and phenotypes be different if red eye color was partially dominant producing pink eyes when heterozygous?
12.In the example above (#9) the red-eyed fruitfly
has straight wings and the white-eyed fruitfly
has wrinkled wings. Straight wings are dominant. What would the genotype and phenotype of the offspring be?
13.What characteristics can make genetic disorders more likely to be passed from one generation to the next? (at least 3)
14.Describe the process of DNA replication. What is meant by semiconservative
replication? How are continuous synthesis and discontinuous synthesis involved in the
process?15.How common are mistakes in replication? What safeguards are in place to prevent mistakes?
What types of mistakes are relatively common?16.Compare and contrast DNA and RNA.17.Describe the process of transcription.18.Describe the process of translation.19.What are codons
and how do they function in protein synthesis?20.Describe the ways by which gene expression may be regulated.
Reproduction in which offspring are formed from a single parent, without having a sperm fertilize an egg, is called asexual reproduction.• Asexual reproduction produces offspring that
are genetically identical to the parent.• Examples of asexual reproduction occur in
Duplicated chromosomes separate during cell division.• Prior to cell division, the DNA within each
chromosome is replicated.• The duplicated chromosomes then consist of two
DNA double helixes and associated proteins that are attached to each other at the centromere. Each of the duplicated chromosomes attached at the centromere
is called a sister chromatid.• During mitotic cell division, the sister chromatids
separate and each becomes a separate chromosome that is delivered to one of the two resulting daughter cells.
The ovaries and testes undergo a special kind of cell division, called meiotic cell division, to produce gametes (eggs and sperm).• Gametes contain only one member of each pair of
autosomes, plus one of the two sex chromosomes.
• Cells with half the number of each type of chromosome are called haploid cells.
• Fusion of two haploid cells at fertilization produces a diploid cell with the full complement of chromosomes.
cells: mitotic cell division and meiotic cell division.• Mitotic cell division may be thought of as
ordinary cell division, such as occurs during development from a fertilized egg, during asexual reproduction, and in skin, liver, and the digestive tract every day.
• Meiotic cell division is a specialized type of cell division required for sexual reproduction.
Anaphase Sisterchromatids separate and move to opposite poles of the cell; spindle microtubules that are not attached to the chromosomes push the poles apart.
Telophase One set ofchromosomes reaches each pole and relaxes into the extended state; nuclear envelopes start to form around each set; spindle microtubles begin to disappear.
CytokinesisThe cell divides in two; each daughter cell receives one nucleus and about half of the cytoplasm.
Interphase of daughter cells Spindlesdisappear, intact nuclear envelopes form, chromosomes extend completely, and the nucleolus reappears.
unattached spindle microtubules
(e) (f) (g) (h)
8.5 How Does Mitotic Cell Division Produce Genetically Identical Daughter Cells?
8.6 How Does Meiotic Cell Division Produce Haploid Cells?
Fig. 8-12a–d
paired homologous chromosomes
recombined chromatids
spindle microtubule
kinetochoreschiasma
(a) (b) (c) (d)Prophase I Duplicated chromosomes condense. Homologous chromosomes pair up and chiasmata occur as chromatids of homologues exchange parts by crossing over. The nuclear envelope disintegrates, and spindle microtubules form.
Metaphase IPaired homologous chromosomes line up along the equator of the cell. One homologue of each pair faces each pole of the cell and attaches to the spindle microtubules via the kinetochore (blue).
Anaphase IHomologues separate, one member of each pair going to each pole of the cell. Sister chromatids do not separate.
Telophase ISpindle microtubules disappear. Two clusters of chromosomes have formed, each containing one member of each pair of homologues. The daughter nuclei are therefore haploid. Cytokinesis commonly occurs at this stage. There is little or no interphase between meiosis I and meiosis II.
(e) (f) (g) (h) (i)Prophase IIIf the chromosomes have relaxed after telophase I, they recondense. Spindle microtubules re-form and attach to the sister chromatids.
Metaphase IIThe chromosomes line up along the equator, with sister chromatids of each chromosome attached to spindle microtubules that lead to opposite poles.
Anaphase IIThe chromatids separate into independent daughter chromosomes, one former chromatid moving toward each pole.
Telophase IIThe chromosomes finish moving to opposite poles. Nuclear envelopes re-form, and the chromosomes become extended again (not shown here).
Four haploid cellsCytokinesis results in four haploid cells, each containing one member of each pair of homologous chromosomes (shown here in the condensed state).
8.6 How Does Meiotic Cell Division Produce Haploid Cells?
An organism’s two alleles may be the same or different (continued).• If both homologous chromosomes have the
same allele at a locus, the organism is said to be homozygous.
• If two homologous chromosomes have different alleles at a locus, the organism is heterozygous at that locus.
• The gametes of a homozygous individual are all the same at a particular locus, while gametes of a heterozygous individual would contain half one allele and half the other allele.
This allows us to develop a five-part hypothesis to explain the inheritance of single traits.
1.
Each trait is determined by pairs of distinct physical units called genes.
• There are two alleles for each gene, one on each homologous chromosome.
2.
When two different alleles are present in an organism, the dominant allele may mask the expression of the recessive allele; but the recessive allele is still present.
3.
The two alleles of a gene segregate (separate) from one another during meiosis (Mendel’s law of segregation).
Which allele ends up in any given gamete is determined by chance.
5.
True-breeding (homozygous) organisms have two copies of the same allele for a given gene; hybrid (heterozygous) organisms have two different alleles for a given gene.
Mendel predicted the outcome of cross-fertilizing Pp plants with homozygous recessive plants (pp)—there should be equal numbers of Pp (purple) and pp (white) offspring.
Mendel next crossed pea plants that differed in two traits, such as seed color (yellow or green) and seed shape (smooth or wrinkled).• He knew from previous crosses that smooth
and yellow were both dominant traits in peas.• His first cross was a true-breeding plant with
smooth, yellow seeds (SSYY) to a true- breeding plant with wrinkled, green seeds
9.8 Do Mendelian Rules Of Inheritance Apply To All Traits?
When a heterozygous phenotype is intermediate between the two homozygous phenotypes, the pattern of inheritance is called incomplete dominance.• Human hair texture is influenced by a gene
with two incompletely dominant alleles, C1 and C2 .
• A person with two copies of the C1 allele has curly hair; two copies of the C2 allele produces straight hair; heterozygotes
Nucleotide rungs only result in specific pair combinations.• Adenine only pairs with Thymine.• Guanine only pairs with Cytosine.• This A–T and G–C coupling is called
Cells reproduce themselves by making two daughter cells from each parental cell, each with a complete copy of all the parental cell’s genetic information.
During cell reproduction, the parental cell synthesizes two exact copies of its DNA through a process called DNA replication.
DNA replication produces two DNA double helices, each with one original strand and one new strand (continued).• The first step involves enzymes called DNA helicases,
which pull apart the parental DNA double helix.• Next, enzymes called DNA polymerases move along
each separated parental DNA strand, matching each base on the strand with free nucleotides.
DNA replication keeps, or conserves, one parental DNA strand and produces one new daughter strand (semiconservative
DNA polymerase synthesizes new DNA strands.• At the replication forks, DNA polymerase
recognizes unpaired nucleotide bases in the parental strand and matches them up with free nucleotides.
• It then links up the phosphate of the incoming nucleotide with the sugar of the previously added nucleotide, thereby contributing to the growing molecule backbone.
The genetic code translates the sequence of bases in nucleic acids into the sequence of amino acids in proteins.• A sequence of three bases codes for an
amino acid; the triplet is called a codon.• There are 64 possible combinations of
codons, which is more than enough to code for the 20 amino acids in proteins.
11.4 How Is The Information In A Gene Transcribed Into RNA?
Transcription begins when RNA polymerase binds to the promotor
of a gene.
• RNA polymerase catalyzes the transcription of DNA to RNA.
• RNA polymerase first finds the promoter region (a non-transcribed sequence of DNA bases) that marks the start of a gene, and then binds to it, opening up the DNA as it does.
• Transcription of the gene begins after the promoter is bound to RNA polymerase.
11.5 How Is The Information In Messenger RNA Translated Into Protein?
mRNA, with a specific base sequence, is used during translation to direct the synthesis of a protein with the amino acid sequence encoded by the mRNA.• Decoding the base sequence of mRNA is the
job of tRNA
and ribosomes
in the cytoplasm.• The ability of tRNA
to deliver the correct
amino acid to the ribosomes
depends on base pairing between each codon
of mRNA and a
set of three complementary bases in tRNA, called the anticodon.
11.5 How Is The Information In Messenger RNA Translated Into Protein?
Elongation
Fig. 11-5(4,5,6)
peptide bond
initiator tRNA detaches
catalytic site
ribosome moves one codon to the rightThe second codon of mRNA
(GUU) base-pairs with the anticodon (CAA) of a second tRNA carrying the amino acid valine (val). This tRNA binds to the second tRNA site on the large subunit.
The “empty” tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty.
The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine and valine. The two amino acids are now attached to the tRNA in the second binding site.
11.5 How Is The Information In Messenger RNA Translated Into Protein?
Elongation (continued)
Fig. 11-5(7,8)
The catalytic site forms a peptide bond between valine and histidine, leaving the peptide attached to the tRNA in the second binding site. The tRNA in the first site leaves, and the ribosome moves one codon over on the mRNA.
The third codon of mRNA (CAU) base-pairs with the anticodon (GUA) of a tRNA carrying the amino acid histidine (his). This tRNA enters the second tRNA binding site on the large subunit.
All of the genes in the human genome are present in each body cell, but individual cells express only a small fraction of them.• The particular set of genes that is expressed
depends on the type of cell and the needs of the organism.
• This regulation of gene expression is crucial for proper functioning of individual cells and entire organisms.
Gene expression differs from cell to cell and over time.• The set of genes that are expressed depends
on the function of a particular cell.• Hair cells synthesize the protein keratin, while
muscle cells make the proteins actin
and myosin but do not make keratin.
• A human male does not express a casein gene, the protein in human milk, but will pass on the gene for casein synthesis to his daughter, who will express it if she bears children.
Regulatory proteins that bind to promoters alter the transcription of genes.• Many steroid hormones act in this way.• In birds, estrogen enters cells of the female
reproductive system and binds to a receptor protein during the breeding season.
• The estrogen–receptor combination then binds to the DNA in a region near the promotor
Some regions of chromosomes are condensed and not normally transcribed.• Certain parts of eukaryotic chromosomes are
in a highly condensed, compact state in which most of the DNA is inaccessible to RNA polymerase.
• Some of these tightly condensed regions may contain genes that are not currently being transcribed, but when those genes are needed, the portion of the chromosome containing those genes becomes “decondensed” so that transcription can occur.
Entire chromosomes may be inactivated and not transcribed.• In some cases, almost an entire chromosome
may be condensed, making it largely inaccessible to RNA polymerase.
• In human females, one of their two X chromosomes may become inactivated by a special coating of RNA called Xist, which condenses the chromosome and prevents gene transcription.