Exam 3 Study Guide BSC 197: Test on 11-6-15
Here is the study guide I have prepared for exam 3 in BSC 197. It consists of three main parts: Cell Cycle, Cell Processes, and Genetics. Best of luck on exam 3!
Like with exam 2, I will release another study guide consisting of the material discussed at the review session.
EXAM 3 STUDY GUIDE: BSC 197 1
Mitosis and Cell Cycle
Multicellular organisms must divide to grow and repair. Fertilized egg cells also depend on cell division to grow. Cell division typically results in the formation of two identical daughter cells, however, sex cells dividing produces non-identical daughter cells. • Genome: the DNA material in a cell
• Chromosome Vocabulary
Don't forget about the age old question of What are the four types of sensory axons?
• Metacentric: centrosome is near center of chromosome
• Submetacentric: centrosome is between center and end of the chromosome • Acrocentric: centrosome is near telomere of chromosome If you want to learn more check out What is the precursor protein to up3 and dag?
• Telocentric: centrosome is at telomere of chromosome
• Telomere: end of a chromosome
• Centrosome: the small pinched region of a chromosome (typically shown metacentric in diagrams, however, that is not always the case)
• Somatic cells: most common, non-reproductive, 2 sets of chromosomes • Gametes: typically referred to as sex cells, half as many chromosomes as somatic cells, produced by meiosis, EX: sperm, eggs
• The majority of the cell cycle is completed in Interphase
• G1 phase: acts as a rest break for the cell
• S phase: DNA synthesis
• G2 phase: acts as a rest break for the cell
• Mitotic (M) phase
• 1) Prophase: replicated chromosomes become thicker and shorten;
centrosomes begin to move outwards
• 2) Prometaphase: spindles extend from centrosomes, chromosomes continue to thicken, spindles bind to the kinetochore of the centromere
• 3) Metaphase: chromosomes line up along midline of the cell If you want to learn more check out What is the first neurotransmitter identified?
• 4) Anaphase: centromere splits, spindles pull chromosomes apart to form sister chromatids
• 5) Telophase: chromosomes are pulled to opposite sides of the cell
EXAM 3 STUDY GUIDE: BSC 197 2
• Cytokinesis: cell divides to form two identical daughter cells, new cell membrane for each daughter cell forms If you want to learn more check out Where did rudy ray moore bear?
• During cytokinesis in plant cells, a cell plate would form Don't forget about the age old question of What is the collection of elements or objects that possess the information the
researcher seeks and about which the researcher will make inferences?
Cancer and the Cell Cycle
Cancer results from a mutation in the cells. If the mutation is not caught by the nucleus, the cell will continue to produce mutated cells eventually leading to the formation of cancer. Meiosis If you want to learn more check out What are the claimed effects of stigma?
• Genetics: scientific study of heredity and variation
• Heredity: the passing down of traits from generation to generation
• Variation: the differences between offspring and their biological parents • Genes: small units of heredity, constructed of DNA
• Locus: a gene’s specific location on a chromosome
• Asexual Reproduction: one parent produces and identical offspring by mitosis • Sexual Reproduction: two parents produce offspring with a mix of trials from each parent • Clone: an offspring identical to its parent
• Sex chromosomes: X and Y, XX = female, XY = male
• Autosomes: chromosomes that do not determine gender (22 in total)
• Diploid cell: a cell with two sets of chromosomes
• Haploid cell: a cell with one set of chromosomes
• Fertilization: a sperm and an egg cell joining together
• Zygote: a fertilized egg cell, produces somatic cells to grow into a fully formed human • Crossing Over: direct exchange of DNA
• Random Fertilization: there are trillions of possible combinations for a sperm and egg Meiosis Process (follows the replication of chromosomes in Interphase)
• chromosomes condense
• chromosomes pair up (synapsis)
• non-sister chromatids exchange DNA material (crossing over)
• groups of 4 chromatids form (tetrads)
• tetrads line up along metaphase plate
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• microtubules from one pole attach themselves to a kinetochore of one chromosome in each tetrad
• microtubules from the other pole attach themselves to the other chromosome of the tetrad
• homologous chromosome pairs separate
• one chromosome moves toward each pole
Telophase I and Cytokinesis
• cell splits to form two haploid daughter cells
• spindle forms
• chromosomes move towards metaphase plate
• kinetochores of sister chromatids attach to microtubules that extend from opposite poles
• sister chromatids separate
Telophase II and Cytokinesis
• chromosomes arrive at opposite poles (began moving in anaphase II) • eventually results in 4 haploid daughter cells that vary from their parents and siblings
• results from independent assortment of chromosomes (homologs orienting randomly), crossing over, random fertilization
• mutations are the original source for genetic variation
Mendel and Transmission Genetics
Mendel studied seven characteristics of pea plants: flower color, flower position, seed color, seed shape, pod shape, pod color, stem length. Mendel discovered dominant and recessive traits. If the dominant trait is present in an organism, that is what we see. For the recessive trait to be seen, the genotype must be both recessive.
EXAM 3 STUDY GUIDE: BSC 197 4
• Phenotype: the appearance of an organism caused by its genotype; EX: if red color is the dominant trait, the flower looks red; red color/dominant is the phenotype • Genotype: the genetic makeup causing the phenotype
• Homozygous: an organism with two identical alleles for a specific trait • Heterozygous: an organism with two different alleles for a specific trait
For Mendel’s experiment, he began with two true breeding parents. He then crossed these to create offspring (the F1 generation). He then crossed the F1 generation to create offspring, known as the F2 generation.
Major Concepts of Mendel’s Work
• A gene has alternative versions which can cause variations in traits. We know call the gene alternatives alleles.
• For every trait, an organism inherits an allele from each parent. An organism could get two different alleles or two identical alleles.
• An organism with a dominant and recessive alleles will ALWAYS express the dominant trait
• Only when the organism has both recessive alleles will the recessive allele be expressed
Mendel’s exact ratios have not yet to be reproduced. Mendel achieved very clearcut ratios however no scientist has been able to reproduce the results. Mendel’s ratios are similar to the results of pencil-and-paper punnet squares:
This Punnet square is a heterozygous parent
crossed with a homozygous parent. All the
offspring will express the dominant trait.
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Chromosomal Basis of Inheritance
Thomas Hunt Morgan
Morgan came after Mendel and experimented with fruit flies. He provided evidence which showed that genes were located on the chromosome.
• wild type: the normal phenotype
• mutant phenotype: different phenotype compared to the wild type
• Sex chromosomes: X and Y, XX = female, XY = male
• A gene of a sex chromosome is called a sex-linked trait even if it is unrelated to sex • In females, the embryo will inactivate one of the two X chromosomes randomly. The inactive X chromosome becomes a Barr body.
• Mosaicism: If a female is heterozygous for a certain trait, she will become a mosaic for that trait after X chromosome inactivation.
A linked gene refers to genes on the same chromosome that are commonly inherited together. Morgan reasoned that these genes do not sort independently because they are on the same chromosome.
Aneuploidy: incorrect number of chromosomes
Polyploidy: too many chromosomes
Major Chromosomal Modification Events:
Replication and Repair
• Semi-conservative replication: the existing DNA strands are separated and a new strand is created. The new double-stranded DNA molecule consists of one old and one new strand.
1. The double stranded DNA molecule is separated by an enzyme known as helicase. The unwinding begins at the origin of replication. The strands want to reconnect, or reanneal, so single stranded proteins bind to the bases to prevent that.
2. DNA polymerase duplicates strand
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3. DNA-RNA duplex is constructed by primase and attaches the complimentary base pairs to the strand
4. DNA ligase connects the two strands and then polymerase proofreads the new strand.
Mutation and Repair
• UV rays
• free radicals
• Mismatch: an incorrect base pair is corrected by enzymes
• Nucleotide Excision Repair: nuclease cuts out and replaces damaged pieces of DNA
Transcription & Translation
• synthesis of RNA directed by DNA (transcription)
• produces messenger RNA (mRNA)
• use of mRNA template to synthesize new proteins (translation)
• Initiation: RNA polymerase binds to DNA
• Elongation: polymerizes complimentary ribonucleotide bases to make an RNA molecule
• Termination: polymerase stops synthesizing RNA and the RNA folds on itself
• Initiation: ribosome binds to mRNA near AUG codon
• Elongation: addition of new amino acids
• Termination: protein synthesis stops and the ribosome detaches from mRNA
Both of these are complicated processes. Above is a basic explanation of each stage. If you would like a more in-depth explantation, check out the following link: http:// www.genome.gov/27552603
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Promotors and Operators
An operator is the regulatory switch which is a segment of DNA. The operator and promotor are usually within close proximity. The operon is a stretch of DNA that contains the promotor, the operator, and the genes controlled by the promotor and operator.
Repressors and Corepressors
The repressor is responsible for switching the operon off. It can also prevent gene transcription. To do so, it will bind to the operator which blocks RNA polymerase. The corepressor helps the repressor to switch off the operon.
Anabolic and Catabolic Pathways
Catabolic pathways typically use inducible enzymes. A chemical signal causes the synthesis of these enzymes to begin. Anabolic pathways typically use repressible enzymes. The synthesis of repressible enzymes is repressed by high end product levels.
Prokaryotes and Eukaryotes: Gene Regulation
A big difference between prokaryotic and eukaryotic gene regulation is the life span of mRNA. Protein synthesis is greatly determined by the how long the mRNA molecules live in the cytoplasm. Eukaryotic mRNA molecules have a much longer lifespan than prokaryotic mRNA. The life span of an mRNA molecule is determined by sequences in the DNA.
Post-transcriptional Modification Events
Once translation occurs protein processing can occur. This could include degradation by the proteasome or the addition of chemical groups.
Evolution and Genomes
Prokaryotes, such as bacteria, keep the replication process as quick as possible. They have evolved to delete genes not needed in their genome (this process is called genome reduction). Eukaryotes, unlike prokaryotes, will add to their DNA over time.
Methods of Changing
1. Some cells have the ability to take DNA from their outside environment and integrate it into their own DNA cells. Some bacterial cells can do this.
1. Bacterial cells can exchange DNA material through a thin tube called a pilus. EXAM 3 STUDY GUIDE: BSC 197 8
1. DNA material movement between bacterial cells facilitated by bacteriophages.
Horizontal Transfer: DNA material taken from an outside source. The above numbered points show the three main methods of horizontal transfer.
Transposable elements are pieces of DNA that will replicate and move, or transpose, to other ares of the cell.
Hardy Weinberg Equations
Assumptions to use the equations:
1. No new organisms can enter the environment 2. System must be at equilibrium
3. No new conditions causing different selective pressures than before
Equation 1: p + q =1
Equation 2: p2 + 2pq + q2 = 1
where p is allele frequency of the dominant allele and q is the allele frequency of the recessive allele EXAM 3 STUDY GUIDE: BSC 197 9