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3 predominant stages in interphase of cells which are active in the cell cycle.
- -G1: the cell grows and proteins necessary for cell division are synthesized G1/S checkpoint near the end of G1; hold the cell in G1 until the cell has all of the enzymes necessary for the replication of DNA
- -S phase: synthesis of DNA
- -G2: in this phase, several additional biochemical events necessary for cell division take place.
- -G2/M checkpoint is reached near the end of G2 ; this checkpoint is passed only if the cell is ready to divide and enter M phase
Stages of mitosis and the major events that take
place in each stage
- - Prophase: chromosomes condense and mitotic spindle forms
- - Prometaphase: nuclear envelope disintegrates, and spindle microtubules anchor to kinetichores
- - Metaphase: chromosomes align on the metaphase plate
- - Anaphase: sister chromatids separate, becoming individual chromosomes that migrate toward spindle poles
- - Telophase: chromosomes arrive at spindle poles, the nuclear envelope re-forms, and the condensed chromosomes relax
Stages of meiosis and major events that take
- Meiosis I
- - Prophase: chromosomes condense, homologous chromosomes synapse, crossing over takes place, nuclear envelope breaks down, and mitotic spindle forms
- - Metaphase I: homologous pair of chromosomes line up on the metaphase plate
- - Anaphase I: the 2 chromosomes (each with 2 chromatids) of each homologous pair separate and move toward opposite poles
- - Telophase I: chromosomes arrive at the spindle poles
- - Cytokinesis I: the cytoplasm divides to produce 2 cells, each having half the original number of chromosomes
- Meiosis II
- - Prophase II: chromosomes condense, the spindle forms, and the nuclear envelope disintegrates
- - Metaphase II: individual chromosomes line up on the metaphase plate
- - Anaphase II: sister chromosomes separate and move as individual chromosomes toward the spindle poles
- - Telophase II: chromosomes arrive at the spindle poles; the spindle breaks down and a nuclear envelope reforms
- - Cytokinesis: the cytoplasm divides
What two processes unique to meiosis are
responsible for genetic variations?
Crossing over and random assortment
Explain how a retrovirus, which has an RNA
genome, is able to integrate its genetic material into that of a hosting having a DNA genome.
Because the retroviral genome is RNA, whereas that of the host is DNA, a retrovirus must produce reverse transcriptase, an enzyme that synthesizes complementary DNA from either an RNA or a DNA template. A retrovirus uses reverse transcriptase to make a double-stranded DNA copy from its single-stranded RNA genome. The DNA copy then integrates into the host chromosome to form a provirus, which is replicated by host enzymes when the host chromosome is dublicated
Difference between a “crossover event” and a
- Crossover event: in which the genes on either end of the molecules are different from those originally present
- Noncrossover event: in which the genes on either end of the molecules are identical with those originally present
What are the 3 basic stages of transcription?
What are the 2 basic types of terminators found
in bacterial cells?
- Rho d….(dependent)
What are two distinct functions of transcriptional activator proteins?
- 1. Capable of binding DNA at specific base sequence
- 2. The ability to interact with other components of the transcriptional apparatus and influence the rate of transcription
6 levels at which gene expression might be controlled
- 1. through the alteration of gene structure
- 2. at the level of transcription
- 3. mRNA processing
- 4. the regulation of RNA stability
- 5. at the level of translation
- 6. posttranslational modification
What is the difference between positive and negative control?
Positive control in which a regulatory protein is an activator, stimulating transcription. Negative control, in which a regulatory protein is a repressor, binding to DNA and inhibiting transcription.
What is the difference between inducible and repressible operons?
Inducible operons are those in which transcription is normally off (not taking place); something must happen to induce transcription, or turn it on. Repressible operons are those in which transcription is normally on (taking place); something must happen to repress transcription, or turn it off.
Briefly explain how transcriptional activator proteins and repressors affect the level of transcription of eukaryotic genes
Transcriptional activator proteins bind to the consensus sequence in the regulatory promoter and affect the assembly or stability of the basal transcription apparatus at the core promoter. Transcriptional activator proteins binding to sequences in the regulatory promoter make contact with the mediator and affect the rate at which transcription is activated.
- Repressors bind to sequences in the regulatory promoter or to distant sequences called silencers,
- which, like enhancers, are position and orientation independent. These
- repressors may compete with activators for DNA binding sites; a repressor may
- bind to sites near an activator site and prevent the activator from contacting
- the basal transcription apparatus, or could directly interfere with the
- assembly of the basal transcription apparatus, thereby blocking the initiation
- of transcription.
What is an insulator?
An insulator is a DNA sequence that blocks or insulates the effect of an enhancer; must be located between the enhancer and the promoter to have blocking activity; also may limit the spread of changes in chromatin structure.
What is a response element? How do response elements bring about coordinated expression of eukaryotic genes?
A common DNA sequence found upstream of some groups of eukaryotic genes. A regulatory protein binds to a response element and stimulates the transcription of a gene. The presence of the same response element in several promoters or enhancers allows a single factor to simultaneously stimulate the transcription of several genes.
What are two distinct functions of transcriptional activator proteins?
- 1. capable of binding DNA at a specific base sequence
- 2. the ability to interact with other components of the transcriptional apparatus and influence the rate of transcription
What are some characteristics of introns?
Common in eukaryotic genes but rare in bacterial genes. In eukaryotic genomes, the size and number of interons appear to be directly related to increasing organismal complexity introns tend to be larger than exons.
What is the function of the spliceosome?
Large structure where spicing of protein-encoding pre-mRNA takes place.
Describe two types of alternative processing pathways. How do they lead to the production of multiple proteins from a single gene?
Alternative splicing in which the same pre-mRNA can be spliced in more than one way to yield multiple mRNA’s that are translated into different amino acid sequences and thus different proteins. Another type of alternative process requires the use of multiple 3’ cleavage sites; two or more potential sites for cleavage and polyadenylation are present in the pre-mRNA.
What is RNA editing?
In RNA editing, the coding sequence of an mRNA is altered after transcription, and so the protein has an amino acid sequence that differs from that encoded by the gene (individual nucleotides in the interior of pre-mRNA may be changed, added, or deleted by RNA editing).
4 types of processing that can take place in pre-mRNA
- 1. the addition of a cap to the 5’ end of the pre-mRNA.
- 2. the 3’ end is cleaved at a site downstream of the AAUAAA consensus sequence in the last exon.
- 3. Immediately after cleavage, a poly(A) tail is added to the 3’ end.
- 4. the introns are removed to yield the mature mRNA.
What is the difference between a backcross and a testcross?
A backcross is a cross between an F1 individual and one of the parental (P) genotypes. Both genotypes are known in this type of cross.
A testcross is a cross between an individual with an unknown genotype and an individual with the homozygous recessive genotype.
Give the typical sex chromosomes found in the cells of people with Turner syndrome, Klinefelter syndrome, and androgen insensitivity syndrome, as well as in poly-X females.
Turner syndrome: XO
Klinefelter syndrome: mostly XXY but sometimes XXXY, XXXXY or XXYY
Androgen insensitivity: XY
Poly-X females: XXX (and rarely XXXX or XXXXX)
What is the principle of segregation?
The principle of segregation (Mendel's 1st law) states that each diploid individual possesses two alleles at a locus and that these two alleles separate when gametes are formed, one allele going into each gamete.
What is the principle of independent assortment?
The principle of independent assortment (Mendel's 2nd law) states that genes encoding different characteristics (genes at different loci) separate independently
Mendel's 4 "conclusions" from his experiments
- 1. one character is encoded by two genetic factors
- 2. two genetic factors (alleles) separate when gametes are formed
- 3. the concept of dominant and recessive traits
- 4. two alleles separate when equal probability into the gametes
which of Mendel's conclusions support the principle of segregation?
conclusions 2 and 4
What does the term hemizygous mean?
Possession of a single allele at a locus and only applies to the sex chromosome
the failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis
What characteristics are exhibited by an X-linked trait?
X-linked color blindness in humans, males often express the recessive trait, females who are homozygous recessive will express the trait
3 dosage compensation strategies for equalizing the amount of sex chromosome gene products
- 1. can double activity of the gene on the X for males
- 2. can inactivate one of the X chromosomes on females
- 3. can reduce the activity of the genes on both X chromosomes by half
What is the difference between a sex-influenced gene and a gene that exhibits genomic imprinting?
- Sex-influenced gene are encoded by autosomal genes that are more readily expressed in one sex
- Genomic imprinting is differential expression of a gene that depends on the sex of the parent that transmitted the gene
What is incomplete penetrance and what causes it?
Incomplete penetrance is when the genotype does not produce the expected phenotype. This is due to the effects of the other genes and to environmental factors that can alter or completely suppress the effect of a particular gene
How do incomplete dominance and codominance differ?
Incomplete dominance is when the phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the homozygotes. Codominance is when the phenotype of the heterozygote includes the phenotypes of both homozygotes.