Bio Exam 3

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mutation

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heritable change in genetic material

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point mutation

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affects a single nucleotide, can alter coding sequence of DNA (silent, missense, nonsense, and frameshift mutations)

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Spontaneous mutation

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the result of errors in natural biological processes

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Induced mutation

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due to agents in the environment that cause changes in DNA structure

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How can mutagens alter DNA?

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changing the nucleotide structure, mimicking the normal bases, and alkylating bases

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What does a DNA repair system involve?

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proteins that sense DNA damage and repair it before a mutation occurs

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Nucleotide excision repair

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recognizes various types of DNA repair (thymine dimmers) or several nucleotides!!!

--excises damaged strand and new strand is made

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Xeroderma pigmentosum

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one inherited disease that is caused by defects in nucleotide excision repair

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Mismatch repair systems

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recognize a base mismatch that is due to an error in DNA replication, the mismatched nucleotide is enzymatically removed

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Oncogenes

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=cancer-causing genes, produced through mutations in proto-oncogenes

--often encode proteins involved in cell-signaling pathways that promote cell division

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Missense mutations, gene amplifications, chromosomal translocations, and retroviral insertion

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4 common genetic changes that can turn proto-oncogenes into oncogenes

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What type of mutation would cause the GCPR pathway to be always "on"

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a mutation that inhibits the ability of the Ras protein to hydrolyze its GTP converts the ras gene into an oncogene

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Philadelphia chromosome

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a chromosome translocation that fuses part of the bcr gene and abl gene-->also creates an oncogene that causes leukemia

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tumor-suppressor genes

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--often encodes proteins that are checkpoint proteins or negative regulators of cell division

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Rb protein tumor suppressor

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negative regulator of cell division because it inhibits E2F, a transcription factor that promotes cell division

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p53

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tumor suppressor, guardian of the genome for which a knockout mouse exists

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common ways that tumor suppressor genes are inactivated

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gene mutations, chromosome loss, and DNA methylation

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DNA-protein complex that makes up chromosomes

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chromatin

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nucleosomes

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DNA wrapped around histone proteins, repeating structural unit in eukaryotic chromatin

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effects of acetylation on nucleosomes

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=addition of acetyl groups to histone tail

--modification can control degree of compaction

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euchromatin level of compaction

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formation of radial loop domains in which the bases of the 30-nm fibers are anchored to the nuclear matrix

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What is required for chromosome compaction to produce a metaphase chromosome?

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--conversion of all euchromatin (expressed) to heterochromatin (not expressed)

--Gene expression is controlled by the level of compaction of the chromatin.

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one way to control level of compaction

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--the pattern of covalent modification of amino terminal tails of histone proteins, or histone code

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genome

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cell's endowment of DNA, its genetic information

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How does duplicated DNA fit in cell before it divides?

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--the chromatin condenses, it becomes densely coiled and folded making the chromosomes much shorter and thicker

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sister chromatids

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--2 chromatids in each duplicated chromosome that contain identical copies of the chromosome's DNA molecule
--they're initially attached by proteins along their length, but in the condensed form-->narrow "waist" at specialized region called centromere

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Interphase

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--when the cell grows and copies its chromosomes in preparation for cell division
--the cell grows by producing proteins and cytoplasmic organelles

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Subphases of interphase

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G1 phase-(first gap) cell grows
S phase-"synthesis of DNA" cell continues to grow, copies its chromosomes
G2 phase-(second gap) grows more as it completes preparation for division

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M phase and cytokinesis

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Mitosis phase-divides the nucleus and distributes its chromosomes to the daughter nuclei
Cytokinesis-divides the cytoplasm producing 2 daughter cells

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5 subphases of mitosis

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*Prophase-sister chromatids condense and spindles start to form; nuclear membrane begins to dissolve

*Prometaphase-nuclear membrane completely gone and spindles fully formed; sister chromatids attach to spindles via kinetochore microtubules

*Metaphase-sister chromatids align along metaphase plate

*Anaphase-sischrom separate and individual chromosomes move toward poles as kinetochore microtubules shorten; polar microtubules lengthen and push poles apart

*Telaphase-chromosomes decondense and nuclear membranes reform; cleavage furrow separates 2 cells

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Cytokinesis in animals

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-occurs by the process of cleavage; cleavage furrow begins as a shallow groove in the surface of the cell near the surface of the cell

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Cytokinesis in plants

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--no cleavage furrow bc plants have walls
--instead vesicles derived from the golgi apparatus move along microtubules to the middle of the cell, where they coalesce producing a cell plate

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Mitotic spindles

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--fibers composed of microtubules and associated proteins that distribute chromosomes to daughter cells (include polar, astral, and kinetochore)
--major driving force in mitosis

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Centrosome

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--location where assembly of spindle microtubules begins (microtubule organizing center)
--by end of prometaphase, centrosomes develop as spindle poles at opposite ends of the cell

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role of meiosis in sexual life cycle

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--fertilization and meiosis alternate in sexual life cycles
-meiosis reduces chromosome number from diploid to haploid

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How can you distinguish between the 46 chromosomes in humans?

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-size
-position of centromere
-pattern of staining with certain dyes

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karyotype

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--ordered display of individual's chromosomes used to determine chromosomal abnormalities like in aminocentous

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homologous chromosome pairs

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--carry genes that control the same inherited characteristics
--consequence of sexual reproduction

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Gamete chromosomes

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--sperm cells or ova have only set of chromosomes: 22 autosomal and an X or Y

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fertilization

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-by means of sexual intercourse, the haploid sperm cell and haploid ova fuse together (syngamy)

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zygote

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-fertilized egg containing 2 haploid sets of chromosomes bearing genes from the maternal and paternal family lines

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Gametes developed in the gonads

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-NOT produced by mitosis..if they were you'd have 4 sets of chromosomes after 1 generation and 8 after a second, etc

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Meiosis

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--gametes undergo this process in which the chromosome number is halved
--meiosis consists of 2 consecutive cell divisions Meiosis I and Meiosis II which produce 4 daughter cells each with only half the chromosomes of the parent cell.

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Homologous pairs vs. sister chromatids

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-h.p. are individual chromosomes that were inherited from different parents

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Phases of Meiosis

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*Interphase I-chromosomes replicate-->sister chromatids; forms a diploid cell

*Meiosis I-homologous pair of replicated chromosomes separates forming 2 haploid cells containing sischrom

*Meiosis II-sister chromatids in each cell separate to form 4 haploid cells with unreplicated chromosomes

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3 events unique to meiosis occurring in the first division cycle

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*Prophase I-homologous chromosomes pair up in process called synapsis

*Metaphas I-homologous pairs aligned along metaphase plate (in humans you see 23 tetrads)

*Anaphase I- homologous chromosomes (not sister chromatids) separate and are carried to opposite poles of cell

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key differences between mitosis and meiosis

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--chromosome number reduced by half in meiosis but not mitosis; the geneitc consequences of this difference are very important
--Mitosis produces daughter cells identical to the parent cell and to each other. Meiosis produces daughter cells that are different from the parent cell and from each other.

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synaptonemal complex

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-protein "zipper" that holds homologues tightly together all along their lengths during part of prophas I

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chiasmata

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physical manifestation of genetic rearrangement called crossing over

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3 mechanisms that contribute to genetic variation

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1. independent assortment-->due to random orientation of tetrads at metaphase plate
2. crossing over bt homologous chromosomes during prophase I
3. random fertilization of an ovum by a sperm

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recombinant chromosomes

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--produced by crossing over
--combine genes from each parent

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Gregor Mendel's discoveries

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--brought an experimental and quantitative approach to genetics
--law of segregation=2 alleles for a characteristic are packaged into separate gametes
--law of independent assortment=each pair of alleles segregates into gametes independently
--mendelian inheritance reflects rules of probability
-Mendel discovered particulate behavior of genes

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Mendel's analysis of F2 generation

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--revealed 2 fundamental principles of heredity that are now known as the law of segregation and the law of independent assortment

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pedigree analysis

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information about the presence/absence of a phenotypic trait is gathered from as many individuals in a family as possible and across generations.

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amniocentesis

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--fetal cells extracted from amniotic fluid beginning at the 14th to 16th week of pregnancy
--used to assess the presence or absence of a specific disorder

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Chorionic Villus Sampling (CVS)

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--another test to determine if a child has a disorder, extracts a sample of fetal tissue from the chorionic villi of the placenta
--allows for faster karyotyping and can be performed as early as the 8th to 10th week

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Chromosomal abnormalities

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major chromosome aberrations and their consequences produce exceptions to standard chromosome theory

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Nondisjunction

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--occurs when problems with the meiotic spindles cause errors in the daughter cells
--may happen if tetrads dont separate properly in meiosis I or alternatively the sister chromatids may fail to separate during meiosis II

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aneuploidy

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abnormal chromosome number

ie. trisomic-3 copies of particular chromosome (2n+1)
monosomic-has only 1 copy of a chromosome (2n-1)

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Hemophilia A is caused by...

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...a recessive X-linked gene

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Mendelian inheritance

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--inheritance pattern of genes that segregate and assort independently
--simple mendelian inheritance-one trait dominant over another
--X-linked inheritance-pairs of dominant and recessive alleles found on X Chromosome

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wild type allele

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-prevalent allele in a population
-encodes a protein made in the proper amount and functioning normally

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mutant allele

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--altered by mutation
--defective in its ability to express a functional protein

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incomplete dominance

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--heterozygote has an intermediate phenotype

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4 types of changes in chromosome structure due to chromosomal breakage

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1. deletion-chromosome fragment lacking a centromere is lost during cell division
2. duplication-fragment becomes attached as an extra segment to a sister chromatid
3. inversion-chromosomal fragment reattaches to original chromosome but in the reverse order
4.translocation-chrom fragment joins a nonhomologous chromosome

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Down Syndrome

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-aneuploid condition with 3 copies of chromosome 21
-most cases result from nondisjunction during gamete production in one parent

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Particulate Inheritance Theory

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determinants of inheritance are transmitted intact from generation to generation

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Pleiotrophy

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mutation in a single gene can have multiple effects

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Klinefelter's Syndrome

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XXY-->sexual immaturity (no sperm) breast swelling (males)

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What mechanisms ensure that the DNA sequence in the genome remains accurate?

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-excision repair
-complementary base pairing during DNA replication
-mismatch repair
-proofreading during DNA replication

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The most reasonable inference from the observation the defects in DNA repair enzymes contribute to some cancers is that...

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...uncorrected changes in DNA can lead to cancer

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Cells use special enzymes to fix incorrectly paired nucleotides in...

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...mismatch repair

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Mutagens disrupt basepairing by:

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ALL OF THE ABOVE

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Which system repairs DNA damage that includes the removal/repair of several nucleotides?

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Nucleotide excision repair

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Chronic mylogenous leukemia is the result of the expression of the "philadelphia chromosome." The philly chrom is an example of which genetic change resulting in the mutation of a proto-oncogene?

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chromosomal translocation

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The p53 knockout mouse is born healthy but

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does not express wild-type p53 and easily develops cancer

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The "two-hit" model for retinablastoma (Rb) inactivation results in..

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..an E2F protein that is always active, resulting in uncontrolled cell division.

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The most common mechanism resulting in the loss of tumor suppressor gene function include..

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..mutation
chromosome loss
abnormal methylation of CpC islands near promoter regions

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The major difference between hyperplasia and dysplasia is

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hyperplasia is an increase in cell number, dysplasia has a change in cell morphology

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Which histone is not part of the octamer found in the nucleasome?

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H1

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Which level of compaction interacts with the nuclear matrix?

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30-nm fiber

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Which of the following covalent modification play a role in regulating DNA compaction as put forth by the histone code hypothesis?

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--phosphorylation
--acetylation

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The spindle microtubules involves which of the following?

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--astral
--polar
--kinetochore

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Regarding mitosis and cytokinesis, one difference between higher plants and animals is that in plants

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a cell plate begins to form at telophase whereas in animals a cleavage furrow is initiated at that stage.

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How do the daughter cells at the end of mitosis and cytokinesis compare with their parent cell when it was in G1 of the cycle?

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--the daughter cells have the same number of chromosomes and the same amount of DNA

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Taxol is an anticancer drug. In animals taxol disrupts microtubule formation by bonding to microtubules and accelerating their assembly from the protein precussor, tubulin. Surprisingly, this stops mitosis. Specifically taxol must affect

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the fibers of the mitotic spindles

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In some cells, replicated chromosomes are lined up on the equator of the cell. These particular cells are in what stage of mitosis?

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metaphase

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Spindle fibers attach to kinetochores during...

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...prometaphase

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What is a karyotype?

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a display of every pair of homologous chromosomes within a cell, organized according to size and shape

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Synapsis of homologous pairs occurs in this stage; crossing over may occur

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prophase I

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If a chromosome lacks certain genes what most likely occurred?

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deletion

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One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. This is called a...

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translocation

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A cell that has 2n+1 chromosomes is

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--trisomic
--anueploid