visual summary notes

what does asexual reproduction produce?

clones- genetically identical offspring

what do sexual life cycles involve?

meiosis and fertilization

in what organism are cell division and reproduction the same thing?

single-celled organisms

what is the difference between an asexual and a sexual life cycle?

asexual: has asexual cell division meaning offspring are identical to each other and the parents

sexual: has meiosis and fertilization, so offspring differ from one another and their parents

what is the difference between a diplontic and haplontic life cycle?

diplontic: the mature organism is diploid and the gametes are the only haploid stage

haplontic: the mature organism is haploid and the zygote is the only diploid

what does cell division signals lead to?

DNA replication, DNA segregation, and cytokinesis

where do DNA replication and segregation co-occur at?

in binary fission

how do condensed chromosomes move in mitosis?

characteristic stages that involves a microtubule spindle

what events occur during G1, S, G2, and M phases of the cell cycle?

G1: preparation for cell division

S: DNA replication

G2: preparation for mitosis

M: mitosis and cytokinesis (segregation of one sister chromatid from each chromosome into daughter cells)

what events occur at prophase, prometaphase, metaphase, anaphase and telophase of mitosis?

prophase: centrosomes divide, chromosomes condense, spindle start to form

prometaphase: nuclear envelope breaks down, chromosomes attach to fully formed spindle

metaphase: alignment of replicated chromosomes on the metaphase plate

anaphase: centromere division and movement of sister chromatids to opposite poles

telophase: decondensing of chromosomes and re-formation of nuclear membranes

how does binary fission differ from the mitotic cell cycle?

the main difference is the co-occurrence of DNA replication and segregation in binary fission

binary fission in prokaryotes does not use a microtubule spindle

what are the products of meiosis?

4 haploid cells with unreplicated chromosomes

what are the 2 sequential cell divisions of meiosis?

meiosis I: separation of homologous chromosomes

meiosis II: separation of sister chromatids

what produces genetic variation among the gametes produced by meiosis?

independent assortment of chromosomes and crossing over

how many alignments at metaphase I are possible when 2n=6?

with three pairs of chromosomes (n=3_ there are 2³ = 8 possible alignments if we distinguish the two poles at meiosis I

in terms of generating different gametes, there are only four possible alignments

what chromatids can be involved in crossing over?

only nonsister homologous chromatids that are paired during prophase I

what does nondisjunction lead to?

aneuploidy

what leads to polyploidy?

cytokinesis failure and polyspermy

what happens during nondisjunction?

two chromosomes that should have gone to opposite poles go to the same pole

why do aneuploid cells often show reduced survival?

the imbalance of chromosomes set (one or three chromosomes instead of two) causes harm to cells

define polyploidy and explain how it differs from aneuploidy

polyploidy occurs when a cell or organism has the same number of additional copies of all chromosomes

aneuploidy occurs when a cell or organism has an equal number of copies of each chromosomes

what is included in the eukaryotic cell cycle?

restriction point and three additional cell cycle checkpoints

what do cyclins and cyclin-dependent kinases (CDKs) play a major role in?

cell cycle regulation

what are some of the ways that cells die?

due to damage, lack of nutrients, or programmed cell death

in eukaryotes, what factors can cause cell cycle arrest at the four checkpoint?

restriction point (G1 checkpoint): DNA damage, insufficient resources, no external signal to divide

why aren’t all CDKs active throughout the cell cycle?

to be active, CDKs must have their cyclin bound

cyclins are only present for certain parts of the cell cycle and then are quickly degraded

why might a cell undergo apoptosis?

because it is worn out, in the wrong place, infected with a pathogen, or has reached its hayflick limit (maximum number of cell divisions)

how is cell cycle control involved with cancer?

cell cycle controls at various checkpoints are not functional in cancer cells which allows uncontrolled cell division

how do alleles of a gene segregate?

they segregate equally into gametes, producing a 3:1 phenotypic ration in the F2 generation in a mendelian monohybrid cross

how do alleles of different genes assort independently into gametes?

produce a 9:3:3:1 phenotypic ration in the F2 generation of a mendelian dihybrid cross

a test cross is made between a BbCc individual and a bbcc individual. assuming mendel’s laws hold, what are the expected genotypes in the offspring?

¼ BbCc, ¼ Bbcc, ¼ bbCc, ¼bbbc

a man with a rare Mendelian disorder has a father and grandmother who are also affected. no one else in his family, including his two children are affected. what does this indicate about the inheritance of the disorder?

that it is dominant: dominant disorders do not skip generations looking backward (affected individuals always have an affected parent)

what does separation of homologs during anaphase I explain?

the law of segregation

what does independent alignment of chromosome pairs at metaphase I and crossing over at prophase I support?

the law of independent assortment

what do sex-linked traits show?

unusual inheritance patterns consistent with being inherited on a sex chromosome

for genes on separate chromosomes, draw the chromosomal alignment at metaphase I for a cell in an AaBb individual that will give rise to two Ab and two aB gametes.

explain why men are more commonly affected by X-linked recessive traits than women are

in men, a single copy of the recessive allele will cause the trait to be expressed because there is only one copy of the gene- men are hemizygous

in women two copies of the recessive allele are needed, which is much less likely to occur

explain why men affected with rare x-linked recessive trait seldom have affected sons

the x chromosome carried by men is passed to all of their daughters but not to sons, the sons receive only their father’s Y chromosome

for an affected male to have an affected son, his partner would have to either be affected or be an unaffected heterozygote (a carrier) both of which are unlikely for rare disorders

what do genes that have multiple alleles show?

complete dominance, incomplete dominance, or codominace

how does epistasis work?

the phenotype caused by one gene is affected by the genotype at one or more other genes

what is phenotypic plasticity?

the observed phenotype can be altered by environmental conditions

in a mendelian monohybrid cross, the F2 generation consists of one-fourth red-flowered, half pink-flowered, and one-fourth white-flowered individuals. what does this indicate?

a single gene controls flower color, with red and white alleles producing red homozygotes, pink heterozygotes, and white homozygotes

the red allele shows incomplete dominance

a black lab is crossed with a yellow lab, and half the offspring are black and half are brown. what are the genotypes of these two dogs?

the yellow parent is ee and since no offspring are yellow, the black parent must be EE at the deposition gene

since half the offspring are black and half are brown, the black parent must be heterozygous Bb and the yellow parent must be homozygous bb

in winter, Siamese cats have darker faces than they do in the summer. what is one explanation for this observation

it indicates that fur color in these cats may be affected by temperature

how are plasmids passed to other cells?

via bacterial conjugation

how can prokaryotes exchange chromosomal material?

by transformation and conjugation

what is a sex pilus?

a structure composed of proteins and phospholipids that can attach one prokaryotic cell to another, bringing them together and triggering the formation of a conjugation tube through which single-stranded DNA can pass during conjugation

what is the difference between the donor cell and the recipient cell in bacterial conjugation?

the donor cell makes pili and is the donor of the DNA that passes through the conjugation tube

the recipient cell receives the DNA

are crossovers needed to transfer genetic material during conjugation and transformation?

plasmids can be transmitted during conjugation and do not need a crossover even to be retained in the recipient cell

however, if chromosomal DNA passes from a donor to a recipient, or if DNA is taken up form the environment, two crossovers are needed to insert alleles from such linear molecules into the recipient circular chromosome

how was DNA shown to be the molecule of inheritance by the Hersey-Chase experiment?

bacteriophage injected their DNA and not protein into bacteria that then manufactured more phage

who came up with the three-dimensional model of DNA?

Watson and Crick which also obeyed Chargaff’s rules and was consistent with Franklin’s x-ray diffraction data

what did Chargaff discover about DNA that helped determine its structure?

that the amount of A = T and the amount of G = C

if a strand of DNA has sequence 5’- ATCCGTTA-3’, what is the sequence of the complementary strand?

3’- TAGGCAAT-5’

what does it mean to say that each strand in a DNA helix has directionality?

the two strands of DNA are antiparallel

one end of a strand has a 5’ phosphate and the other has a 3’ hydroxyl group

how did Meselson and Stahl show that DNA replicates by semiconservative replication?

they grew bacteria on media with heavy and light nitrogen

DNA replication begins with ___________ at ori sites and then __________

initiation; RNA priming

how does the leading strand vs the lagging strand differ?

synthesis of the leading strand of the replication fork is continuous whereas synthesis of the lagging strand produces Okazaki fragments

what is the function of telomerase?

functions to lengthen chromosome ends to compensate for the shortening that occurs with every cell division

why is it important that an ori be used only once during DNA replication?

the cell cycle results in the production of two cells, each of which receives a complete copy of the genome

if an ori started replication more than once per cell division, then some regions would be replicated more than others, leading to problems moving DNA molecules to both daughter cells during mitosis, and to problems with incorrect gene expression

what is the function of DNA ligase in replication?

it seals the single-strand breaks that are left after RNA primers are removed from the lagging strand

why are telomeres short in the liver cells but not in the gametes of an adult?

because telomerase is not expressed in adult liver cells but is expressed in the germ line cells

how can errors and introduce mismatches made by DNA polymerases be corrected?

by proofreading or by mismatch repair

what do chromosomal rearrangements include?

deletions, duplications, inversions, and translocations

under what conditions will a DNA polymerase error lead to a mutation?

an error in adding the incorrect base in terms of the DNA template causes a mismatch

if the mismatch is not repaired by proofreading or by mismatch repair before the next round of replication, or it it is repaired incorrectly, the result will be a base-pair substitution

what would be the effect on the organism of a genetic mutation that prevented any further DNA repair from ocurring?

damaged DNA and mismatched DNA would be unrepaired, resulting in very high mutation rate and would probably lead to death

what are the two mechanisms that cause chromosomal rearrangements?

crossing over and DNA damage can cause the double-strand breaks that result in chromosomal rearrangements

what did the experiments with knockouts in metabolic pathways lead to?

the one gene-one polypeptide hypothesis

what does the central dogma of molecular biology state?

that DNA is transcribed into messenger RNAs, which are then translated into polypeptides

what are the three most common kinds of RNAs in a cell?

rRNAs (80%), tRNAs (15%), and mRNAs (5%)

what do promoters do?

direct RNA polymerases to genes, initiating RNA synthesis

in the elongation phase of RNA synthesis, ribonucleotides that are complementary to the DNA template are added to what end of the RNA?

the 3’ end

in eukaryotes, mRNA processing involves what?

removing introns and adding a 5’ cap and a 3’ poly a tail to the ends of the pre-mRNA transcript

what three mRNA processing events occur in eukaryotes?

intron removal

5’ capping

addition of a 3’ poly A tail

will a mutation at a promoter always cause reduced gene expression?

no, some promoters have sequences that cause low levels of transcription

altering their sequence could change them so they bind RNA polymerase better, causing higher expression of the gene

how does the structure, transcription, and processing of a prokaryotic and eukaryotic protein-coding gene differ?

prokaryotes

• no introns in the gene so coding sequence is not interrupted

• no processing of the mRNA

eukaryotes

• introns are present which interrupt the protein-coding sequence

• RNA processing during which a 5’ cap and a 3’ poly A tail are added and introns are removed

the _______ is degenerate, with 61 ________ and 3 ________

genetic code; sense codons; nonsense codons

how can the effect of a base substitution at a codon be predicted?

using the genetic code

how do you distinguish among synonymous, missense, loss-of-stop, and nonsense mutations with respect to their effect on a protein

all 4 types of mutations result from a base substitution that changes a codon

synonymous

• do not cause an amino acid substitution

missense

• cause a change in one amino acid

loss-of-stop

• change a stop codon into a sense codon (making protein longer)

nonsense

• change a sense codon into a stop codon (making protein shorter)

what is a frame-shift mutation and what is its effect on a protein?

ribosomes begin DNA synthesis at the start codon AUG and then read 3 bases at a time

a mutation that inserts or deletes a number of bases in an exon that is not a multiple of 3 will cause a frame shift, such that codons are no longer in the correct reading frame

the primary structure of a protein will be incorrect starting at the location of the frame shift and will likely be shorter

how is a tRNA charged?

by adding the appropriate amino acid to its 3’ end and has an anticodon for paring with a codon

what 3 stages does translation take place in?

1. initiation (with methionine at AUG)

2. elongation

3. termination (at UAA, UGA, or UAG

how is an mRNA recognized by a ribosome?

in prokaryotes a sequence near the 5’ end of the mRNA is recognized

in eukaryotes ribosomes recognize the 5’ cap

what are the functions of the 3 most common kinds of RNAs in a cell?

mRNAs encode protein information

rRNAs are part of ribosome and perform some of its enzymatic functions

tRNAs can read 1-3 codons (using its anticodon) and bring in the appropriate amino acid during translation

how are proteins targeted to particular organelles?

with signal sequences

are many proteins modified after translation?

yes

what is the function of a signal sequence?

direct proteins to their appropriate cellular compartment

proteins that end up in the cytosol do not need signal sequences

in what ways does the functional form of a protein differ from the amino acid sequence encoded in the exons of its genes?

terminal amino acids may be missing-methionine at the amino end is often removed and a piece from the amino or carboxyl end many be removed if proteolysis occurs during processing

amino acids may be modified by the addition of phosphates, sugars or various other compounds

when can gene expression be regulated?

before transcription, during transcription, or after transcription

before translation, during translation and after translation

when are constitutive genes expressed?

expressed at all times in all tissues

can the expression of inducible and repressible genes be turned on and off?

yes

what is transcription controlled by?

by positive or negative regulation or by both

in bacteria, some genes are used to synthesize amino acids and some are used to break down amino acids as an energy source. do you expect these genes to be inducible, repressible, or constitutive?

amino acid biosynthesis: repressible

amino acid breakdown: inducible

how can negative regulators be involved in the control of transcription both for inducible and for repressible genes?

positive: binding of an activator increases transcription

negative: binding of a repressor decreases transcription

many genes in prokaryotes are co-regulated in ______

operons

when is the lac operon expressed?

when glucose levels are low and lactose levels are high

does lac operon have both negative and positive regulation?

yes negative regulation is lactose control and positive regulation is glucose control

what is the defining characteristic of a prokaryotic operon?

it has a single promoter that initiates transcription of an RNA that contains two or more non-overlapping genes

what does initiation of transcription in eukaryotes involve?

assembly of the basal transcription apparatus followed by interactions with specific transcription factors through mediator

what do enhancers and silencer do?

bind specific transcription factors and may be far from the promoter

differences in transcription factors underlie ______________

cell differentiations