Exam 1 Content

Antony van Leeuwenhoeck

a researcher in the 18th century who first described the nucleus as a structure in cells through the observation of amphibian cells

Robert Brown

a researcher in the early 19th century who first named the nucleus; though the structure was reported, the function was unknown

nucleus components

15-20% DNA, 5-10% RNA 15-30% proteins, 40-60% salts

Griffith’s experiment

used two different staphylococcus pneumoniae strains to show how bacteria could be transformed by transferring genetic material from one cell to another, only mice injected with the living S cells died, but mixing living R cells with heat-killed S cells still caused death

virulence

the ability of a virus or a bacterium to cause damage to its host

Avery, McLeod, McCarthy experiment

repeated the Griffith experiment but tested effects of adding RNase, protease, and DNase, found that DNA was the genetic material holding the information in the cell

Hershey and Chase experiments

used radioactively labeled DNA or proteins to follow the radioactive behavior and used a blender to remove bacteriophage ghosts, found that DNA was what caused the cells to become radioactive

bacteriophages

viruses that specifically infect bacteria

nucleotide

the single subunit of DNA made of a sugar, base, and phosphate group

DNA

a polymer of nucleotides that contains the genetic information of an organism, it is made of a deoxyribose sugar, a phosphate group, and a nitrogenous base, encodes for all the proteins made in an organism

Watson and Crick

used light-diffraction patterns to built a model of DNA, identified the double helix structure of two intertwined strands

phosphodiester bonds

covalent bonds between the 3’ hydroxyl of one nucleotide and the 5’ phosphate group of another

antiparallel

DNA strands in a double helix go in opposite directions

complementary base pairing

hydrogen bonds formed between specific bases, two hydrogen bonds formed between adenine and thymine, three hydrogen bonds formed between guanine and cytosine

B-form

the most common DNA shape, a right handed helix with a smooth backbone

Z-form

another possible DNA shape, a left-handed helix with an irregular backbone

semiconservative replication

the actual method of DNA replication postulated by Watson and Crick, where the double helix is unwound and each strand becomes a template to synthesize new strands via complementary base pairing

conservative replication

a proposed method of DNA replication where the original double helix remained intact and both strands of the daughter DNA are newly synthesized

dispersive replication

a propsed method of DNA replication where both strands of both daughter helices have fragments of the original and newly synthesized DNA

Meselsohn and Stahl experiment

used a density gradient of 15N and 14N bacterial DNA to determine method of DNA replication, found that DNA was replicated by the semiconservative model

origins of replication

where DNA replication starts, are multiple, usually ~40,000 bp apart

replication bubble

the expanding area between the two original strands of DNA where new DNA is being synthesized

replication forks

the sites at each of the replication bubble, where new DNA is actively being synthesized

helicase

unwinds DNA at the replication fork to separate the double helix

single-strand binding protein (SSB)

stabilizes the single strands at the replication fork to prevent re-formation of the double helix

gyrase (topoisomerase II)

acts in front of helicase, creating a double-stranded break ahead of the replication fork, swivels the ends and reconnects them to prevent overwinding

DNA polymerase III

forms phosphodiester bonds between adjacent nucleotides to synthesize a new DNA chain, can only synthesize in the 5’-3’ direction

primosome

a protein complex that synthesizes short RNA primers to start new strands for DNA polymerase to continue

RNA primer

a short stretch of RNA synthesized by primase to initiate synthesis of new strands

leading strand

the strand is that synthesized continuously

lagging strand

the strand that is synthesized in Okazaki fragments, due to 5’-3’ synthesis

Okazaki fragments

1000-2000 bp for prokaryotes or 100-200 bp for eukaryotes, DNA fragments that make up the lagging strand

ligase

an enzyme that connects Okazaki fragments by forming phosphodiester bonds between adjacent nucleotides

loop formation

polymerases for both template strands tightly linked together, so a loop formation is required for both strands to be synthesized simultaneously

the central dogma

the idea that genetic information from DNA is transcribed to create mRNA, which is then translated to create proteins

mRNA

messenger RNA, carries genetic information from DNA, read by tRNA for protein synthesis

rRNA

ribosomal RNA, major part of the ribosome

tRNA

transfer RNA, 45 different types, base pairs with mRNA codons to add corresponding amino acids to polypeptide chain

transcription

the process of DNA being used to produce mRNA molecules that will be modified and transported out of the nucleus for translation

RNA

uses ribose as a sugar, has nitrogenous base uracil instead of thymine, is usually single-stranded (can form double stranded structures)

translation

occurs in the ribosome, where all three types of RNA are used to create a protein

codons

non-overlapping groups of 3 bases in mRNA, each corresponds with a specific amino acid

anticodon

a part of the tRNA molecule that base pairs to the mRNA codons to add the correct amino acid to the polypeptide chain

ribosome

an organelle built of a small and large subunit that come together during translation, where translation takes place/where proteins are created

Gregor Mendel’s experiments

first experiment that followed traits over different generations using garden peas, hypothesized that each parent contributed to the traits of their progeny, proposed the idea that heredity determined by genes

self-fertilization

one of the advantages of using the garden pea, easy artificial fertilization

true-breeding

an advantage of using the garden pea, when self-fertilized plants are able to produce only progeny like themselves

genes

the genetic information that determines a trait

alleles

different versions of the same gene, different versions of the same trait

phenotype

the observable trait of an organism

genotype

the genetic makeup of an organism, the collection of alleles an organism has

the law of dominance and uniformity

some alleles are dominant over the other alleles that exist for that gene, if an organism has at least one dominant allele, then the phenotype will reflect the dominant trait

dominant

the allele that controls phenotype in the heterozygous genotype

recessive

the allele that controls phenotype only in the recessive homozygous phenotype

monohybrid cross

a genetic cross between two heterozygous individuals for one gene, will result in a 3:1 ratio for the dominant to recessive phenotype, a 1:2:1 ratio for the dominant homozygous to heterozygous to recessive homozygous genotype

the law of segregation

the two alleles an individual has for each gene separate during gametogenesis, so each parent only passes one allele to their offspring

punnett square

a method to predict offspring ratios

homozygous

when both alleles an individual has for a gene are the samehe

heterozygous

when the alleles an individual has for a gene are different

testcross

a method to determine if an individual is homozygous or heterozygous, cross unknown individual with a homozygous recessive individual, if plant homozygous, all offspring are the same, if plant heterozygous, a 1:1 ratio of the different phenotypes

dihybrid cross

tracing the inheritance of two different traits in the same cross

the law of independent assortment (law of reassortment)

alleles of different genes separate independently of one another during gametogenesis, distributed independently of one another in the offspring of the next generation

linked genes

genes on the same chromosomes that are very close to each other, can not be independently sorted

product rule

the probability of two or more independent events occurring together is equal to the product of their separate probabilities

sum rule

the probability of one or other of two mutually exclusive events occurring is equal to the sum of their separate probabilities

pedigree analysis

a method to trace the inheritance of a certain trait in humans, assume complete penetrance, that the trait is rare in the population (people marrying into the family do not have the mutation, that the trait is not y-linked

incomplete dominance

when the heterozygous genotype is a mixture of the phenotype of both alleles

co-dominance

when the heterozygous genotype shows a combination of the phenotypes of both alleles

wild-type alleles

alleles with frequency greater than 1% in the population, the “normal” alleles found in a population

mutant alleles

rare alleles that have a frequency <1% in the population

monomorphic gene

a gene with only one common, wild-type allele

polymorphic gene

a gene with many wild-type alleles, wild-type alleles called common variants

dominance series of multiple alleles

many alleles for a specific gene can exist in a population, can be completely dominant, incompletely dominant, codominant according to the phenotypes of heterozygotes for the pair

pleiotropy

one gene can affect more than one phenotype

epistasis

in dihybrid crosses, the allele of one gene can hide the effects of other alleles at a second gene

epistatic gene

the gene that is doing the masking

hypostatic gene

the gene that is being masked

locus heterogeneity

when a mutation in any one of two or more genes can result in the same mutant phenotype

complementation test

a way to test if two mutations are from the same gene or different genes, two mutant strains with same mutant phenotype crossed, if all progeny wild type, complementation occurred and strains had mutations in different genes, if all progeny are mutants, no complementation occurred and strains had mutations in the same gene

penetrance

the fraction of individuals with a certain genotype that display that genotype’s characteristic phenotype

expressivity

the degree to which an affected individual displays the phenotype associated with that individual’s genotype, depends on factors such as environment, chance, alleles of other genes

mitosis

cell division where both the number and kinds of chromosomes are preserved, both daughter cells are genetically identical to the parent cell

cell cycle

a pattern of cell growth and division

G1

interphase, the gap before gene replication

G0 stage

when cells are not longer actively dividing

S phase

synthesis to replicate DNA of all chromosomes, uses the semiconservative method

G2

interphase, the gap before mitosis

M phase

mitotic phase, where the cell goes through the stages to separate DNA

prophase

where the chromosomes condense to form x-shaped chromosomes

sister chromatids

the replicated copies of a chromosome held together at the centromere

centromere

the area where two sister chromatids join together, is the tightest part of the chromosome, point of construction that binds proteins, primarily heterochromatin

centrosomes

move apart to opposite poles of the cell to form microtubules

chromosomes

thread-like structures made of protein and a single DNA molecule that carries genomic information from cell to cell

chromosome complement

complete set of chromosomes in plants and animals

diploid

cells with both copies of a homologous pair of chromosomes

homologous chromosomes (homologs)

chromosomes of the same shape, size and banding, have the same genes in the same order, one from each parent, carry different alleles

metacentric

when the centromere is near the center of the chromosome

acrocentric

when the centromere is near one of the ends of a chromosome, forming one long arm and one short arm

nonhomologous chromosomes

chromosomes that don’t match because they have different sets of genes

metaphase

the mitotic spindle begins to form, spindle fibers are attach to each chromosome at the kinetochore, chromosomes are moved to the metaphase plate