lecture 19 Flashcards
what year did mendel do his experiment?
1865
what did mendel look at when obtaining results from his experiment with crossing peas?
phenotype
what are units of inheritance that mendel referred to?
genes
what is the first conclusion that medel made with his findings?
that characteristics of organisms are governed by units of inheritance or genes.
under the first conclusion made by mendel, what was the first reason for it?
each gene is controlled by two forms of a gene (one from mom and one from dad) called alleles
difference between genes and alleles?
genes specifies a trait (specific place in the dna sequence) and alleles specifies the form the gene takes. The gene could be eye color and the allele means blue, brown, or black.
under the first conclusion made by mendel, what was the second reason for it?
the two copies of the genes or alleles could be identical or nonidentical.
under the first conclusion made by mendel, what was the third reason for it?
when the alleles are nonidentical, the dominant allele is able to mask the recessive allele.
what is the second conclusion that mendel made with his findings?
a reproductive cell (sperm and egg= gamete) contains one gene (allele) per each trait
under the second conclusion made by mendel, what was the first reason for it?
somatic cells arise by the union of male and female gametes
under the second conclusion made by mendel, what was the second reason for it?
two alleles controlling each trait are inherited. one from each parent.
what is the third conclusion that mendel made with his findings?
the pairs of genes are separated or segregated during gamete formation or meiosis
what is the fourth conclusion that mendel made with his findings?
genes controlling different traits segregate independently of one another (law of independent assortment)
what is an example of the law of independent assortment?
the trait for flower color and flower position are independent of one another.
to sum it all up what did mendels work portray?
there were distinct traits passed on from parents to offspring and traits were inherited independent of one another.
what did mendels work not portray?
the physical nature of the genes and alleles and the locations of them within the organism.
what year did walther flemming do his experiments?
1880
what device did walther flemming use for his findings?
light microscope?
what did walther flemming find?
through light microscope images, flemming found cells do a lot to divide their nuclear contents equally between daughter cells (mitosis)
what did walther flemming observe about these “threads”
during mitosis, the nucleus became divided into these visible threads which were later named chromosomes or colored bodies.
what year did august weismann do his experiment?
1887
what did august weismann propose?
That there was is a stage called meiosis where chromosome number is reduced by half (reduction division) before gamete formation
what did august weismann observe through his experiment that backed up Mendel’s observations?
Each gamete only gets one allele per particular gene (second conclusion by mendel)
what year did theodore boveri do his experiments?
1889
what did theodore boveri find in his experiments?
theodore boveri studied sea urchin eggs that were fertilized by two sperms and found disrupted cell division and the early death of an embryo
what did theodore boveri find upon noticing a disruption of cell division and early death of an embryo in sea urchin eggs fertilized by two sperms?
Boveri was the first to find that there is a qualitative difference among chromosomes. The process of normal development depends upon a particular combination of chromosomes.
what do the qualitative differences if chromosomes discovered by boveri suggest?
That not all chromosomes are created equal. we need a specific number of chromosomes for an organism to continue to be alive.
Whose discovery did edouard van beneden back up?
Theodore boveri’s study.
what did edouard van beneden discover?
using ascaris or round worms, van beneden found that they had four large chromosomes. He also observed that gametes before fusion only had two chromosomes.
how did edouard van benden support the findings of mendel and august weismann?
mendel- the pairs of genes are segregated during gamete formation (meiosis) so that only one copy of a gene or allele is passed by each gamete.
weismann- during meiosis, the number of chromosomes reduced to half so that each gamete only gets one allele per particular gene.
how did edouard van beneden support the findings of theodore boveri?
A specific number of chromosomes are needed for proper development and function.
what did sutton present?
chromosomes are present as homologous chromosomes.
what are homologous chromosomes?
the mother and father homologous chromosomes joined during meiosis to form bivalents
what do homologous chromosomes do during meiosis
they pair up and separate into different cells.
what did sutton suggest with his grasshoppers having 8 homologous chromosomes that pair up during meiotic prophase to form bivalents?
- genes located on the same chromosome are usually inherited together and do not sort independently.
- If genes a part of the same linkage group, they will be inherited together. TRAITS THAT ARE CONNECTED TOGETHER IN LINKAGE GROUPS ARE LIKELY TO BE INHERITED TOGETHER.
How did sutton’s findings of homologous chromosmes back up mendels work?
- chromosomal behavior= genes that encode for different traits were on separate chromosomes, they would be inherited separate from one another.
- The traits that mendel observed were on separate chromosomes and that is why they were sorted independently.
what year did thomas hunt morgan do his experiment
early 1900s
what did thomas huunt morgan devleop with his study using drosophila melanogaster?
hunt morgan developed mutants with slightly different phenotypes than the parents. the parents were both wildtypes with normal characteristics found in the wild.
what is a mutation?
mechanism for which genetic variation can be introduced into populations
who was the first person to provide solid evidence that specific genes associate with specific chromosomes?
thomas hunt morgan
how was thomas hunt morgan able to determine that specific genes associate with specific chromosomes?
hunt morgan determined that there must be a specific gene that encodes for eye color and when it gets mutated, it changes the phenotype.
how are mutations created at a quicker rate than crossing over?
exposure to sub-lethal dose of xrays that can cause double strand breaks spontaneously.
what are polytene chromosomes
chromosomes in the cells of the salivary glands of drosophila flies. They go through repeated rounds of dna replication with no cell division.
what are polytene chromosomes used for?
polytene chromosomes are an easy way to determine how many genes are present in each chromosome and map the location of genes within chromosome. The thick bands are the loci of genes within the chromosome.
what are the “puffy” or thickened parts of the polytene chromosome?
parts of the dna where dna is being separated and transcribed.
How are polytene chromosomes visualized?
scanning electron microscopy
what image of a microscopy technique did watson and crick take from rosalind franklin to see that dna was in fact a double helix?
x-ray crystallography
what did the x-ray crystallography image tell us about the dna structure?
that dna was a double helix
what are dna?
they are the genetic material in all organisms.
what is the building block of a dna?
nucleotide
what three things are dna composed of?
deoxyribose sugar, phosphate, nitrogenous base
what are the two types of nitrogenous bases?
purines= adenine and guanine
pyrimidines= cytosine, thymine, (uracil is only in rna)
how many rings are in pyrimidines
one aromatic ring
how many rings are in purines
two aromatic ring
where is the phosphate attached
5’ of the sugar
where is the oh group attached
3’ of the sugar
where is the nitrogenous based attached
1’ of the sugar
why are nucleotides considered polarized?
they have different ends with different components. 5’ with the phosphate group and 3’ with the hydroxyl group attached to sugar
how are nucleotides linked?
by 3’,5’ phosphodiester bonds where the phosphate of one nucleotide on the 5’ end of the sugar is connected to the 3’ end of the sugar of a nucleotide on top of it.
where are nitrogenous bases facing in a dna strand?
they are facing outwards like stacked shelves
what does the 5’ and 3’ end of a dna strand look like?
5’ end has a free phosphate group. 3’ end has a free hydroxyl group.
what is one rule involving adenine by edwin chargaff?
adenine=thymine
what is one rule involving cytosine by edwin chargaff?
cytosine= guanine
in chargaffs rule, do all nitrogenous bases exist in an equal amount?
A+T does not equal G+C
what makes the outside of a dna helix?
the sugar phosphate backbone
what was one thing watson and crick proposed about the dna structure? (1)
dna is a double helix
what was one thing watson and crick proposed about the chains of dna? (2)
dna consisted of two chains of nucleotides that spiral around one another.
what was one thing watson and crick proposed about the polarity of a dna helix? (3)
the two chains are antiparallel and they run in opposite directions from one another. 5’ to 3’ is paired up with 3’ to 5’.
what was one thing watson and crick proposed about the inside and outside of a dna double helix?
the inside is composed of the nitrogenous bases and the outside is composed of the sugar phosphate backbone.
what is one thing watson and crick proposed that supported chargaffs observations?
The dna has A and t paired up as well as C and G paired up since they exist in equal amounts according to chargaff.
how are the two dna chains held together?
through hydrogen bonding of the nitrogenous bases
how many hydrogen bonds are there between each pairs of the adenine to thymine and cytosine to guanine? What takes more energy to break?
adenine and thymine have 2 hydrogen bonds. guanine and cytosine have 3 hydrogen bonds. guanine and cytosine take more energy to break since it has 3 h bonds.
how can the individual nucleotides be visualized?
through an electron density map created after x-ray crystallography of the dna.
what do you call it if the bases are paired with one another? a to t and g to c
complementary
what kind of turns and backbone configurations do dna have? what are they useful for?
major groove and minor groove. It is important for proteins to recognize specific regions of the DNA.
how many residues do dna take a turn?
10 residues
based on the structure of the dna by watson and crick, what observations can be made? 1/3
dna is used for the storage of genetic information. dna must contain info to assemble all proteins synthesized by organism.
based on the structure of the dna by watson and crick, what observations can be made? 2/3
replication and inheritance. dna replication allows the genetic instructions to be transmitted from one cell to its daughter cell and to offspring.
based on the structure of the dna by watson and crick, what observations can be made? 3/3
expression of the genetic message. the info in dna must be used to direct which specific amino acids are incorporatated into the polypeptide chain.
how is information stored within DNA?
through the specific order of the nucleotides that were added to the dna strand.
what corresponds to a gene?
a dna segment
what dictates the amino acid sequence?
the sequence of the nucleotide determines the sequence of amino acids in the polypeptide.
what happens during replication?
two strands are separated and h bonds are broken. these strands serve as a template for complementary strand assembly. two copies are created for daughter cells.
who identified the first nuclein?
friedrick miescher from white blood cell and salmon sperm
what is nuclein?
phosphorus rich protein found in nucleus of the cell
what did aaron levene propose
tetranucleotide theory that said repetition of four nucleotides werer too simple to be genetic material.
who made an experiment with pneumococcus bacteria?
fredrick griffith
what did fredrick griffith propose about the r strain and s strain of bacteria?
they are interconvertible
what is the s strain of pmeumococcus bacteria?
the live encapsulated form
what is the r strain of pneumococcus bacteria?
the non virulent uncapsulated forrm
how was the experiment carried out by fredrick griffith?
- the virulent s strain with the capsule was injected into a mouse and the nonvirulent r strain was also injected and the s strain injected mouse died.
- a heat killed s strain was injected into the mouse and the mouse lived
- the heat killed s strain and normal r strain were mixed and the mouse died
what did the results of fredrick griffith portray?
some living cells are pathogenic because of transformation where some genetic material has been passed from s strain to r strain to make it virulent.
what is transformation defined as? and who clearly supported this?
change in the genotype and phenotype due to the assimilation of foreign dna. avery, macleod, and mccarty.
what experiment solidified the fact that dna is the genetic material and not protein?
hershey and chase
what was step one of the hershey chase experiment?
the bacteriophage viruses were grown in radioactively labeled phosphorus(dna) and sulfur (protein) and bacteria cells were added
what was step two of the hershey chase experiment?
the mixture was blended to have viruses stop sticking to the bacterial cells
what was step three of the hershey chase experiment?
the bacterial cells were centrifuged and the pellet had the radioactively labeled phosphorus and in the other tube, phage protein that had radioactivity was found in the supernatant
what did the hershey chase experiment portray?
only dna was taken up by the bacterial cell and dna alone created new viruses.
what kind of microscopy will help us see a bacterial cell infected by a t4 bacteriophage?
electron micrograph
what is it called when dna has the normal 10 base pairs per turn?
having the normal 10 is in its relaxed state
what exactly is positive supercoiling?
when the right handed dna is twisted even tighter and the dna distorts and knots. even more compact. top strand moving towards right
what is negative supercoilling?
when the helix is twisted in the left handed fashion when unwinding dna. top strand goes to left
what helps us visualize the coiling of dna?
electron microscopy and gel electrophoresis
how does gel electrophoresis show supercoiling?
even though they are the same size, supercoiling causes dna to move faster through the gel because it is more compact.
what are enzymes that change the level of supercoiling called
topoisomerase
what does type i topoisomerase do?
changes the supercoiling by creating a transient break on one strand of duplex
what does type II topoisomerase do?
changed the supercoiling by creating transient breaks in both strands of the dna duplex
what does type II topoisomerase do?
changed the supercoiling by creating transient breaks in both strands of the dna duplex.it can also tie or untie knots
where do we find a lot of positive supercoiling?
right in front of the replication fork
how does topoisomerase II have to do with mitosis?
topoisomerase disentangles DNA molecules to be separated during mitosis
how do cancer drugs fight topoisomerase II
cancer drugs bind to the topoisomerase II enzyme and slows down the ability for the dna to replicate and divide. it prevents the cleaved dna strands from being released.
