Who originally found DNA and what did he call it?
Friedrich Miescher in 1871. He called them nucleins
What is the Griffith Experiment (1928)?
The first demonstration of transformation of a specific genetic trait from one organism to another.
What did Avery, MacCarty & McLeod do in 1944?
They fractionated cell-free extraction of virulent pneumococcus and identified that DNA, not protein, caused transformation. First evidence that DNA carries genetic information.
What did Hershey and Chase do in 1951?
Sometimes called the "Waring Blender" experiment. They watched a T2 bacteriophage infect the bacteria Escherichia coli. DNA "has some function" as genetic material.
What kind of polarity does DNA have?
How are deoxyribose or ribose linked?
Via phosphate groups The 3'-OH of one group is linked to the 5'-OH of the next by a phosphodiester bridge. This is the backbone of DNA
Do bases project away from the backbone or toward the backbone?
Away from the backbone.
%G=%C, %A=%T i.e %purines=%pyrimidines ALWAYSSS!!!!
What did Franklin and Wilkins do in 1953?
Showed that DNA gave a characteristic X-ray diffraction pattern.
What was the pattern that was found of DNA?
Helical Comprised of two strands Has 2 periodicities along long axis (0.34nm and 3.4nm)
What did Watson and Crick do in 1953?
Developed a 3D model of DNA that was not fully accepted until 1960.
Are strands of DNA parallel or antiparallel?
Antiparallel that are said to be complementary to each other.
What are some other conformations the DNA molecule can adopt?
B form (right handed helix - main) Z form (left hand form) Cruciform (more exotic)
What can DNA triple helices possibly be used for?
A novel class of drugs designed to modify gene expression like oncogenes in cancer.
What does DNA's flexibility allow?
To be folded when being packed into the nucleus To wrap around proteins like histones
What type of coiled state is DNA in while in a cell?
A negative supercoil (underwound)
What two enzymes can modify supercoiling?
Topoisomerase I DNA Gyrase Helicases
What does Topoisomerase do?
Relaxes supercoiled DNA which is energetically favorable
What does DNA Gyrase do?
Converts relaxed DNA into negatively supercoiled DNA which requires ATP
What four antibiotics inhibits Bacterial DNA gyros?
Novobiocin Nalidixic acid Ciproflaxacin
What do helicases do?
Unwinds the two DNA strands which requires ATP to break hydrogen bonds
What happens when DNA is heated then cooled?
When heated it goes through denaturation which separates the strand then when it cools down the strands go through annealing thus reforming bonds between complementary strands
How many hydrogen bonds do GC and AT pairs contain?
GC = 3 bonds AT = 2 bonds The more GC content the higher the melting temperature of DNA
What is hypochromism?
When DNA strands are allowed to anneal, base stacking reduces UV absorbance
What is hyperchromism?
If helix is denatures, base stacking is destroyed resulting in UV absorbance going up
Define a gene.
Portion of a chromosome that determines phenotype Changes in gene alter phenotype
Who found the one gene-one enzyme hypothesis?
Garrod in 1909 when working on human alkaptonuria Genes work by controlling synthesis of specific enzymes
What did Sumner do in 1926?
Showed that enzymes are proteins
What did Beadle and Tatum do in 1941?
Working on mutants in mold Neurospora they found that each mutant lost one enzyme.
What is the physical template stand of a gene called?
The antisense strand
What is the non-template strand of a gene called?
Sense or coding strand/sequence
Does mRNA have the same sequence as the sense strand or the antisense strand?
The sense strand with the exception of using U instead of T
The total amount of DNA within a cell
What are some examples of extrachromosomal DNA?
Eukaryotic mitochondrial DNA
Does genome size correlate with species complexity?
Nope it does not
Describe bacterial chromosomes
Always double stranded (ds) DNA
Single, circular chromosome
Describe Extrachromosomal DNA (plasmids)
Always ds DNA, circular arrangement
Often carries genes for antibiotic resistance (R factors)
What are Eukaryotic genomes comprised of?
1) Chromosomal DNA - always linear ds DNA
2) Mitochondrial DNA - always circular ds DNA
Are the 22 pairs of autosomes numbered from largest to smallest or smallest to largest?
Largest to smallest
What is a Karyotype?
Cytogenic techniques use stains to identify banding patterns. Chromosomes are arrested in metaphase when they are duplicated and maximally condensed.
Classes of Short Interpersed Elements (SINES)
Satellite DNA - alpha satellites, mini satellies, Heterochromatin
What is Chromatin?
DNA + proteins
Why are proteins important in chromatin composition?
Critical for DNA compaction
How many types of histones (proteins) are there and are they basic or acidic?
5 types: H1, H2A, H2B, H3, and H4
Very Basic (lots of lys and arg)
What happens if the protein scaffold of chromatin is digested away?
What is the primary structure of DNA compaction?
How many bp's of DNA wrap around a histone octomer?
What is a nucleosome?
DNA + a histone core
What are nucleosomes connected by?
20-60 bp "linker" associated with histone H1
What do nucleosomes look like?
Beads on a string
Chromatids> Coil > Rosette > Loop > Solenoid (30nm fiber) > Nucleosome > Double helix
Start at double helix
What is the primary structure of compaction?
What is the secondary structure of compaction?
What is the tertiary structure of compaction?
Loop - primary form of chromatin found in interphase nucleus
What are the 3 specialized regions of chromosomes?
Origins of replication (ori)
What is the origin of replication?
Specific DNA sequence recognized by proteisn required for replication
What are telomeres?
Regions at the end of chromosome with many repetitive sequences that are no replicated during S-phase
How are the repetitive elements added to the end of replicated chromosomes?
By an enzyme called telomerase
What are the functions of Telomeres?
Seal chromosome ends to prevent fusion
Attach chromosome to nuclear envelope
What are centromeres?
Signle region of each chromosome that serves as an attachment point for proteins which link the chromosome to the mitotic spine.
What is the specific attachment region of the centromere called?
How are centromeres classified?
Submetacentric: slightly off center
Acrocentric: near one end
What are short arms of chromosomes called?
What are long arms of chromosomes called?
Which 5 chromosomes are condensed to form the nucleolus?
13, 14, 15, 21, 22