Test 3 Flashcards
What are the 4 characteristics that genetic material must posses?
- Must contain complex information
- Must replicate faithfully
- Must encode the phenotype
- Must have the capacity to vary
What is meant by “must contain complex information”?
The genetic material must be capable of storing large amounts of information
• instructions for the traits and functions of an organism
What is meant by genetic material “must replicate faithfully”?
• At each cell division, genetic instructions must be accurately transmitted to replicated cells.
• When organisms reproduce and pass genes to their progeny, the genetic instructions must be copied faithfully
What is meant by genetic material must “encode the phenotype”?
• genetic material has to have capacity to be expressed a a phenotype
• the products of a gene is often a protein or RNA molecule, so there must be a mechanism for genetic instructions in DNA to be copied to RNAs and proteins
What is meant by genetic material must “have the capacity to vary”?
• there must be variation with different and within species
• they must differ in their genetic makeup
Why was the discovery of the structure of DNA so important for understanding genetics?
understanding how genetic info is encoded and expressed is IMPOSSIBLE without knowing the structure of DNA
What are nucleotides?
unit of DNA or RNA
What are nucleotides made of?
Sugar, phosphate and a base
What do Chargaffs rules state?
Adenine=thymine
Guanine=cytosine
What organism did Fred Griffith use in his experiments?
streptococcus pneumoniae TYPES II and III
bacterium that causes pneumonia
What are the variants of the polysaccharide capsule?
• Rough
• Smooth
What are the characteristics of the ROUGH (R) variant in S. pneumoniae?
• does not form a polysaccharide capsule
• non-virulent
• do not kill mice
What are the characteristics of the SMOOTH (S) variant in S. pneumoniae?
• forms a polysaccharide capsule
• virulent
• kills mice
How does the smooth variant kill mice?
Because the smooth capsule protects it from the immune system
What happened when Griffith injected heat-killed IIS bacteria?
• The mice would live
• no IIIS bacteria in their blood
What happened when Griffith injected living IIR bacteria and a large amount of heat-killed IIS bacteria?
The mice got pneumonia and died
• there was IIS bacteria in blood in the heart
What did Griffith conclude?
IIR bacteria transformed using the genetic virulence of dead IIS bacteria. This produced a permanent genetic change in the bacteria
What is the transforming principle?
DNA; which is the substance responsible for transformation
What did Avery, MacLeod, and McCarty’s experiment reveal?
That the transforming substance is DNA
How did Avery, MacLeod, and McCarty do their experiment?
- Isolated the transforming substance
- enzymes that break down proteins had NO effect on the transforming substance
- Ribonuclease that destroyed RNA, had no effect
- DNase destroyed the transforming substance
What is the conclusion of the Avery, MacLeod, and McCarty experiment?
DNA is the carrier of the information for the serotype (type) and capsule (rough or smooth) production
What is a T2 bacteriophage?
A virus that infects the bacterium E. coli
How does a a bacteriophage infect a bacterial cell?
- Attaches to the outer wall of bacterial cell
- Injects it’s DNA into cell
- Bacterial chromosome break down and phage chromosome replicate
- Replicates and directs cell to synthesize phage proteins
- Phage DNA becomes encapsulated within the phage proteins
- Produce phages that lyse (break open) the cell and escape
What was the purpose of Hershey and Chase experiment?
To determine if the phage protein or the phage DNA was transmitted in phage reproduction
Why did Hershey and Chase use isotopes in their experiment?
Used as a tracer to identify the location of a specific molecule. A molecule containing the isotope will be radioactive and easily detected
What did Hershey and Chase use to identify and follow phage DNA?
• 32P
• phosphorus isotope BECAUSE DNA contains phosphorus
What did Hershey and Chase use to identify and follow phage protein?
• 35S
• sulfur isotope because protein contains SULFUR
How did Hershey and Chase do their experiment?
- One batch contained E. Coli containing 35S and infect bacteria with T2 phage. All progeny phages would have proteins labeled w 35S
- Another batch of E. Coli in medium containing 32P and infected bacteria with T2 phage. All progeny phages would have DNA labeled with 32P
- Separate batches of unlabeled E. Coli were infected with 35S and 32P labeled progeny phages
- After time, they centrifuged the cells to separate proteins from cells
What was the result after centrifuging the 35S batch?
• 35S is recovered in the fluid containing the virus coats
• No radioactivity is detected
• protein was not transmitted to the progeny phages
What was the result after centrifuging the 32P batch?
• infected bacteria form a pellet containing 32P at the bottom of tube
• progeny phages are radioactive indicating that DNA was transmitted to progeny phages
How did Rosalind Franklin and Wilkins use X-ray diffraction to study DNA?
- Crystals of a substance are bombarded with X-rays, which are diffracted (bounce off)
- The spacing of the atoms within the crystal determines the diffraction pattern, which appears as spots on a photographic film
- The diffraction pattern provides information about the structure of the molecule
How did Watson and Crick create the structure of DNA?
• used Rosalind’s X-ray diffraction images
• applied the laws of structural chemistry
• used Chargaff’s base ratios
What did Watson and Crick’s model show?
• DNA consists of two strands of nucleotides that run in opposite directions
• strands winds around each other to for right-handed helix
• sugars and phosphates on the outside
• bases in the interior
What was the purpose of Fraenkel-Conrat and Singer’s experiment?
To figure out if RNA or protein Carrie’s the genetic material in tobacco mosaic virus (TMV)
How did Fraenkel-Conrat and Singer do their experiment?
- Degraded both types (A and B) of TMV to get RNA and coat proteins
- Mix RNA of one type with protein of other type (Type A RNA + type B protein)
- Created hybrid viruses
- Infect tobacco with the hybrids
- New viral particles were produced
- New viral progeny were identical to the strain from which the RNA had been isolated and didn’t show strain that donated the protein
What was the conclusion of Fraenkel-Conrat and Singer’s experiment?
That RNA directs coat protein synthesis
What did Gierer and Schramm demostrate?
RNA isolated from TMV is sufficient to infect tabacco plants and direct the production of new TMV particles
What did Gierer and Schramm confirm?
That RNA carries that genetic information in the virus
What are the sugars of nucleic acids?
Pentose sugars
How many carbons do pentose sugars have?
5
1’, 2’, 3’, 4’, 5’
What is the sugar in RNA?
Ribose
What does the ribose have attached at the 2’-carbon?
OH
What is DNA’s sugar?
DEOXYribose
What does the deoxyribose have attached at the 2’-carbon?
One Hydrogen atom
overall contains one oxygen fewer
What are the types of nitrogenous bases?
Purine and pyrimidine
What does a purine consist of?
A six-member ring attached to a five-member ring
What does a pyrimidine consist of?
A six-member ring
What are the two purines?
Adenine and Guanine
What are the three pyrimidines?
Cytosine, thymine, and uracil
Which purines are present in DNA?
Both, adenine and guanine
Which purines are present in RNA?
Both, Adenine and guanine
Which pyrimidines are present in DNA?
Only cytosine and thymine
Which pyrimidines are present in RNA?
Only cytosine and Uracil
What is a phosphate group?
A phosphorus atom bonded to 4 oxygen atom
How do phosphates of nuleic acids respond in near-neutral solvents?
Tend to lose H+
Where is the phosphate group bonded to on a nucleotide?
To the 5’-carbon of the sugar (ribose or deoxyribose)
Where do the nitrogenous bases attach to on the sugar?
1’carbon of the sugar
What are DNA nucleotides called?
Deoxyribonucleotides
What are RNA nucleotides called?
Ribonucleotides
How are the sugars in RNA and DNA different?
The sugar inRNA has a hydroxyl group (-OH)
What is a polynucleotide strand?
Series of nucleotides linked together by phosphodiester bonds
What is the backbone of the polynucleotide strand composed of?
Alternating sugars and phosphate groups
How are the complementary bases connected between antiparallel strands?
Paired through hydrogen bonding
What does the DNA 3’ end consist of?
A hydroxyl group attached to the 3’-carbon of the sugar
How are DNA nucleotides joined into polynucleotide strands?
By phosphodiester bonds connect the 3’-carbon atom of one nucleotide to the 5’-phosphate group to the next
What bonds connect sugars and phosphate groups on the same strand?
Covalent phosphodiester bonds
What is the B form DNA structure?
• most common
• most stable
• right-handed helix
• plenty of water surrounds the molecule
• No unusual base sequences in DNA
How many base pairs are in each rotation?
10 base pairs (3.4nm)
What is the A form DNA?
• exists if less water is present
• right-handed helix
• shorter and wider
• more turns per distance
What is the Z form DNA?
• left-handed helix
• sugar-phosphate backbone zigzags back and forth
What is the central dogma?
How genetic info passes from DNA to protein in a one-way information pathway
What are the steps of the central dogma?
• DNA replication
• Transcription
• translation
What is replication?
Information passes from one DNA molecule to other DNA molecules
What happens in transcription?
Information passes from DNA to RNA
What happens in translation?
Information passes from RNA to protein
What is reverse transcription?
Synthesis of DNA from an RNA template
What is a hairpin structure?
• when sequences of nucleotides on the same strand are complementary and pair with each other
What is DNA methylation?
when methyl groups are added by enzymes to certain positions on the nitrogenous bases
What is supercoiling?
Super twisting was a cell compacts DNA
What is positive supercoiling?
• Overrated DNA
• helix supercoils and twists on itself
What is negative supercoiling?
• underrotated molecule
• twists on itself in OPPOSITE direction
What are looped domains?
when DNA is arranged in looped structures and supercoiling will take place within the loops
What is chromatin?
Complex of DNA and proteins
What are histones?
•proteins in chromatin
•holds DNA in contact
What is formed when DNA is complexed with histones?
Nucleosomes
What does each nucleosome contain?
8 histone proteins around
• 2 copies of each of the core histones
What are the four core histones?
H2A, H2B, H3, H4
How to histones interact with the DNA strand?
• positively charge amino acid histone tails INTERACT with negative charge of phosphate on DNA
• keep DNA and histones tightly packed
What does the H1 histone do?
• Binds to 20-22 bp of DNA where DNA joins
• leaves the histone octamer
• helps lock the DNA into place
•clam around the nucleosome”
What is linker DNA?
the region of DNA that separates two nucleosomes
What is the 10nm chromatin fiber?
Lowest level of chromatin structure
• 147-147 bp
• wrapped around histones 1.66 times
What is the 30 nm chromatin fiber?
• when the the 10nm fiber bundled and condenses
• H1 binds the nucleosome and linker DNA together
• reduces the length of DNA by pulling everything together
What are Chromosome Scaffolds?
• non histone structural proteins
• 30 nm chromatin fiber emerge in 300 nm loops held by scaffold associated regions (SARs)
• reduces DNA length 10^4 times
• increases width 350-400 times
Why are chromosome scaffolds useful?
Leaves DNA more accessible when expression is needed
What is euchromatin?
• condenses and decondenses regionally or regularly
• active gene expression
• where most transcription takes place
What is heterochromatin?
• highly packed regions of chromosomes
• Doesn’t open up
• fewer active genes
• repetitive sequences
• replicate late in S-phase
What is CONSTITUTIVE herterochromatin?
• permanent heterochromatin
• found at centromeres and telomeres
What is FACULTATIVE heterochromatin?
• occur during developmental stages
• these DNA regions can go between heterochromatin and euchromatin at times
What does DNase I do?
Break the sugar phosphate backbone’s covalent bonds
What is the relationship between condensed DNA and DNase I?
condensed DNA is bound tightly to proteins and leaves little accessibility to DNase I
What is the relationship between decondensed DNA and DNase I?
decondensed DNA, 10 nm fiber, and loosely bound DNA in nucleosomes is SUSCEPTIBLE to break by DNase I
What is the DNA sequences of centromeres like?
They vary widely from species to species
• vary in sequence and length
What are common structural features in centromeric chromatin?
• heterochromatin (highly condensed)
• in nucleosomes, special histone takes H3 place called CENP-A
• interact with kinetochore proteins
What does the kinetochore do?
Attached the chromosome to the spindle microtubules
What are characteristics of telomeres?
• many units of adenine or thymine, followed by guanine units
• tandemly-repeated sequences
• G-rich stand creates a short region of single stranded DNA at the very 3’ end
What is a triple-stranded t-loop?
• When the G-rich strand folds over and pairs with a short stretch of DNA
• forms a t-loop
• is a protective structure
What is shelterin?
multipurpose complex that binds to telomeres and protects the end of DNA from being repaid as a double-stranded break in DNA
What is unique-sequence DNA?
sequences that are present only once or a few times in the genome
• encode proteins for most of the genes
What is repetitive-sequence DNA?
exists in many copies
What is moderately repetitive DNA?
• 150-300 bp long
• repeated thousands of times
What are interspersed repeats?
Repeated sequences that are scattered throughout the genome
What are short interspersed elements (SINEs)?
• many short repeats
• Alu sequence
What is Alu sequence?
• 300 bp
• present more than a million times
• 11% of human genome
• no obvious cellular function
What are long interspersed elements (LINEs)?
• consist of several thousand base pairs
What is HIGHLY repetitive DNA?
• short sequences
• ~ or > 10 bp
• repeated in tandem and clustered in certain regions of chromosome
• aka satellite DNA
• no known function
What is satellite DNA?
• aka highly repetitive DNA
• proportions of four bases differ from other DNA sequences
• separates as a satellite fraction when centrifuged
