21 DNA as genetic material Flashcards
What is the central dogma of biology?
DNA -> RNA -> protein
what is genetic material?
a “transforming principle” in one strain, can cause heritable change in another strain of cells
How did Griffith’s experiment discover the transforming principle?
- used S (smooth strain, virulent) and R (rough strain, non virulent)
- either inject IIIS or IIR bacteria into a mouse
- type IIIS (virulent) bacteria in mouse = death, tpye IIIS (virulent) bacteria recovered
- type IIR (nonvirulent) bacteria into mouse = lives, no bacteria recovered
- heat killed type IIIS (virulent) bacteria into mouse = lives, no bacteria recovered
- a mixture of type IIR bacteria and heat-killed type IIIS bacteria in mouse = dies, type IIIS (virulent) bacteria recovered
a substance in the heat-killed virulent IIIS bacteria genetically transformed the type IIR bacteria into live, virulent type IIIS bacteria
something in IIIS transformed IIR into IIIS
How did Avery, Macleod, and McCarty’s experiment discover that its DNA that is the transforming principle?
- added either RNase (destorys RNA), Protease (proteins), or DNase (DNA) to IIIS bacterial filtrate
- then added to type IIR bacteria
- DNase one found only type IIR bacteria
- RNase and Protease found both type IIIS and type IIR bacteria
Only DNase destroyed the transforming principle: DNA is the transforming principle
What is the life cycle of T2 phages like?
- inject either DNA or protein into a cell, and reproduce there, and burst out
- enters a bacterial cell to direct the assembly of new viruses
How did Hershey-Chase experiment showed that DNA is the genetic material?
- either DNA or protein is the hereditary material that enters a bacterial cell to direct the assembly of new viruses
- labelled bacteriophage proteins with 35S, or DNA with 32P
- placed each in their own test tube with bacteria
- blended and centrifuged to seperate the phage from the bacteria
- radioactivity was measured in the pellet and supernatant
- found radioactive pellet with 32P labeled phage = DNA is in the bacteria
- found radioactive supernatant fluid with 35S labeled phage = protein is outside of cell
DNA, not protein enters bacterial cells and directs the assembly of new viruses
How did Fraenkel-conrat and singer’s virus reconstitution experiment show that RNA in TMV carries the genetic info?
- some virus dont have DNA so they must have something else - RNA
- What substance RNA or protein carries the genetic material in tobacco mosiac virus (TMV)
- degrade both types of TMV into RNA and coat proteins and switches them around, type A RNA + type B coat protein etc
- creates hybrid viruses
- infect tobacco with the hybridds
- then found the type of RNA in the hybrid parent TMV determines the RNA and protein of the progeny viruses
RNA is the genetic material of TMV, Nucleic acid is the transforming principle
Type A RNA and Type B protein infect tobacco -> find type A rna and protein in tobacco
What is the structure of nucleotides?
- pentose sugar
- phosphate group
- nitrogen-containing base
what is the polymer of nucleotides?
nycleic acids
How does RNA and DNA pentose sugar differ?
on less oxygen on C2 in DNA
What is C1 of pentose sugar attached to?
purine or pyramidine base
What are the 2 types of nitrogenous bases?
Purine: A and G
Pyrimidine: C, T and U
Purine has 2 rings
which parts of the purine and pyrimidine are attached to C1 of sugar?
N-9 for purine
N-1 for pyrimidine
What are the names of the nucleotides in DNA?
A = dAMP
G = dGMP
T = dTMP
C = dCMP
deoxycytidine 5’-monophosphate
deoxythymidine 5’-monophosphate
deoxyadenosine 5’-monophosphate
deoxyguanosine 5’-monophosphate
How are nucleotides joint tgt by?
phosphodiester bonds
phosphate group connect to the 3C of one sugar, and the 5C of the next sugar
What is the backbone of nucleic acids made up of?
alternating pentose and phosphates
what are the 2 ends of nucleic acid strands?
5’ and 3’ end
What is chargaff’s rule on DNA?
in DNA from many diff species: amount of A=T, amount of G=C
What did Rosalind Franklin and Maurice Wilkins use and find?
used xray diffraction to analyze DNA fibers, and deducted that DNA molecules are helical
What did Francis Crick and James Watson do?
used model building and combined all the knowledge of DNA to determine its structure
What are 6 key features of DNA?
- right handed double stranded helix, uniform diameter
- antiparallel: 2 strands run in opposite directions
- 5’ phosphate group and 3’ hydroxyl group
- complementary base pairing (A-T, G-C)
- bases are exposed in the major and minor groooves, can interact with proteins
- B-DNA (watson and crick form) consists of an double helix with approx 10 bases per turn
How many H bond between A-T and G-C?
A-T = 2
G-C = 3
The major and minor groove sides (image)
What different forms can DNA assume? L or R handed?
B-DNA - most common in cells (~10bp/turn)
A-DNA - more compact (~11bp/turn)
Z-DNA - form under high salt condition or special base seuqnece (12bp/turn)
A and B-DNA - right handed helix
Z-DNA - left handed helix
What is the hairpin structure in DNA and RNA?
hairpin structure: in single strands of nucleotides, when sequences of nucleotides on the same strand are inverted complements, a hairpin structure will be formed
What is the cruciform DNA structure?
2 hairpin structure back to back
How can DNA form triplex structures?
hoogsteen base pairing
How can DNA form quadruplex structures?
- with 1, 2, or 4 G-rich strands
- found in telomeres (G-rich repeats) at the ends of chromosomes and promotors that contain a polypurine-rich (rich in purine) strand
What are the potential functions of quadruplex structures?
- DNA replication control:
- Transcriptional control
