DLA 1.1 DNA Structure And Analysis Flashcards
Give a brief overview of the scientific community realizing that DNA is the genetic material of heredity
Two major classes of molecules in the cell: nuclei can acid and proteins
By the end of the 1950s, much scientific evidence using bacteria, bacteriophages and radioactively labelled DNA and proteins demonstrated that nucleic acid is the genetic material
Discuss DNA being mutated by UV light
- DNA can be mutated if exposed to UV light at 260 nm
- Cataracts and cancer are caused
—Scurntusts used this to study bacteria and yeast
Discuss early scientists differentiating DNA and proteins
Both are colorless
-early scientists could be distinguish DNA from protein using a sample in a cuvette in a spectrophotometer and the correct wavelength of ultraviolet light
Discuss the difference in absorption of UV light between DNA and proteins
Nucleic acid absorbs UV light at 260nm and protein absorbs UV light at 280 nm
What are Mendel’s unit factors?
Now called genes
List the 4 criteria for genetic Material
- Replication
- Storage information
- Expression of information
- Variation by mutation
What is Replication?
Genetic material duplicates and then partitions into two daughter cells
What is storage of information ? (Criteria or genetic material )
- Genetic material is a repository of information that may or may not be expressed in the cell
- A chemical language for the survival of the cell
What is the expression of information criteria of genetic information?
- A cell needs to turn genes on and turn genes off
- Depends on the needs of the cell at any given time
Explain the Variation by mutation of genetic material criteria of genetic material
-A change in the chemical composition of the DNA that affects the expressed product of DNA
Assess the similarities and differences of a Nycoeic acids of RNA and DNA
- Both consist of nitrogenous bases with a pentose sugar to form a nucleotide
- Both Nucleosides join with phosphate groups to form a nucleotide
- Nucleotides join together to form polynucleotides through phosphate groups
- DNA uses thymine whereas Uracil is used by RNA
What are pyrimidines?
Pyrimidine rings are 6-membered single ring
Give 3 examples of pyrimidines
Cytosine and thymine and uracil
What are purines?
Purine rings are 9 membered rings(6 membered rings with five membered rings attached)
Give 2 examples of purines
Pure as gold- guanine and adenine
How is uracil chemically different to thymine?
Thymine has a methyl group at carbon -5 while uracil has an H
Where does the pentose sugar accept the nitrogenous base?
Carbon q
How can ribose and deoxyribose sugar be differentiated?
C2’: If it has OH here it is called ribose and for RNA
If it has H instead of OH, it’s called “deoxyribose” and used for DNA
Which carbons in the pentose sugar are used to make bonds for polynucleotides?
C3 and C5
What kind of bond forms between ribose/deoxyribose and nitrogenous bases?
A glycosidic bond
List the ribonucieosides
Adenosine
Cytidine
Guanosine
Uridine
List the deoxyribonucleosides
Deoxyadenosine
Deoxycytidine
Deixyguanosine
Deoxythymidine
What is a nucleotide?
When at least one(up to 3) phosphate groups are connected to the 5’ Carbon of the pentose sugar
What is the importance to phosphate groups in making DNA and RNA?
They store energy to help drive the synthesis of DNA and RNA
-form the structural backbone of DNA and RNA
Why are nucleoside triphosphates important to forking DNA and RNA?
- Have large amounts of energy due to delocalised electrons that is released when you break bonds between the groups
- This energy is used to drive the synthesis reaction, making polynucleotides
Two nucleotides joined together is a …
Dinucleotide
Three nucleotides joined together is a…
Trinucleotides
What is an oligonucleotide?
When up to 30 nucleotides are joined together
What are polynucleotides?
More than 30 nucleotides joined together
What is chromatography?
A technique to separate a mixture of compounds according to properties of molecules, could be size or charge
How did Chargaff isolate DNA?
- broke up the DNA into its individual bases with acid
- separated the 4 different bases from each other by chromatography
- calculated the amounts of each of the bases using spectroscopy (absorption is related to concentration )
What were Chargaff’s rule?
Base ratio of A to T was 1( equal amounts )
Base ratio of G to C was 1( equal ratio)
-Specific to the organisms
The combined base ratio were different and specific to the species (AT to CG ratio differ among species)
Who was Rosalind Franklin?
An expert x-ray crystallographer and one of the few people in the world at the time who could form proper crystals of DNA
She took the most important picture(picture 51) to show that DNA was helical
How did Maurice Wilkins try to take credit of R. Franklin’s discovery and show it to Watson and Crick ?
Maurice Wilkins didn’t accept R. Franklin was writing the results of her book/scientific periodical “nature”
Maurice Wilkins broke into her lab and showed picture 51 to Watson and Crick
Who was Raymomd Gosling?
The graduate student who took picture 51
Distinguish Rosalind Franklin as her contributions via Making Crystals of DNA
R. Franklin could make crystals of DNA using a variety of salt solutions with precise amounts of water, which range from wet to dry
Thus generate only the A forms or only B forms via hydrating and dehydrating under hydrogen gas
She then pulled the crystals into a single fibers for x-ray use
She used a tilting microfocus camera and developed a technique for improving the orientation of her DNA fibers so that the beams of X-ray took clear pictures DNA at different hydration’s
How did R. Franklin know phosphates were outside the DNA?
- based on the way DNA took up water, Franklin suggested that the phosphates (hydrophilic) must be in the outside of the helix
- DNA strands are anti parallel
Differentiate A form and B form DNA in shape and size
Overall- A form DNA is short and broad while B form is long and thin
Diameter- 25.5 A in A form while 23.7 A in B form
Differentiate in terms of rise per base pair between A form and B form of DNA
2.3 A in A form whereas 3.4 A in B form
Differentiate base pairs per helix between A form and B form of DNA
11 base pairs per helix in the A form while there are 10 base pairs per helix in the B form
Differentiate, using the direction of the helix between A form and B form of DNA
A form- Right handed(clockwise)
B form- right handed(clockwise)
How did Watson and Crick build a model of DNA
Watson and Crick collected information from Chargaff, a Franklin, Linus Pauling (who proposed a triple helix with the phosphates inside)
Built a model and published in Nature, 1953, in the same edition that Rosalind Franklin published her photograph 51 with Raymond Gosling aa’s co-author
-Nobel prize was given to Watson, Crick and Wilkins in 1962
When did Rosalind Franklin die of ovarian cancer?
On April 16, 1958
Why wasn’t Rosalind Franklin awarded the Nobel prize after her death?
Nobel prizes are not awarded to those who have died (posthumously)
Describe the structure of form B DNA
Two long polynucleotide chains coiled around a central axis forming a right handed double helix
- nitrogenous bases stacked in the center
- the 2 chains are anti-parallel
- each complete turn of the helix is 34A
- the larger major groove alternates with a smaller minor groove which winds along the length of the molecule:
- Major groove is 22A
- Minor groove is 12A
Between major and minor grooves in B form DNA , which is be translated for enzymes?
Major grooves- it gives more space
When was Z form DNA discovered?
In 1979
Describe Z form DNA
Rarely seen, usually important for gene regulation
Is a left handed double helix
Base pairing only works if …
Nitrogenous bases of the two chains are in anti-parallel
Why is DNA double helix very stable?
Thousands of bonds between base pairs
Why are phosphate groups on the outside while the nitrogenous bases on the inside
Because phosphate groups are hydrophilic while nitrogenous bases are hydrophobic
This privudes more stability to the double helix
What RNA is double stranded?
Animal viruses can have double stranded RNA
How does RNA approve its stability?
Single stranded RNA is not very stable in the cytosol, so it forms a secondary structure where it folds back on itself to form short regions of complementary base pairing
Also called stem-loop or hairpin structures
What are the 3 major classes of RNA?
mRNA
tRNA
rRNA
What are the unique RNAs in Eukaryotes
- Telomerase RNA
- RNA primers
- snRNA
- Antisense RNA, micro RNA and siRNA
What is the function of telomerase RNA?
Involved in DNA replication at the chromosome ends
What are RNA primers?
Involved in starting off DNA synthesis
What are snRNA?
Small nuclear RNA which helps process mRNA
What are the functions of Antisense RNA, micro RNA and siRNA?
Involved in gene regulation
Identify all the names of secondary structures for RNA, (comeback and find these on diagrams
Hairpin loop
Bulge loop
Multi loop with 3 branches
Pseudoknot
Stem
Give a major technique used to analyze DNA
- DNA is absorbs UV light at 260nm , when heated, DNA becomes denatured and unwind
- during unwinding, the viscosity of DNA decreases and the absorbance increases, called the hyperchromic shift
- A melting profile is plotted against temperature and you get a melting curve
- The midpoint of the curve is called a melting temperature( Tm) where 50% of the strands have unwound
How can Tm/ melting temperature of DNA indicate information its base pairs?
molecules with hugher Tm, have more G-C content
Molecules with lower Tm, have a higher A-T content
How can electrophoresis be used to study DNA?
- separates size fragments of DNA and RNA
- Nucleic acids are negatively charged due to phosphate bonds
- DNA or RNA sample placed into a semi solid gel immersed in a solution that conducts electricity
- A current is run through the gel and solution
- Molecules migrate to the positive pole
- Small molecules can migrate through the semisolid gel faster than longer molecules
