TBL 3 - DNA Flashcards
What is DNA composed of and what does it carry?
DNA is a polymer composed of 2 polynucleotide chains that coil around each other to form a double helix.
Carriers genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.
What are 2 DNA stands know as and what is units are they composed of?
2 DNA strands are known as polynucleotides as they are composed simpler monomeric units called nucleotides.
What are the 4 nitrogen-containing nucleotide known as?
Each nucleotide is composed of 4 nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group.
What are the 3 parts that make up nucleotides?
Nucleotides form the basic structural unit of DNA.
- Nucleotides made up of 3 parts:
1) Deoxyribose (5’ C sugar)
2) Phosphate group
3) Cyclic amine (nitrogenous base)
What are the bonds used to join one nucleotide to the other?
Nucleotides joined to one another in a chain by covalent bonds (known as the phospho-diester linkage) between the sugar of one nucleotide and the phosphate of the next, resulting in alternating sugar-phosphate backbone.
How are nitrogenous bases bound together?
Nitrogenous bases of the 2 separate polynucleotide strands are bound together, according to base pairing rules (A with T, C with G) with hydrogen bonds to make double-stranded DNA.
In what direction do the strands run?
Strands are antiparallel run in opposite directions. One runs 3’ to 5’ the other runs 5’ to 3’.
How do DNA strands run in antiparallel and what is its purpose of it?
Done by sugar phosphate backbone twisting around itself in a coil.
Purpose of twisting to protect the bases inside it and prevent them from being damaged by environment.
What are the 4 nucleotides called? And what replaces thymine during RNA?
- A = Adenine
- T = Thymine
- G = Guanine
- C = Cytosine
RNA only: U= Uracil (replaces T)
What bond is used to hold bases?
Bases of one strand pair up with bases of another strand by hydrogen bonds.
Which bases are purine and which bases a pyrimidine?
Purine:
- Adenine
- Guanine
Pyrimidine:
- Thymine
- Cytosine
A purine must be base paired to a pyrimidine so what are A, T , G and C paired with and how much hydrogen bonds are between each pair?
A purine must always be base paired to a pyrimidine:
- A pairs with T (2 hydrogen bonds)
- G pairs with C (3 hydrogen bonds)
What does complementary mean?
Complementary: when you read the message on the one strand you automictically know the message on the other strand. NOT IDENTICAL but exact same message on both strands.
What did Rosalind franklin find out about DNA?
- 1953
- Crystallized DNA and x-ray diffraction
- It was clear that DNA was in a helix with symmetrically organized bases in centre
What did Watson and Crick suggest about DNA and what is there molecular model of DNA based on?
DNA is a double helix:
- James Watson and Francis Crick (1953) suggested double-helix model of DNA structure.
- Their molecular model of DNA was based on (a) X-ray diffraction image taken by Rosalind Franklin, Maurice Wilkins and Raymond Gosling and (b) the complementary base pairing in DNA.
Who discovered complementary base pairing and what did they discover and observe?
Complementary base pairing:
- 1950: Erwin Chargaff
- Erwin Chargaff discovered that the percentages of adenine (A) and thymine (T) bases are always equal in any sample of DNA
- Same thing true for other 2 nucleotides as well, guanine (G) and cytosine ( C)
- Observation that A = T and G = C became known as one of ‘Chargaff rules’
What is a chromosome?
Chromosome: a thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
What does eukaryotic chromosome consist of?
Each eukaryotic chromosome consists of long linear DNA molecule associated with proteins, forming a compact complex of proteins and DNA called CHROMATIN.
