DNA structure Flashcards
what is DNA made up of?
2 antiparallel polynucleotide chains
what are the 4 nucleotides subunits?
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine(C)
What are the key components of a nucleotide?
Phosphate group
Deoxyribose sugar
Nitrogenous base
Has 5’-3’ polarity
How many hydrogen bonds form between base pairs?
A-T pairs form 2 hydrogen bonds
G-C pairs form 3 hydrogen bonds
what are the 2 types of nucleotides
purines- 2 rings
pyrimidines - 1 ring
DNA is made of a nucleotide chain. what is the chain called?
deoxyribonucleic acid
how do nucleotides join together?
Phosphodiester bonds
what are adenine and guanine? why?
They are purines as they have a double ring structure (bigger than thymine and cytosine)
what are thymine and cytosine? why?
they are pyrimidines as they have a single ring structure (smaller than guanine and adenine)
why do G&C and T&A pair together?
Because a purine pairs with a pyrimidine. This means the distance between the sugar-phosphate backbone is constant down the DNA
what is the structure of DNA called?
Right handed double helix
what was Chargaff’s experiments in 1951?
-Used paper chromatography to separate and isolate nucleobases from DNA
-Analysed DNA samples from multiple species
-Led to key findings (Chargaff’s rules):
%A = %T and %G = %C
Total purines = total pyrimidines
AT/GC ratios vary between species
These findings were crucial for understanding DNA’s base-pairing structure and helped inform Watson and Crick’s later model of DNA.
what were Wilkins and Franklin looking at in 1952?
Looking at the structure of short pieces of DNA using X-ray crystallography
what did Wilkins and Franklin find after using x-ray crystallography?
X pattern= helix structure
Regular pattern= repeating and even structure
distance between the spots= distance of one turn
what did Watson and crick do with the info from Chargaff’s rule and x-ray crystallography?
A-T and G-C hydrogen-bonded base pairs
Antiparallel strands
Right-handed double helix
One helical turn every 10.5 base pairs
Major and minor grooves
what are chromosomes?
Linear molecules held in the nucleus that contain all or part of the genetic material. most eukaryotic chromosomes include packaging proteins called histones.
what is a centromere and its function?
Region within a chromosome that help chromosomes segregate (separate) at mitosis and meiosis
what is a telomere and its function?
Repetitive DNA at the ends of linear chromosomes. their function is to protect the ends of the chromosomes
What is the general structure of chromosomes and plasmids in bacteria?
Circular
what are the 3 roles of DNA binding proteins?
regulate gene expression
cut DNA at specific sequences
protect DNA
What is conjugation?
a method of genetic transfer between bacteria
what are transcriptional regulators?
proteins that bind regulatory sequences near to the promoters of genes to either stimulate or block transcription.
what is restriction endonucleases?
Enzymes that cut DNA at specific sequences
originated in bacteria to RESTRICT the action of viruses
