DNA structure Flashcards
Semester 1 year 1
Describe the structure of DNA nucleotides
-deoxyribose
-phosphate (usually 3 when in cell) on 5’ carbon
-base on 1’ carbon
What are the 2 types of base?
Purines - adenine and guanine (2 carbon rings)
Pyrimidines - cytosine and thymine (1 carbon ring)
Which bases pair together and how many bonds do they form?
A-T form 2 hydrogen bonds
G-C form 3 hydrogen bonds
How do 2 adjacent nucleotides join together?
OH group on 3’ carbon forms phosphodiester bond with phosphate on 5’ carbon of adjacent, releasing water
What was Chargaff’s’ experiment and what did he conclude?
-used paper chromatography to separate + isolate nucleobases components of DNA from different species
-compared ratios of the bases to each other
-%A=%T and %G=%C
-%AT=/=%CG
What were the conclusion from Wilkins and Franklin’s experiment?
-X pattern shows it has a helical structure
-regular pattern shows that it has a repeating, even structure
-distance between spots = distance of one turn
What are the main features of the Watson and Crick model?
-AT and GC H bonded base pairs
-antiparallel, complementary strands
-right handed double helix
-major + minor groove in DNA double helix
What are chromosomes?
Long DNA molecules with all or part of the genetic material of an organism
Describe eukaryotic chromosomes
-linear molecules held in the nucleus
-often have many chromosomes per genome
-contain centromeres + telomeres
What are centromeres and what do they do?
-specialised chromosomal region in which the structures that link to spindle microtubules assemble
-help chromosomes segregate at mitosis + meiosis
Describe how genetic material is found in prokaryotes
-bacteria generally have a single, circular chromosome
-plasmids are also often found (circular)
What are the roles of DNA binding proteins?
-regulate gene expression
-cut DNA at specific sequences
-protect DNA
Describe histones
-eukaryotic genomes are packaged into chromatin
-DNA wrapped around histone proteins
-not sequence specific
What are telomeres and what do they do?
-repetitive DNA at the ends of linear chromosomes
-protect the ends of linear chromosomes
Describe restriction endonucleases
-enzymes that cut DNA at specific (normally palindromic) sequences
-viral DNA is cut by enzyme but bacterial DNA is protected as it’s methylated
