nucleic acids Flashcards
what structures are made from DNA?
chromosomes
what type of protein is contained in chromosomes?
histones
describe the structure of DNA?
- made from 2 polynucleotide molecules
- arranged in a double helix
what are the monomers of DNA and RNA?
nucleotides
what molecules are DNA and RNA made from?
- phosphate group
- (deoxy)ribose sugar
- nitrogenous bases
what reaction joins the components of a nucleotide together?
condensation
what are the four nitrogenous bases is DNA?
- adenine
- cytosine
- guanine
- thymine
what are the four nitrogenous bases in RNA?
- adenine
- uracil
- guanine
- cytosine
which nitrogenous bases are base pairs?
- adenine and thymine
- adenine and uracil
- guanine and cytosine
what is the bond between two nucleotides called?
phosphodiester bond
how is the double helix constructed in DNA?
- phosphate group in one nucleotide bonds with the pentose sugar from another via condensation reaction to form the backbone
- complimentary bases form the middle (ladder) via hydrogen bonds
how many hydrogen bonds form between base pairs?
- adenine + thymine/uracil : 2
- guanine + cytosine : 3
DNA is an antiparallel molecule. what does this mean?
the 2 polynucleotide strands are arranged in different directions
how does the structure of DNA make it a stable molecule?
- held together by phosphodiester bonds which are extremely strong, covalent bonds which arent easily broken
- thousands of hydrogen bonds between bases
how does the size of DNA help its function?
- DNA is a huge molecule
- this means it can carry the immense amount of genetic material it needs to
how does the structure of DNA ensure that the genetic material inside is protected?
- coiled into a double helix
- sugar-phosphate backbone
- means genetic information inside is protected from chemical and physical forces
what are the two main stages of cell division?
- nuclear divisions (mitosis or meiosis)
- cell division
describe the method of DNA replication
- DNA double helix is unwound partially by DNA helicase
- DNA exposed nucleotides are attached to new “free” complimentary nucleotides, using energy from the hydrolysis of ATP
- DNA polymerase attaches the new copy strand of DNA together with deoxyribose-phosphate bonds
what conditions must be met for DNA replication to take place?
- pool of “free” nucleotides containing all four types must be present
- both strands of DNA act as a template
- DNA helicase and polymerase must be present
- ATP must be present
what is semi-conservative DNA replicaion?
where there is one original strand of DNA that is being used as a template to create a new polynucleotide strand
describe the process of DNA replication in detail
- DNA helicase unwinds the double helix by breaking the hydrogen bonds between base pairs, exposing the nitrogenous bases
- hydrolysis of ATP activates free nucleotides
- activated nucleotides then attach themselves to their complimentary bases on the original DNA molecule
- new DNA molecule is built up
- DNA polymerase catalyses the condensation reactions between adjacent nucleotides, forming backbone
- “proof-reading” enzyme checks the new strand for mutations, then “winding” enzymes winds up the new copied polynucleotide chains to form a double helix
- genetically identical chains
summarise Meselson and Stahl’s experiment that provides proof for semi-conservative DNA replication
- grow bacteria in nitrogen 15 (heavier isotope); when centrifuged leaves “heavy DNA”
- transfer the cells into nitrogen 14 (lighter isotope) to grow for one gen; when centrifuged leaves a hybrid of heavy and light DNA
- leave to grow for a second gen, which when centrifuged leaves light and hybrid DNA
how does Meselson and Stahl’s experiment prove that DNA replication is semi-conservative?
- the new DNA has one strand of the old DNA and one strand of the new
- as more gens are produced, the DNA created is never purely one type (light or heavy) and there is always a mixture
what is ATP made up of?
- 3 phosphates
- adenine
- ribose
