genes and chromosomes (6.1, 6.2, 6.4) Flashcards
(21 cards)
what are genes?
genes are regions of DNA which contain instructions for building proteins. alternate forms of genes are called alleles
where is DNA in eukaryotic cells?
DNA is wrapped around proteins called histones
— can be bundled into coils to form chromatin fibres
where is DNA in prokaryotes?
prokaryotes contain small circular sections of DNA called plasmids
what is a genome?
a genome is a complete set of an organism’s hereditary information
who is gregor mendel?
he hypothesized the existence of a hereditary molecule passing information through the generations about 150 years ago
who is fredrick meisher?
he extracted an unknown substance from white blood cells
who is frederick griffith?
— studied two types of pneumonia
— concluded that an infectious strain could turn a non-infectious strain
— could not identify the material involved in that transformation
what is the chemical composition of DNA?
a nucleotide is made of:
- deoxyribose (a five carbon ring)
* the sugar in RNA is ribose
- a phosphate group links to the sugar and links it to another phosphate group, making it a polynucleotide
- has a nitrogenous base of: thymine (or uracil in RNA), adenine, cytosine, and guanine
which bases have double rings and which have single rings, and what are they classified as?
— double ring bases: adenine and guanine are purines
— single rings bases: cytosine, thymine, and uracil are pyrimidines
what is semi-conservative DNA replication?
the semi-conservative model states that each of the two parent strands of DNA are incorporated into a new double stranded DNA molecule
what is step one of strand separation?
— DNA is unzipped with enzyme: DNA helicase to break the h-bonds between base pairs starting with the replication origin
— point of separation of the strands is the DNA replication fork
— tension from unwinding strands are relieved by topoisomerases (enzymes that cleave one or two DNA strands and allow them to untwist and rejoin)
— strands are kept apart by single stranded binding proteins (SSBs)
— when helicase opens DNA, its copied in both directions and creates a replication bubble
— replication occurs everywhere, producing many replication bubbles
what is in step two, building complimentary strands?
— leading strand is built by DNA polymerase III by adding nucleotide triphosphates (a base with three phosphates and a sugar)
— new DNA is assembled from 5’ to 3’
when does replication begin?
— replication begins when RNA primase places a starting point, RNA primer about 10-60 nucleotides long
how many primers are needed for the leading strand to be built and in what direction?
one primer is needed for the leading strand, and it is built towards the replication fork.
in what direction is the lagging strand built and by what polymerase?
the lagging strand is built away from the replication fork in okazaki fragments by DNA polymerase III
what end are RNA primers added to the new strand?
— 5’ end of the new strand
— 3’ end of the parent strand
what does DNA polymerase I do?
DNA polymerase I removes RNA primers and replaces them with DNA nucleotides
how are okazaki fragments connected?
they are connected by DNA ligaments by creating phosphodiester bonds between nucleotides
what happens in step three, dealing with replication errors?
— DNA polymerase I and III proofread strands
— DNA polymerase II repairs damage to DNA
how does DNA replication work in prokaryotes
prokaryotic genomes are much smaller, containing usually only one replication bubble
how does DNA replication work in eukaryotes?
eukaryotic DNA is very long and linear, creating thousands of replication bubbles
