year one revision Flashcards
what is a nucleoside?
base and sugar
what is a nucleotide?
nucleoside and phosphate group
DNA pentose sugar
deoxyribose
RNA pentose sugar
ribose
bases structure
consists of heterocyclic rings of carbon and nitrogen atoms.
DNA and RNA basic structure
phosphate - pentose sugar - nitrogenous base
how many rings do purines have?
two interlocked rings
how many rings do pyrimidines have?
single ring
which bases are purines?
adenine and guanine
which bases are pyrimidines?
cytosine, thymine and uracil
what are the common bases in DNA and RNA?
adenine, cytosine and guanine
what base is present in DNA but not RNA?
thymine
what base is present in RNA but not DNA?
uracil
what does uracil lack that is found in thymine?
5-methyl group
how is a base attached to a sugar?
covalently bonded by N-glycosidic bond
which form of DNA is most common?
B-DNA
A-DNA structure
right handed
pitch of 3.2nm
11 bases per turn
B-DNA structure
right handed
pitch of 3.4nm
10 bases per turn
Z-DNA structure
left handed
pitch of 4.5nm
12 bases per turn
codon definition
sequence of three nucleotides that correspond with a specific amino acid or stop signal
composition of bacterial genomes
single circular chromosome
considered haploid
plasmid definition
extra-chromosomal DNA, often found in the cytoplasm of a bacterial cell,which replicates independently
histone definition
small, basic proteins bound tightly to DNA
function of histones
structural support
involved in packaging
histone charge
positive
chromatin definition
DNA- protein complex
chromosome packaging at interphase
low packaging
what does first level of DNA packaging involve?
periodic coiling of the double helix around histone proteins
nucleosome definition
a length of DNA coiled around a core of histones
146 base pairs coiled arounf 8 histones
how are adjacent nucleosomes connected?
by linker DNA ( can be as long as 114bp)
histone H1 binds to linker DNA close to the nucleosome
euchromatin definition
loosely packaged DNA
can be transcribed
weak binding of histone H1
heterochromatin
tightly packaged DNA
cannot be transcribed
strong binding of histone H1
what must chromosomes conain in order to be copied and transmitted accurately?
a centromere
replication origins
telomeres
chromosome packaging during metaphase
highly packaged so they do not get tangled during cell division
linear size of chromosomes during metaphase
0.01% of the fully extended chromosomal DNA
what enzyme causes DNA strands to unwind?
DNA helicase
At what end are the nucleotides added the the DNA strand?
3’ end
what happens to deoxynucleoside triphosphates before they are added to the DNA strand?
DNA polymerase cleaves the precursors between the alpha and beta phosphate groups creating deoxynucleoside monophosphate that can be added
what does semi-conservative DNA replication mean?
each daughter duplex contains one strand from the original DNA duplex and one newly synthesised DNA strand
what is the direction of growth on the leading strand?
5’ to 3’
what is the direction of growth on the lagging strand?
3’ to 5’
what is the most common secondary structure of RNA in a cell?
hairpin
what does the hairpin RNA structure consist of?
stem and loop arrangement
RNA strand loops back and complementary bases pair forming the stem and leaves a small loop of unpaired bases
how much of the total cellular RNA does rRNA make up?
80%
what is rRNA
ribosomal RNA
what is tRNA
transfer RNA
acts as an adapter molecule between the nucleotide sequence of the mRNA molecule and amino acid
how much of the total cellular RNA does tRNA make up?`
15%
how is mRNA modified in eukaryotes?
addition of 5’ cap
addition of 3’ polyadenyl tail
introns spliced by spliceosomes. only after this happens can the mature mRNA leave the nucleus
why is a 5’ cap added to mRNA?
allows recognition by the ribosome
how is a 5’ cap added to mRNA?
add a G to 5’ end which is then methylated
why is a 3’ polyadenyl tail added to mRNA?
increases the half life and increases the efficiency of translation
what enzyme adds the 3’ polyadenyl to mRNA?
poly (A) polymerase
which RNA polymerase is responsible for transcribing all protein-coding genes in the nucleus?
RNA polymerase II
which DNA strand is used as a template during transcription?
antisense strand
what is the process of transcription?
DNA helicase unwinds the DNA locally as RNA polymerase advances
ribonucleoside triphosphate precursors are cleaved by the polymerase to form ribonucleoside monophosphates which are added on nucleotide as a time to the 3’ hydroxyl group of the previous nucleotide
what are transcription factors and what do they do?
proteins which bind to the promoter and position and guide the RNA polymerase to help transcription proceed effectively
what is the start codon?
AUG
what are the stop codons?
UAG
UAA
UGA
what is a point mutation
when a single base pair is altered
what are the types of point mutation
substitution
deletion
addition
what are the possible effects of point mutations
silent- no effect, the base change still encodes for the same amino acid
missense- the base change now encodes for a different amino acid
nonsense- the base change encodes for a stop codon
what is an open reading frame?
section of DNA between a start and stop codon that is able to be translated
no overlaps and no gaps
how many reading frames does double stranded DNA have?
6
what does cDNA stand for?
complementary DNA
what are exons?
protein coding regions
what are introns?
non protein coding regions
