nucleic acids Flashcards
what are nucleic acids
organic compounds that include important macromolecules such as DNA
what does DNA contain
genetic material ( structural and functional role)
what is the thing that DNA is made of and thus this means it is…
its a polymer made up of NUCLEOTIDE MONOMERS thus its a POLYNUCLEOTIDE
what is a single nucleotide called
a mononucleotide
what are the 3 components that a nucleotide is made up of
-a phosphate group
-a pentose sugar (5 carbon sugar)
-a nitrogen containing organic base
DEFINITION: what is a nucleotide
A nucleotide is a molecule that is composed of a pentose sugar, a phosphate group and a nitrogen containing base. It is the monomer unit of nucleic acids.
In DNA what is the pentose sugar?
deoxyribose
In RNA what is the pentose sugar?
ribose
in DNA, what are the 4 organic bases?
Guanine
Adenine
Cytosine
Thymine
what are the two sectors organic bases can be classified as
Purine bases
Pyrimidine bases
what are Purine bases and examples
bases with two carbon rings (bigger)
G and A
what are Pyrimidine bases and examples
bases with one carbon base (smaller)
C and T
what forms when two mononucleotides join and what reaction allows this to occur
dinucleotide
-condensation reaction
where does the condensation reaction occur between mononucleotides, what bond does this create
between the hydroxyl group (-OH) on the phosphate group and pentose sugar, this creates a phosphodiester bond and forms a molecule of H2O
what does a series of condensation reactions form between multiple mononucleotides
a polynucleotide
DEFINITION: what is a polynucleotide
a polymer made up of many nucleotide monomers joined together by a series of condensation reactions
what breaks phosphodiester bonds
hydrolysis reaction ( addition of water needed)
describe the structure of DNA
double helix composed of 2 long polynucleotide chains.
The sides of the DNA double helicase are made from pentose sugar and phosphate groups forming a SUGAR-PHOSPHATE BACKBONE.(alternation of these units)
Two strands of DNA are held by hydrogen bonds between the bases.
The double helix of DNA= antiparallel- the strands of DNA run in opposite directions to each other
how many hydrogen bonds form between A and T
2
how many hydrogen bonds form between G and C
3
what will a larger purine always pair with?
a smaller pyrimidine
what dos it mean when DNA is stated as antiparallel
the two polynucleotide strands run in opposite directions
one of the strands run 5’ to 3’ while the other runs 3’ to 5’
how many polynucleotide strands does RNA consist of
1
what is the role of RNA
RNA acts as a messenger molecule- it helps transfer information from DNA to proteins
RNA also has roles in the regulation and synthesis of proteins
what are the nitrogen containing bases in RNA
adenine, guanine, cytosine and uracil
what type of base is uracil
pyrimidine base
outline the similarities and differences in RNA and DNA
RNA:
one strand
relatively short
ribose pentose sugar
G, A ,U, C
DNA:
two strands
very long
deoxyribose pentose sugar
G, A, T, C
during what phase does DNA replication occur
interphase ( S phase)
in eukaryotes, what is DNA stored in
long linear molecules called chromosomes
in prokaryotes, what is DNA found as
in long circular loop of DNA and smaller circles (plasmids)
what is DNA helicase
the enzyme that catalyses the breaking of hydrogen bonds between the complimentary organic bases in DNA
What is DNA polymerase
the enzyme that catalyses the synthesis of DNA by joining adjacent nucleotides , using the single stranded DNA as a template
DNA replication, describe the two strands in the replicated DNA
composed of one old strand and 1 new strand (semiconservative)
what is semiconservative replication
the method in which DNA replicates, creating two molecules of DNA that consist of one og DNA strand and one newly synthesised strand
what direction does DNA polymerase only move on new strands
5’ to 3’
-it works in both directions
DNA replication: what is the leading strand
the strand that is synthesised continuously following the movement of the replication fork
DNA replication: what is the lagging strand
the strand where the synthesis is discontinuous as DNA polymerase moves away from the fork, this is the lagging strand- areas are synthesised in short sections called okazaki fragments (fragments joined by the enzyme ligase)
what could be an error with DNA replication, what does this lead to
sometimes the wrong base pairs up during DNA replication -this happens randomly and spontaneously
this results in a change in base sequence in the newly copied DNA which is known as a mutation
functions of :
1-DNA polymerase
2-Ligase
3-Helicase
1-joins DNA back up hydrolysis and condensation) and catalysis of H-bonding
2-hydrolysis and condensation
3- unwinding DNA
what are genes
genes are sections of DNA that code for polypeptides and functional RNA
what is transcription? (simple)
transcription is the process of making messenger RNA from a DNA template
what is translation? (simple)
RNA molecules translated into a specific amino acid sequence
what is the genetic code?
The genetic code is the specific sequence of bases in DNA or RNA that codes for a sequence of amino acids during protein synthesis
4 features of genetic code
- its read in triplet code
- it is a degenerate code
- its a non overlapping code
- its universal
features of genetic code: degenerate def
an amino acid can be coded for by more than 1 group of bases
codon definition
a sequence of 3 bases of RNA that codes for a specific amino acid
how many codons are special and do not code for an amino acid
4 codons (1 start codon and 3 stop codons)
whqat dos the start codon code for?
the amino acid methionine
start codon sequence?
ATG
stop codon sequences?
TAG TAA TGA
How many combos does triplet code produce
64 combos
degeneracy means that amino acids can be made by multiple codons, why is this an advantage to organisms
degeneracy means that different codons can code for the same amino acid. This could be protective against mutations as there is a chance a codon could undergo a mutation (base substitution) to become another coding for the same amino acid (silent mutation)
describe the structure of mRNA
single stranded polynucleotide that coils into a single helix
mRNA length varies depending on the length of the gene transcribed
which strand of DNA contains the codons that are used to code for amino acids
the sense strand ( runs 5’ to 3’)
what strand of DNA acts as the template for transcription and what does this mean
the antisense strand so that the mRNA synthesised has the same sequence as the sense strand
describe transcription (6)
-in order for transcription to occur, the DNA double
helix must first be unzipped and H bonds broken.
- a gene unwinds and unzips
-the enzyme that catalyses this is called DNA helicase which moves along the sugar-phosphate backbone, beginning at the start codon
-this exposes a section of both coding sense strand and the template antisense strand
-the DNA antisense strand then acts as a template for the mRNA as free RNA nucleotides pair with the exposed complimentary bases.
-the RNA nucleotides are then joined to adjacent nucleotides by phosphodiester bonds to form the mRNA strand ( this reaction is catalysed by the enzyme RNA polymerase which travels along the sugar phosphate backbone in the 3’ to 5’ direction.
-when the transcription ends, the mRNA strand detaches from the DNA, allowing the double helix to reform. The mRNA contains codons ( groups of 3)
what does tRNA specify for
which amino acid is coded for by which specific triplet codon
talk abt the structure of tRNA
-a very short RNA molecule
-single stranded: can form complimentary base pairs with itself, folds into clover leaf shape
-one end of tRNA molecule extends out providing site for attachment for amino acids
-the opposite side of the tRNA contains the anticodon that is complimentary to a specific codon.
why can tRNAs with different anticodons bind to the same amino acid?
because code is degenerate
what are ribosomes the site of
site of translation
talk about structure of ribosomes
1 large subunit
1 small subunit
composed of 40% proteins and 60% RNA
-contains ribosomalRNA->(rRNA) (important for process of translation)
what does the rRNA in the large subunit act as and what does it do
it acts as a catalyst ( its an enzyme=(ribozyme)) and it catalyses the formation of peptide bonds as polypeptides are formed
describe the process of translation (6)
-the mRNA associates with a ribosome by binding to the small subunit at the start codon.
-the first tRNA molecule (carrying amino acid methionine) the binds to the start codon by H bonding, the tRNAs anticodon is complimentary to the mRNAS start codon.
-once the first tRNA has bound to the start codon, the large ribosomal subunit binds. The second tRNA binds which carries the specific amino acid coded for by the mRNA codon.
-the ribosome moves along the mRNA, it reads code
- a condensation reaction takes place, forming a peptide bond between the two amino acids, this then rereleases methionine from the first tRNA.
-The ribosome then moves forward 3 bases ( a codon) and the first tRNA is released.
-this process continues, extending the peptide by one amino acid each time, eventually a polypeptide is formed.
- Translations stop when the stop codon is reached, thsi codon has no complimentary tRNA. the subunits of the ribosome separate releasing the polypeptide.
What are base triplets in mRNA called!!!
codons
what is the sense strand
the sense strand is the coding strand which runs in a 5’ to 3’ direction
what is the antisense strand
the antisense strand is the non-coding strand running in a 3’ to 5’ direction
what are base triplets on DNA called!!!!
a triplet of bases
