nucleic acids Flashcards
what are nucleic acids ?
large molecules found in cell nuclei
what are the 2 types of nucleic acids ?
DNA
RNA
what is the overall roles of RNA and DNA ?
storage and transfer roles of genetic information
the synthesis of polypeptides
what is the overall structure of nucleic acids ?
- contain carbon hydrogen oxygen nitrogen and phosphorus
- large polymers formed from nucleotides linked together in a chain
what is the structure of a nucleotide ?
- made up of a pentose monosaccharide (5 carbon atoms)
- phosphate group
- nitrogenous base
what is a nitrogenous base ?
a complex organic molecule containing 1/2 carbon rings + nitrogen
how are nucleotides linked together ?
- condensation reactions
how do the nucleotides link together ?
- phosphate group of a 5th carbon of a pentose sugar covalently bonds with the hydroxyl group of the 3rd carbon of pentose sugar of another nucleotide
what bonds form between nucleotides ?
phosphodiester bonds
what do the polynucleotides form ?
a long strong sugar backbone with a base attached to each sugar
what reaction reverses polynucleotides being linked together ?
hydrolysis reaction
what is the sugar in DNA ?
deoxyribose
how many bases in the nucleotides of DNA ?
4
what 2 groups are the bases split into ?
purines
pyrimidines
what are pyrimidines ?
smaller bases with single ring carbon structures
what are purines ?
larger bases with double ring carbon structures
which bases are pyrimidines ?
thymine
cytosine
which bases are purines ?
adenine
guanine
how is DNA a double helix ?
it is made up of 2 strands of polynucleotides coiled into a helix
how are the 2 strands of DNA held together ?
hydrogen bonds between bases (ladder rungs)
strands of DNA are described as antiparallel, what does this mean ?
the 2 strands run in opposite directions
what does the pairing between bases allow DNA to do ?
be copied and transcribed
how do the bases pair ?
adenine + thymine
guanine + cytosine
each strand of DNA has a phosphate group (5’) at one end. what is the other group at the other end ?
hydroxyl (3’)
what are the base pairing rules for adenine + thymine ?
they form 2 hydrogen bonds
what are the base pairing rules for cytosine + guanine ?
they form 3 hydrogen bonds
what is the base pairing rule known as ?
complementary base pairing
how do purines and pyrimidines pair together ?
- a small purine always joins to a large pyrimidine
why does a small purine always bind to a larger pyrimidine ?
to maintain a constant distance between the DNA backbones - parallel polynucleotide chains
how does the sequence of bases along DNA carry genetic information ?
in the form of a code
what does ribonucleic acid (RNA) do ?
play a role in the transfer of genetic information from DNA to proteins
why can’t DNA leave the nucleus ?
it is long and to large
how do we overcome the issue of DNA not being able to leave the nucleus ?
a short section of the long DNA molecule corresponding to the desired gene is transcribed into mRNA
what is messenger RNA ?
a polymer composed of nucleotide monomers - a shorter replication of the desired gene needed from the DNA
which pentose sugar is used in RNA ?
ribose
which base is replaced with what ?
thymine with uracil
what are the bonds in RNA nucleotides ?
phosphodiester bonds
why are RNA molecules used to transfer genetic information ?
they are small enough to leave the nuclear pores and travel to the ribosomes in the cytoplasm where protein synthesis occurs
what happens to RNA molecules after protein synthesis ?
they are degraded in the cytoplasm
phosphodiester bonds are hydrolysed and RNA nucleotides are released and reused
why do cells divide ?
growth
repair of tissues
what is produced from cell division ?
2 daughter cells which are genetically identical to the parent cells and each other (identical base sequence)
what happens in preparation of DNA replication to the strands of DNA ?
- 2 strands of DNA unwinds and unzips
- separated strands become template strands
what is a template strand ?
a single strand of DNA which acts as a template for the creation of a new double strand DNA molecule
which bonds are broken when the 2 DNA strands separate ?
hydrogen bonds holding complementary bases together
what happens to the complementary strands of DNA ?
free DNA nucleotides pair with the complementary bases which have been exposed and hydrogen bonds form
when complementary base pairing in DNA replication had occurred how do new nucleotides join to other nucleotides ?
phosphodiester bonds
what is semi conservative replication and how does this happen with DNA replication ?
- 2 molecules of DNA are produced each with 1 new and 1 original strand from the original DNA
what does DNA helicase do during DNA replication ?
- helps to unwinds the 2 separate strand of DNA
how does helicase unwind the DNA ?
it travels along the DNA backbone, catalysing reactions that break the hydrogen bonds (unzipping)
what does DNA polymerase do in DNA replication ?
catalyse the formation of phosphodiester bonds between free nucleotides which pair with newly exposed bases
what is continuous replication ?
- DNA polymerase moves along the template strand in the same direction
- it can only bind to the 3’ end so moves in a 3-5 direction
- DNA only unzips in 1 direction so DNA polymerase has to replicate each of the template strands in opposite directions
- strand which is unzipped from the 3’ end is continuously replicated as strands unzip
what is discontinuous replication ?
- the other strand is unzipped from the 5’ end so DNA polymerase and has to wait until a section of that strand has been unzippped then work back along that strand
- DNA is joined in sections which are then joined
how does a mutation occur ?
sequences of bases aren’t matched correctly
random
spontaneous
what could happen if there is a mutation ?
an incorrect sequence may occur in a newly copied strand
how do organisms pass genetic information from one generation to the next ?
via genetic code
what is genetic code ?
the sequence of bases in DNA which are the instructions for the sequences of amino acids in the production of proteins
why is the production of proteins important ?
they are the foundations for the different physical and biochemical characteristics of living things
where are the instructions to build up proteins that DNA carries contained ?
in the sequences of bases along the chain of nucleotides which make up the 2 strands of DNA
what is the code in the base sequences called ?
a triplet code
what is a triplet code ?
a sequence of 3 bases, called a codon
what is a codon ?
a sequence of 3 bases
what is a gene ?
a section of DNA that contains the complete sequence of codons to code for an entire protein
the genetic code is universal - what does this mean ?
all organisms use it
how many codons are possible to make ?
64
( 4 bases - 4x4x4)
what types of codons are there ?
start codon
stop codon
what is the start codon ?
the codon which signals the start of a sequence which codes for proteins
if the codon is in the middle of a gene what does it code for ?
amino acid methionine
what do stop codons do ?
- they don’t code for any amino acids
- they signal the end of a sequence
why are start codons important ?
to ensure the codons are read from base 1 not bases 2/3 so the genetic code does not overlap
how is the genetic code degenerate ?
there are lots more codons than amino acids so amino acids can be coded for by more than 1 codon
where does protein synthesis happen ?
ribosomes
how is protein syntheisis happening in the ribosomes a problem for DNA ?
it is too large to leave the nucleus
how do we solve the problem of DNA being too large to leave the nucleus in protein synthesis ?
bases sequences of genes are copied and transported to the site of protein synthesis via transcriptions
what happens during transcription -
produces shorter molecules of RNA
what is the process of transcription ?
1 - a section of DNA with the desired gene unwinds & unzips beginning the start of a codon
2 - hydrogen bonds are broken
3 - only 1/2 strands of DNA contains desired gene
4- the other strand is complementary & the template strand
5 - free RNA nucleotides pair with complementary bases on antisense strand
6 - phosphodiester bonds are formed between RNA molecules via RNA polymerase
7 - transcription stops at the end of a gene
8 - completed short strand is mRNA
- mRNA detaches from DNA & leaves nucleus
9 - DNA double helix reforms and mRNA goes to ribosome
which enzyme is involved in unzipping the DNA strand ?
helicase
what is the sense strand ?
the section and strand of DNA which contains the correct protein code
what is the antisense strand ?
the strand which has the complementary bases to the sense strand
what is the antisense strand also known as ?
the template strand
what does the template strand allow ?
for the complementary RNA strand to carry the same bases as the sense strand
the free RNA nucleotides pair with the complementary bases on the antisense strand, which bases are different from DNA ?
thymine is swapped with uracil
which enzyme forms the phosphodiester bonds between the RNA molecules ?
RNA polymerase
which type of RNA forms the short strand of DNA ?
messenger RNA
after transcription, what happens ?
translation
how are ribosomes structured ?
there is 1 larger subunit and 1 smaller subunit composed of equal amounts of protein
what does ribosomal RNA do ?
maintain the structural stability of the protein synthesis sequence and plays a biochemical role of catalysing the reaction
how is rRNA formed ?
by the ribosomal subunits
what does the mRNA do after leaving the nucleus ?
it binds to the specific site on a small ribosome subunit
- the ribosome holds the mRNA in position whilst it is decoded into a sequence of amino acids
what is tRNA used for ?
used for the translation of mRNA
what is the structure of tRNA ?
- composed of a strand of RNA folded into 3 bases
what are the 3 bases which fold into RNA called ?
the anticodon
what are the steps of translation ?
- anticodon binds to the complementary codon on mRNA via base pairing rules
- tRNA carries the amino acid corresponding to that codon
- when tRNA anticodons bind to complementary codons amino acids are brought together in the correct sequence forming the primary structure of protein coded for by mRNA
- amino acids are added one at a time
- ribosomes act as a binding site for mRNA and tRNA catalyse the assembly of proteins
summaries translation ?
- mRNA binds to small subunits on ribosomes at its start codon
- tRNA with complementary anticodon binds to start codon - this tRNA carries methionine
- another tRNA with anticodon carries the corresponding amino acid to corresponding codon on mRNA
- first amino acid transfers to amino acid forming a peptide bond
- ribosomes move along mRNA releasing tRNA forming proteins
what is the start codon ?
AUG
what enzyme catalyses the peptide bonds which form between tRNA called in translation ?
peptidyl transferase
what happens at the end of translation ?
- amino acids are added to the chain of amino acids each time until the ribosome reaches the end of mRNA at the stop codon
- polypeptide is released
in translation, what stage of the protein is formed ?
amino acids join together to form the primary structure which fold into the secondary and tertiary structure
what do the folding and the bonds of the protein determined by ?
the sequence of amino acids in the primary structure
how are proteins made so they can be simultaneously identical ?
many ribosomes follow on mRNA behind the first
what do cells need energy for ?
- synthesis
- transport
- movement
how do cells need synthesis ?
e.g, large molecules such as proteins
why do cells need transport , e.g
pumping molecules or ions across cell membranes by active transport
give an example of when movement is used in cells ?
protein fibres in muscles fibres which cause contraction
what does ATP stand for ?
adenosine triphosphate
how is ATP structured ?
3 phosphate groups
pentose sugar - ribose
nitrogenous base
what is the base always in atp ?
adenine
what is ATP used for ?
energy transfer in all cells and living things
what is ATP known as ?
universal energy currency
how is energy released ?
when bonds are formed
energy is needed to break bonds however only a small amount why is this useful ?
not a lot of energy is needed to break the bond holding the last phosphate group, but lots of energy is released
what do the released phosphate groups do (ATP)?
undergo bond formation - 30.6 KJ energy released
what type of reaction released energy ?
hydrolysis
hydrolysis of ATP is coupled with energy requiring reactions - what does this mean ?
it happens simultaneously with energy requiring reactions
what is ATP hydrolysed into ?
adenine diphosphate + a phosphate ion
why isn’t ATP a good long term memory store ?
instability of phosphate bonds in atp
what are better stores of energy ?
fats and carbohydrates
why are fats and carbohydrates better stores of energy ?
energy released in the breakdown of these molecules create ATP via phosphorylation
what is phosphorylation ?
a phosphate molecule is reattached to an ADP molecule
what kind of reaction is phosphorylation ?
condensation reaction
why don’t cells store large amounts of ATP ?
it is instable
why is ATP rapidly formed ?
phosphorylation
what kind of store is ATP ?
a good immediate energy store
what are the properties of ATP ?s
small
water soluble
contains bonds between phosphates with intermediate energy
releases energy in small quantities
easily regenerated
why is ATP being small good ?
moves easily in and out of cells
why is ATP being water soluble good ?
energy requiring processes often happen in aqueous environments
why is it being a good intermediate energy source good ?
large enough to be useful for cellular reactions
not too large so energy is wasted as heat
why is atp releasing energy in small quantities good ?
quantities are suitable to most cellular needs
energy isn’t wasted as heat
why is atp being easily regenerated good ?
it can be recharged with energy
