topic two - nucleic acids - mr hedditch Flashcards
state the two types of nucleic acids?
DNA – deoxyribonucleic acidcontains the pentose sugardeoxyribose
RNA – ribonucleic acidcontains the pentose sugar
ribose
what does each DNA nucleotide contain?
a phosphate group
a deoxyribose sugar molecule (pentose – 5C)
one of four nitrogenous bases
what are the four nitrogenous bases in DNA?
adenine (A)
thymine (T)
cytosine (C)
guanine (G)
what are nucleotides monomers of?
nucleic acids
how are the tree subunits (phosphate, deoxyribose, nitrogenous base) joined together?
joined by covalent bonds formed by condensation reactions
what different about the RNA to DNA?
RNA has a ribose sugar and instead of thymine its uracil
state the similarity between DNA and RNA?
they are both joined by covalent bonds and formed by a condensation reaction
are DNA purines or pyrimidines and why?
they are purine bases because they have two carbon-nitrogen rings, joined together
these are
adenine
guanine
are RNA purines or pyrimidines and why?
they are pyrimidine bases because they have a single carbon-nitrogen ring (smaller than a purine base)
these are
cytosine
thymine (DNA only) /Uracil (RNA only)
draw the simple diagram of a RNA nucleotide with any one of the bases?
check in book or olc
draw the simple diagram of a DNA nucleotide with any one of the bases?
check in book or olc
define a phosphorylated nucleotide?
a nucleotide with one or more phosphate groups added to it
state the two types of phosphorylated nucleotides and how many phosphate groups they contain?
ADP – adenosine diphosphate (two phosphate groups)
ATP – adenosine triphosphate (three phosphate groups)
what makes up the base and the sugar of ADP & ATP?
both molecules have the nitrogenous base adenine
and the pentose sugar ribose
draw the simple diagram for ADP and ATP?
check in book or on the olc
define ATP?
universal energy source meaning it does the same job and production in all living specimens
how is ATP produced?
through a series of oxidation reactions that break down food
why is ATP continuously hydrolysed?
so ADP can be released and than re-synthesised
can ATP be transported from cell to cell and why?
no, it must be used in the cell in which it’s made
what is ATP made of?
three phosphate groups and 2 high energy bonds
draw the simple diagram of ATP and ADP?
ATP is three phosphate groups
ADP is two phosphate groups
how is an inorganic molecule produced?
the hydrolysis of ATP to ADP is catalysed by the enzyme ATPase
this release energy as well as an inorganic molecule
what does jointing nucleotides form?
polynucleotides
what happens in respiration (ATP)?
ADP is converted back to ATP by adding a phosphate group
how is a phosphate bond formed?
a condensation reaction takes place between the phosphate group of one nucleotide and the sugar molecule of a second nucleotide
what is base pairing and why does this happen?
A & T
And
C & G
will always pair up
because A&T have have 3 hydrogen bonds and C&G have two hydrogen bonds
what does the high number of hydrogen bonds do to DNA?
it makes it a very stable structure
describe the structure of a double strand?
“antiparallel” This refers to the fact that the sugar phosphate backbones run parallel to each other but in opposite directions
what gives the sugar phosphate backbone?
phosphodiester bonds
draw the simple production of phosphorylation?
check with the olc
what is the amount of energy released when ATP is hydrolysed to ADP?
releases a large amount of energy (30.6kJ mol-1)
what phase does DNA replication occur in?
interphase
why is it important for DNA to be copied accurately?
so that the new cells will contain the correct genes to function properly and to produce the correct protein
why must chromosomes be copied before mitosis?
so that the new cells contain genetic information
state the five stages of DNA replication?
gyrase causes the double helix to unwind
hydrogen bonds between bases are broken by helicase to separate the two strands, which
can act as templates
free nucleotides align next to the exposed bases according to the complementary base-pairing rule
hydrogen bonds form between the free nucleotides and nucleotides of the original strands
DNA polymerase forms phosphodiester bonds between the phosphate of one nucleotide
and the deoxyribose sugar of the next nucleotide, sealing the sugar-phosphate backbone
Why is DNA replication described as “semi-conservative”?
this is because the two original “parent” strands act as templates for the formation of new strands.
each replicated molecule contains one old strand and one new strand
describe what the enzyme ‘gyrase’ does in DNA replication?
unwinds the double helix
describe what the enzyme ‘helicase’ does in DNA replication?
breaks the hydrogen bonds between the two parental strands of DNA, at a number of different points called replication forks
describe what the enzyme ‘polymerase’ does in DNA replication?
joins the nucleotides in the new strand together (makes phosphodiester bonds) to form a sugar-phosphate backbone
is DNA replication accurate and why?
DNA replication is very accurate – this is essential for
genes to be conserved, and is ensured through the action of proof-reading enzymes
name the three types of evidence for semi-conservative replication and what they are?
semi-conservative – the DNA molecule splits and each strand is replicated. Each of the two new molecules contains one strand of original material and one strand
of new material
conservative - parental DNA remains intact and a separate daughter copy is built out of new molecules. Of the two molecules present, one is the original and one is entirely new material
dispersive – the parental DNA is broken down and the nucleotides replicated before being randomly dispersed throughout the new molecules. The new molecules contain both new and original material but not necessarily in equal amounts
what does exonuclease do in DNA replication?
it removes all the RNA which is then filled with DNA
define gene?
a gene is a length of DNA that codes for a polypeptide
why does each gene contain a sequence of DNA triplets?
it determines the amino acid sequence (or primary structure) of a protein
why must a copy of each gene be transcribed into a length of mRNA?
the instructions contained in the genes cannot pass out of the nucleus
define a codons?
a codon is a set of three adjacent nucleotides (bases) on a strand of
mRNA
each codon specifies for one particular amino acid
what does the order of the codons along the mRNA strand determines?
determines the
sequence of the amino acids in the polypeptide
why is the genetic code described as universal?
because the same DNA bases (or mRNA codons)
code for the same amino acids in almost all organisms
why are there three nucleotides in a codon?
There are four bases in DNA:
– adenine, guanine, thymine and cytosine
clearly, it is not possible to have one base
coding for each of the 20 different amino acids
similarly, using two bases would be insufficient
– would only code for 16 different amino acids
using three bases gives 64 possible unique
combinations - more than enough!
the triplet code has spare coding capacity – i.e. there
are more unique codons (64) than there are amino acids to
be coded for (20)
therefore it is possible for several codes to be used to
specify the same amino acid
– e.g. phenylalanine can be coded for by AAA and AAG
– e.g. leucine can be coded for by AAT, AAC, GAA, GAG,
GAT and GAC
because of this, the code is described as degenerate
define degenerate?
degenerate refers to a code in which several
code words have the same meaning. The genetic code is degenerate because there are many instances in which different codons specify the same amino acid
what are the three forms of RNA?
mRNA
messenger RNA
a “copy” of the DNA base sequence of a gene complementary to one strand of the DNA (template
strand). The coding sequence of the mRNA determines
the amino acid sequence in the polypeptide that is
produced
single-stranded, with uracil in place of thymine
rRNA
ribosomal RNA
ribosomes are made of rRNA and protein (two sub-units)
tRNA
transfer RNA
small molecule ~ 80 nucleotides
hydrogen bonds make a stable
clover-leaf shaped structure
20 types – one for each of the different amino acids
delivers (transfers) amino acids to growing polypeptide chains in the ribosome in the specific order directed by mRNA
state the processes of transcription?
the DNA double helix “unzips” as hydrogen bonds
between complementary bases break (due to helicase) and the two polynucleotide strands separate
one DNA strand acts as a template. Free RNA nucleotides
complementary base-pair to the exposed bases on this strand by
forming hydrogen bonds. mRNA contains U in place of T
RNA polymerase forms phosphodiester bonds between the
sugar and phosphate parts of the RNA nucleotides
the mRNA detaches from the template strand of the DNA
the two DNA strands join together by complementary base
pairing (hydrogen bonds reform) and the DNA molecule winds
back up into a helix
ways transcription is similar to DNA replication?
the DNA molecule unwinds and unzips
helicase is involved in breaking hydrogen bonds
exposed bases act as a template for the formation
of a new polynucleotide strand
complementary base pairing ensures that the
message is transcribed accurately
the free nucleotides joining the new polypeptide
chain are joined together by phosphodiester bonds
ways transcription is different from DNA replication?
only one DNA strand, the template strand, is copied
(in DNA replication both strands act as templates)
RNA polymerase joins the sugar-phosphate
backbone (not DNA polymerase)
mRNA is single-stranded and a relatively short
molecule with uracil in place of thymine
Only a single gene is transcribed, whereas in DNA
replication the whole chromosome is copied
what happens in the move from transcription to translation?
mRNA moves out through a nuclear pore and attaches to a
ribosome
what does tRNA transport?
transports amino acids to the ribosome for incorporation into a polypeptide chain
what do hydrogen bonds between the complementary bases do in tRNA?
stabilise the clover-leaf shape
what two things does tRNA have?
an anticodon that is complementary to a codon on the mRNA
three unpaired bases to which a specific amino acid can be attached (called the attachment site)
state what takes place in translation?
during translation, mRNA enters the groove between the small and large ribosomal subunits
the ribosome is large enough for two codons to fit side by side
the very first codon is always the start codon AUG
(codes for methionine)
the anticodon of a tRNA molecule carrying methionine
hydrogen bonds to the first codon to start translation
a second tRNA molecule, carrying the second amino acid coded for, hydrogen bonds to the second codon
a peptide bond is formed between the two amino acids through a condensation reaction
the ribosome moves three bases (one codon) along the mRNA so that another codon is exposed
a third tRNA brings another amino acid which is added
to the dipeptide and so the process continues until a
termination or stop codon (UAA, UAG or UGA) is
reached
there is no tRNA for stop codons, so the polypeptide
chain and mRNA are released from the ribosome
translation takes place in the cytoplasm at the
ribosomes
what are the two subunits in translation?
a large subunit and a small
subunit, bound together with the aid of magnesium ions
– with a groove between them in which the mRNA fits
study the transcription/translation grid sheet?
in biology folder
