nucleic acids Flashcards
general structure of a nucleotide
- pentose sugar (ribose, deoxyribose)
- phosphate
- organic nitrogenous base
what is a polynucleotide?
and examples
many nucleotide monomers bonded into a chain
in a condensation reaction
e.g. DNA, RNA
what are the 5 nitrogenous bases
adenine
guanine
thymine
cytosine
uracil
what are the purines
adenine
guanine
- two rings
what are the pyrimidines
thymine
cytosine
uracil
- one ring
ATP structure
- nitrogenous base adenine
- ribose sugar
- 3 phosphate groups
how is ATP formed?
in an endergonic reaction
ADP + Pi (inorganic phosphate) combine = ATP + water
energy to combine ADP + Pi comes from exergonic reactions (cell respiration)
how much energy is released when ATP is hydrolysed?and how?
30.6 kJ mol-1
- ATPase hydrolyses bond between 2nd+3rd phosphate
- reversible reaction
- made continuously as ATP can’t be stored in large quantities
why is ATP the universal energy currency in organisms?
- it is a common energy source in reactions
- found in all cells of all organisms
- high energy bonds
- energy released when bonds are hydrolysed
why is ATP better than glucose?
- ATP hydrolysis = single reaction = immediate energy release
- ATP requires 1 enzyme
- ATP releases energy in small amounts, when and where its needed
- ATP is the common energy source for many chemical reactions
what are the roles of ATP?
metabolic processes
active transport
movement
nerve transmission
secretion
role of ATP in metabolic processes
builds large, complex molecules
role of ATP in active transport
changes shape of carrier proteins
allows movement against conc gradient
role of ATP in movement
used for muscle contraction
role of ATP in nerve transmission
used in sodium-potassium pumps
transport across axon membrane
role of ATP in secretion
package into vesicles
DNA structure
- 2 polynucleotide strands, wound in double helix
- strands are antiparallel
- 4 bases
- pentose sugar deoxyribose
- sugar + phosphate form backbone, protecting genetic info
- stable, large = genetic info passed down generations
how are DNA polynucleotide strands antiparallel?
they run in opposite directions but lie parallel to each other
- one runs 5 prime to 3 prime end
- other runs 3 prime to 5 prime end
what is complementary base pairing
baes pair up, hydrogen bonds form between
- A + T = 2 hydrogen bonds
- G + C = 3 hydrogen bonds
RNA structure
- single stranded polynucleotide
- pentose sugar ribose
- 4 bases (uracil not thymine)
mRNA, tRNA, rRNA
function of messenger RNA
- complementary copy of DNA genetic code in nucleus during transcription
length relates to length of gene transcribed
attaches to ribosome in cytoplasm
ribosomal RNA function
form ribosomes
transfer RNA structure and function
- clover leaf shape
- carries an amino acid at 3 prime end and an anticodon arm to attach to the mRNA
DNA vs RNA
deoxyribose - ribose
double stranded - single stranded
A,T,G,C - A,U,G,C
long - short
what are the 2 functions of DNA?
replication: copying an original DNA molecule
protein synthesis: sequence of bases determine amino acid sequence in proteins
stages of DNA replication
- DNA helicase breaks hydrogen bonds between bases in double helix
- unwinds DNA, exposing unpaired bases
- free nucleotides in nucleoplasm bind to complementary bases on unzipped strand (template strand)
- DNA polymerase joins adjacent nucleotides together, forming phosphodiester bonds between sugar and phosphate in condensation reaction
- 2 new DNA molecules formed (1 old, 1 new)
types of DNA replication
conservative
semi-conservative
dispersive
what is conservative DNA replication
parental strand remains
new helix made
what is semi-conservative DNA replication
parental helix separates
2 strands act as templates
what is dispersive DNA replication
2 new helicases
fragments from both parental strands
stages of the Meselson-Stahl experiment
- grow bacteria with heavy isotope (nitrogen 15) = heavy strand
- remove heavy bacteria, add into light nitrogen isotope (N14). allow bacteria to divide. DNA contains 1 new (N14), 1 old (N15) strand = intermediate density
- grow 1 more generation. 50% hybrid = intermediate density. 50% N14 = light density
(spun in centrifuge)
what is the genetic code?
a linear, triplet, non-overlapping, degenerate, unambiguous, universal code for the production of polypeptides
how is the genetic code degenerate / redundant?
more than 1 triplet can encode each amino acid
how is the genetic code punctuated?
3 triplet codes don’t code for amino acids
they code for stop codons
how is the genetic code universal?
same triplets code for the same amino acids in all organisms
how is the genetic code non-overlapping?
each base only occurs in 1 triplet
feature of eukaryotic genes
discontinuous
contain coding exons and non-coding introns
RNA code too long = introns cut out of pre-mRNA by endonucleases = mRNA. leaves exons joined by ligases.
features of prokaryotic genes
continuous
lack non-coding sequences
mRNA directs synthesis
what are exons?
regions of DNA that contain the code for proteins
present in final mRNA
what are introns?
regions of non-coding DNA
removed from pre-mRNA
what is the triplet code?
amino acids are coded for by triplets of bases in DNA. DNA is transcribed to produce codons in mRNA, then translated to produce sequences of amino acids.
- 20 amino acids
- 4 times 4 times 4 = 64 = more than 20 = degenerate = different triplets code for the same amino acid
further modifications of polypeptides
- addition of carbohydrates (glycoprotein), lipids (lipoprotein), phosphate (phosphoprotein)
- polypeptides combined (haemoglobin - folded, 4 polypeptide chains, 4 haem groups)
stages of protein synthesis
transcription
movement of mRNA to ribosomes
amino acid activation
translation
stages of transcription
- DNA helicase unzips section of DNA (gene), breaks hydrogen bonds between complementary base pairs. exposes unpaired bases on template strand
- RNA polymerase links to template (coding) DNA strand. attaches mRNA nucleotides to complementary base pairs (A+U, G+C)
- DNA strand rewinds into helix behind RNA polymerase
- continues until stop codon. RNA polymerase leaves DNA
- newly made pre-mRNA leaves DNA.
- post-transcriptional modification of pre-mRNA. removes introns, leaves exons = functional mRNA
- mRNA leaves nucleus
stages of mRNA moving to ribosomes
mRNA leaves nucleus via nuclear pores into cytoplasm
attaches to ribosome
stages of amino acid activation
enzymes attach amino acids to specific tRNA molecule
needs ATP
anticodon forms
stages of translation
- mRNA leaves nucleus, attaches to small sub unit of ribosome
- large subunit of ribosome has 2 attachment sites for tRNA. ribosome holds mRNA and tRNA with attached amino acid. peptide bond forms between amino acids = polypeptide chain
- ribosome binds to start codon on mRNA. tRNA binds to ribosome
- ribosome moves along mRNA
- continues until stop codon
codon on mRNA determines tRNA with complementary base code carrying specific amino acid
what is the 1 gene 1 polypeptide hypothesis?
each gene is responsible for the synthesis of a single polypeptide
why not the 1 enzyme 1 polypeptide hypothesis?
not all proteins are enzymes
why not the 1 protein 1 polypeptide hypothesis?
some proteins are made of more than 1 polypeptide
e.g. haemoglobin
