nucleotides and nucleic acids Flashcards
2.1.3 (23 cards)
describe what nucleotides are
-monomers from which nucleic acids are made
-always contain a pentose sugar, nitrogenous base and a phosphate group
-joined together in condensation reactions via phosphodiester bonds to form polynucleotides
what does a DNA nucleotide contain
-deoxyribose (pentose) sugar
-adenine, thymine, cytosine or guanine nitrogenous base
-a phosphate group
what does an RNA nucleotide contain
-ribose (pentose) sugar
-adenine, uracil, cytosine or guanine nitrogenous base
-phosphate group
-make mRNA, tRNA and rRNA
features of DNA that allows passing of genetic information
-sugar phosphate backbone protecting the coding bases inside the helix
-double stranded so acts as a template in DNA replication
-large molecule so stores a lot of info
-double helix making it compact
-complementary base pairing allows accurate DNA replication
-weak hydrogen bonds allows strands to separate in DNA replication
what are purines and pyridines
purines- larger bases containing 2 carbon rings (A,G)
pyrimidines- smaller bases containing 1 carbon ring (T,C)
describe the complementary base pairings
-adenine and thymine pair w/ 2 hydrogen bonds
-cytosine and guanine pair w/ 3 hydrogen bonds
-a smaller pyramidine base always bonds to a larger purine base
compare similarities and differences between DNA and RNA
similarities;
-both contain phosphate group, nitrogenous base and pentose sugars
differences;
-DNA is double stranded, RNA is single stranded
-DNA is long, RNA is short
-DNA has thymine, RNA has uracil
-DNA has a deoxyribose sugar, RNA has a ribose sugar
what is ATP and it’s uses
-adenosine triphosphate
-contains adenosine (ribose sugar and adenine) and 3 phosphate groups (triphosphate)
-broken down in hydrolysis reactions and re-synthesised in condensation reactions
roles;
-involved in energy transfer within cells
-aids in movement eg muscle contraction
-active transport of molecules against concentration gradient
-synthesis of large molecules
-secretion of substances from cells
how does the properties of ATP relate to it’s function
-hydrolysis of ATP releases a small amount of energy so little energy is lost as heat
-ATP is broken down in one step so energy is released quickly
-ATP is rapidly re-synthesised so it’s always readily available
-bonds between phosphate groups are unstable, have low activation energy and so are easily broken
-soluble so can easily be transported around cells
-the inorganic phosphate released in ATP hydrolysis can be used to phosphorylate other compounds, often making compounds more reactive
what is DNA replication, where and when does it happen?
-occurs during interphase in the nucleus
-involves the copying of a double stranded helix to form two identical helices
explain the enzymes involved in DNA replication
1- DNA helicase unzips whole double helix by breaking hydrogen bonding between anti-parallel strands
2- DNA polymerase joins free nucleotides together to form complimentary strands. moves from 3’ to 5’
why is semi-conservative replication
when each copy of a DNA strand is made up of one original strand and one new strand.
-the original strand serves as a template
-both DNA molecules formed are identical
explain the steps in DNA replication
1-DNA helicase unzips the DNA by breaking hydrogen bonds.
2-free nucleotides attach to their complementary bases and the hydrogen bonds reform between them.
3-once new nucleotides have lined up, DNA polymerase attaches them and new phosphodiester bonds form between them.
4-all nucleotides along the whole length are joined forming two complete identical chains, each retaining half the original DNA
explain mutations during DNA replication
-random spontaneous mutations can occur in the sequence of bases, and could change them.
what is a codon
sequence of 3 bases the code for an amino acid
what is a gene
complete sequence of bases that codes for an entire protein
what is AUG
starting gene that codes for a protein
codes for methionine
what are stop codons
do not code for any amino acid and signal the end of a gene
how would you describe the genetic code
-degenerate
-universal
-non overlapping
purpose of start codons?
ensures that triplet bases are read from base 1, not 2 or 3 so the genetic code is non overlapping
what are the 2 steps of protein synthesis and where do they occur
1- transcription in the nucleus
2- translation in the ribosomes
explain the steps of transcription in protein synthesis
-RNA polymerase binds to gene and unzips by breaking hydrogen bonds
-antisense strand acts as template
-free RNA molecules nucleotides align with template strand through complementary base pairing
-RNA polymerase catalyses the formation of phosphodiester bonds between nucleotides
-complementary mRNA strand formed
-process ends when RNA polymerase reaches stop codon, detaches from DNA and terminates transcription
-mRNA detaches from DNA and DNA rewinds into its double helix structure
explain the steps of translation in protein synthesis
-ribosome attaches to mRNA at AUG ( start codon)
-tRNA molecule carrying specific amino acid with anticodon complementary to start codon binds to mRNA
-second tRNA molecule carrying specific amino acid with anticodon complementary to the next codon binds to mRNA
-amino acids carried by first 2 tRNA molecules are linked with a peptide bond using ATP
-first tRNA molecule detaches from mRNA and is free to fetch another amino acid
-ribosome moves along mRNA, allowing another tRNA molecule carrying next amino acid to bind to the next codon
-process repeats, elongating amino acid chain
-sequence continues until tRNA reaches stop codon
-completed polypeptide chain detaches from ribosome
