Nucleotides and nucleic acids

Chapter 3.8 to 3.11

structure of nucleotide monomer

phosphate group - pentose sugar - nitrogenous base

types of nucleic acids

DNA and RNA and ATP

how many hydrogen bonds A an T have

2

how many hydrogen bonds do C and G have

3

purines

A and G, larger bases with double carbon ring structure

pyrimidines

C and T and U, smaller bases with single carbon ring structure

nitrogenous bases names

Adenine, cytosine, thymine, guanine, uracil

bond between phosphate group and pentose sugar

ester bond

bond betweeen pentose sugar and nitrogenous base

glycosidic bond

number of pairs of chromosomes humans have

23

DNA features

DNA has 2 strands, DNA has a deoxyribose pentose sugar, Bases are ACTG, DNA’s subunit is a DNA nucleotide, DNA’s bond between nucleotides is phosphodiester and hydrogen bonds

RNA features

RNA has 1 strand, RNA has a ribose pentose sugar, Bases are ACGU, RNA’s subunit is RNA nucleotide, RNA’s bond between nucleotides is phosphodiester bonds only

how polynucleotides synthesise

nucleotides joined by a condensation reaction forming phosphodiester bonds between the hydroxyl group on carbon 3 on one nucleotide (pentose sugar) and the phosphate group on carbon 5 of the next nucleotide

how polynucleotides breakdown

hydrolysis reaction breaks down phosphodiester bonds

phosphodiester bond

made of a phosphate group and two ester bonds

ATP

Adenosine Triphosphate

ADP

adenosine diphosphate

types of activity cells require energy for

synthesis, transport, movement

ATP strucutre

3 phosphate groups, ribose sugar, adenine base

ADP structure

2 phosphate groups, ribose sugar, adenine base

AMP structure

1 phosphate groups, ribose sugar, adenine base

process of phosphorylation

ATP is created by reattaching a phosphate group to an ADP molecule, this is a condensation reaction (water is removed)

word equation for hydrolysis of ATP

ATP + water > ADP + Pi (inorganic phosphate) + energy

why ATP is not a good long term energy store

the phosphate bonds in ATP are unstable because the bonds holding the phosphates together in ATP are relatively weak

properties of ATP that make it useful as the universal energy currency

Small - can easily move in and out of cells. Water soluble - ATP is rapidly hydrolysed at extreme water pH but stable at 7pH. Energy released in small amounts - so its not wasted as heat. Immediate energy store - bonds bw phosphate groups break releasing energy. Can be easily recharged with energy

how ATP/phosphorylation releases energy

little energy is needed to break the (weak) bond holding together the phosphate groups in ATP but when when an inorganic phosphate bonds with ADP a lot of energy is released (about 30.6kJmol-1)

DNA structure

the DNA backbone (made up of alternating phosphates and sugars) give DNA an asymmetrical structure therefore a direction for each strand (all strands go in the direction 5’ to 3’ with each strand running antiparallel to the other)

how DNA is a double helix

hydrogen bonds hold complementary base pairs together on adjacent strands to form a double helix (1 complete turn every 10 base pairs). twists so DNA can packed as close together as possible to be more efficient

difference between 5’ and 3’ end of DNA strands

5’ has a phosphate group off carbon 5 and strand ends with that phosphate group, 3’ has a hydroxyl group off carbon 3 and strands ends with that deoxyribose sugar

why do cells replicate

growth of individual cell/whole organism, repair tissues/cell replacement, asexual reproduction

role of helicase in semi-conservative DNA replication

breaks hydrogen bonds between nitrogenous bases to separate the 2 strands of DNA double helix

role of DNA polymerase in semi-conservative DNA replication

joins entire nucleotides together (sugar-phosphate backbone) via phosphodiester bonds, works in 3’ to 5’ direction

importance of conserving genetic information with accuracy

Retaining one original DNA strand maximises accuracy during DNA replication, as each new DNA strand is created from an existing template. New cells will always contain the same genetic info as its parent. Important because cells in our body are replaced regularly and we need the new cells to carry out the same roles as the parent cells.

Random, spontaneous mutations

Although the process of DNA replication is highly accurate, copying errors do occur. Like: bases inserted in the wrong order, an extra base inserted, a base being left out Occur at random and spontaneously.

process of semi-conservative DNA replication

DNA helicase breaks hydrogen bonds, strands separate, free nucleotides attach to their complementary base, DNA polymerase joins nucleotides with phosphodiester bonds, 2 identical polynucleotide DNA chains

which strands are continuous/discontinuous

leading strand = continuous, lagging strand = discontinuous (okazaki fragments)

features of the genetic code

universal (all organisms use DNA), degenerate code (4 bases and 64 different codons but only 20 amino acids so there are more than 1 codon that code for the same amino acid), Non-overlapping (has stop and start codons), triplet (3 bases > 1 codon > 1 amino acid)

name of start codon if in the middle of a codon and not signalling the start of a sequence

methionine

how a gene determines the sequence of amino acids in a polypeptide

gene contains all codons required to code for a specific protein

role of RNA polymerase

forms the RNA backbone therefore forming mRNA by joining free RNA nucleotides together with phosphodiester bonds

transcription

(happens 1st, formation of mRNA) 1) DNA helicase breaks hydrogen bonds bw base pairs, DNA uncoils, separate into 2 strands. 2) DNA template/antisense strand used by RNA polymerase to make mRNA. 3) Free RNA nucleotides complementary base pair to antisense strand, joined by phosphodiester bonds made by RNA polymerase, forms 1 strand of mRNA. 4) mRNA leaves nucleus thru nuclear pore

translation

(happens 2nd, formation of polypeptides) 1) mRNA binds to small ribosome subunit. 2) tRNA arrives at ribosome with an amino acid and exposed anticodon. 3) tRNA anticodon and mRNA codon complementary base pair 4) adjacent amino acids are joined by peptide bonds in a reaction catalysed by peptidyl transferase, tRNA detach from amino acids. 5) polypeptide is formed (until stop codon reached on mRNA)

role of mRNA

carry info that codes for a protein from the nucleus to the ribosome where tRNA can bind to mRNA’s codons

role of tRNA

bring amino acids to ribosome for protein production, has anticodon to complementary base pair to mRNA codon so amino acids are in the right sequence

role of rRNA

catalyses peptide bond formation, maintain structural stability of protein synthesis

explain why DNA replication is considered to be semi-conservative

original strand acts as the template for the new strand, 1 strand is from the original DNA and 1 strand is formed

explain why complementary base pairing is important in DNA replication

reduces the occurrence of mutations, allows reformation of hydrogen bonds, DNA can be replicated without error

explain the uses of all the different base combinations

some are used as stop or start codons, several codons code for the same amino acid

dna pag!!!!