2.1.3 nucleotides and nucleic acids

what does nucleotides consist of?

• five carbon sugar molecules in the centre (pentose sugar)

• nitrogen containing molecule called a base and sometimes referred to as a nitrogenous base

• negatively charged phosphate group

what is the difference between RNA and DNA specifically with the sugar present?

They both have pentose sugar but DNA’s pentose sugar is called deoxyribose so has one fewer oxygen atom compared to RNA which is called ribose

What are the DNA bases called?

• thymine

• cytosine

• adenine

• guanine

which one of the DNA bases are purines? And why?

• adenine

• guanine

contains 2 carbon nitrogen rings

Acronym- AnGels are PURe with 2wINGS

Which ones of the DNA/RNA bases are pYrimidines? And why?

• thYmine

• cYtosine

• uracil

contains 1 carbon nitrogen ring

How can a polynucleotide form?

Form bond between carbon 5 phosphate group of one nucleotide and hydroxyl group on carbon 3 of pentose sugar of the other molecules

what is the bond between 2 nucleotides called? And what type of reaction is it?

phosphodiester bond

condensation reaction

Describe how nucleotides are joined together in DNA (3 marks)

Phosphodiester bond

Between the phosphate group of one nucleotide and the deoxyribose sugar of the next

Catalysed by DNA polymerase

Describe how two single polynucleotide strands are joined to make a double

helix (3 marks)

Hydrogen bonding between base pairs

2 bonds between A and T, 3 bonds between C and G

Complementary base pairing A-T and C-G

Two antiparallel polynucleotide strands twist to form double helix

Name the type of RNA found within the nucleus of a cell (1)

mRNA / messenger RNA

Name the type of reaction that breaks the bonds between RNA nucleotides

(1)

hydrolysis

what are the bases for DNA?

• adenine

• thymine 

• guanine

• cytosine

what are the bases for RNA?

• adenine

• uracil

• cytosine

• guanine

what is molecule that is formed when two nucleotides join together?

dinucleotide

what is a molecules with multiple bonded nucleotides called?

polynucleotide

how many bonds between adenine and thymine?

2

how many bonds between cytosine and guanine?

3

what is the structure of DNA?

• 2 polynucleotide strands

• with sugar phosphate backbone on outside

• bases in centre

• strands held together by hydrogen bonds formed between bases on opposite strands

is the distance between sugar phosphate backbone constant down the DNA molecule? And why?

Yes, because purine on one strand pairs with a pyrimidine on the opposite strand

The 2 polynucleotides in DNA can be described as _______.

antiparallel

they run in opposite directions

What are three difference between DNA and RNA?

• DNA is found in nucleus and RNA in cytoplasm

• DNA is extremely long and RNA is relatively shorter

• DNA is 2 polynucleotide strands in double helix and RNA is 1 polynucleotide strand

Explain the steps of semi-conservative DNA replication

• enzyme DNA helicases attaches to the DNA molecule and causes hydrogen bonds between the bases to break causing polynucleotide strands to separate

• free nucleotides line up with complementary bases on DNA strand and is held together by hydrogen bonds

free nucleotide= activated nucleotide 

• second enzyme attaches, DNA polymerase moves down molecule and catalyses the formation of phosphodiester bond between nucleotides (condensation reaction)

•  activated nucleotides lose their 2 extra phosphate group and provide energy for reaction

• now 2 copies of our double stranded DNA. With each DNA molecule has 1 original strand of DNA and 1 new

DNA is copied accurately but sometimes incorrect bases are inserted into growing nucleotide strand so DNA nucleotide has changed. This is called ______. And happens ______.

mutations

spontaneously

what is evidence for semi-conservative replication?

In1958 Matthew Meselsohn and Franklin Sahl  demonstrated that DNA replication was semi-conservative using E.Coli 

What is explanation of results in Semi-conservative replication?

• parental generation, both strands made with 14N

• first generation DNA made of one strand 15N and one strand 14N

• second generation some DNA made of 2 strands of 14N and some made of 15N and 14N

what are the parts of ATP?

• adenine

• ribose sugar

• 3 phospate groups

what is one adenine and a ribose called?

adenosine

what is one adenine, a ribose, a phosphate called?

adenosine monophosphate (AMP)

what is one adenine, a ribose, 2 phosphate called?

adenosine diphosphate (ADP)

what is one adenine, a ribose, 3 phosphate called

adenosine triphosphate (ATP)

what is adding a phosphate group called?

phosphorylation

what is the bonds between phosphate groups called?

phosphoanhydride bond

what is another name for triplet?

codon

what is meaning of degenerate?

more than one codon that codes for each amino acid

what is meaning of non-overlapping?

each base sequence is only read once

what is meaning of universal?

same codon codes for same amino acid in all organisms

what are three rules about genetic code?

• degenerate

• non-overlapping

• universal

what are bonds between bases?

hydrogen bonds

Is dna antiparallel or parallel?

antiparallel

what is bond between deoxyribose and phosphate?

phosphodiester bond

what are features of mRNA?

• made in nucleus

• small enough to pass through nuclear pores

• carries genetic code for protein to ribosomes in cytoplasm

• uses Uracil instead of Thymine

what are features of tRNA?

• amino acid is determined by anticodon

• one strand folded back on itself

• anticodon this is complementary to codon on mRNA

explain process of transcription

• DNA helicase separates 2 strands of DNA by breaking  hydrogen bonds

• RNA polymerase moves along on strand of DNA (template stand) causing RNA nucleotides to align with complimentary bases and join together with phosphodiester bond

• RNA polymerase moves along, DNA strands rejoin behind it

explain the process of translation

• one end of the mRNA attaches to the ribosome

• a tRNA molecule that has complementary anticodon also attaches to the ribosome and brings amino acid

• a second tRNA molecule then binds to the next codon on the mRNA and brings amino acid

• the ribosome moves along the mRNA and joins the 2 amino acids together by a peptide bond (rRNA catalyses this, specifically peptidyl transferase)

• First tRNA molecule is released as max 2 tRNA molecule at same time

• this continues until a stop codon is reached