A1.2 nucleic acids

What is the biological macromolecule that includes DNA?

• nucleic acid

What are the building blocks of nucleic acids

• nucleotides (repeating monomers)

  • they join together to make nucleic acids through polymerisation (condensation reaction)

What are the 2 types of nucleic acids

• RNA (Deoxyribonucleic acid)

• RNA (ribonucleic acid)

List the 3 components of a nucleotide and draw it

1. pentose sugar

2. nitrogenous base

3. a phosphate group

How do nucleotide units link together? What is this process called?

• sugar-phosphate binding

  • nucleotide units use covalent bonds to form a single strand of DNA/RNA

  • forms between phosphate group (5’C of one pentose sugar) and hydroxyl group (3’C of another sugar)

  • this releases 1 x H2O

  • forms a sugar-phosphate backbone

what are the 3 ends of DNA?

5’ end —> phosphate end of one sugar

3’ end —> --OH group of another sugar

What are the 2 types of bases? give examples

• purines = 2 rings

  • adenine, guanine

• pyrimidines = 1 ring

  • thymine, cytosine, uracil

Draw DNA

Compare and contrast DNA and RNA

DNA

• double helix

• the permanent genetic code

RNA

• variety of shapes depending on the type of RNA

• does not contain a permanent genetic code except in RNA viruses

How are the 2 strands of DNA joined together? Why is this important?

• complementary base pairing between N-bases

• this helps stabilise double helix

List some functions of the complementary base pairing rule

• Stabilises double helix

• maintains the accurate base sequence during DNA replication

• ensures the same protein is produced (same code) during geneexpression

The genetic code is used by who?

• all living organisms, meaning the same protein will be made no matter who translates it

How many bonds are formed in A,T,C,G?

• AT = 2 hydrogen bonds

• CG = 3 hydrogen bonds

Replication, transcription, translation all occur in which direction? why does direction matter?

• 5’ to 3’

• ensures the conservation of DNA base sequence so the same protein is produced

• also, enzymes can only attach in a certain direction

Why must A always pair with T, and C with G?

• If A binds with G, for example, the length is too long

• If T binds with C, the length is too short

• AT, CG complementary bonding is needed to stabilise DNA because the length of the base pairs is consistent

What form is eukaryotic DNA found in the nucleus? describe the structure

• as nucleosomes:

  • has DNA (Around 150 base pairs) wrapped around a core of 8 histones + H1 special histone (maintains shape) TWICE

  • nucleosomes are linked together, with DNA strand from one nucleosome going into the next nucleosome (this section is called DNA linker)

What is the relationship between nucleosomes and chromosomes?

• Chromosome > chromatin fibre > nucleosomes > double helix

• nucleosomes stack up and coil around other proteins in a very condensed shape called chromosomes

Why are nucleosomes important?

• Since eukaryotes have large genomes, nucleosomes help supercoil DNA while ensuring appropriate access to it

  • this helps fit it into the nucleus

  • DNA can be accessed when coils unwind and histones are removed so DNA can be copied/transcribed

Describe the hershey-chase experiment and the steps involved

• goal: prove that DNA makes up genetic material and not protein

• used T2 bacteriophage (virus that infects E. coli bacteria). The virus injects its DNA into bacteria cell while protein coat remains on outside

• used radioactive phosphorus (to label DNA) and sulfur (to label protein)

• conclusion: when bacteriophages with (³²P) infected non-radioactive bacteria, all the infected cells became radioactive. THe next generation of bacteriophages were all radioactive. When bacteria were infected with bacteriophages (³⁵S), no radioactivity was detected (since virus coats were removed)

  • thus: bacteriophages inject DNA into bacterial cell while protein component remains outside

What did Chargaff’s data prove?

• before: thought that DNA was single stranded and made from repeating units of tetranucleotides —> equal amounts of A, G, C, T

• Now: Chargaff analyzed DNA using paper chromatography to analyze relative concentrations of A, T, C, G

  • conclusion = amount of A = T, and amount of C = G

  • supported double helix model and about complementary base pairing

What type of reaction forms covalent bonds to create the sugar phosphate backbone?

• condensation

Compare and contrast ribose vs. deoxyribose

Ribose:

• C₅H₁₀O₅

• has 1 more oxygen than deoxyribose (a OH group at C2 instead of H)

Deoxyribose

• C₅H₁₀O₄

give 4 examples of nucleic acids

1. mRNA

2. tRNA

3. rRNA

4. ATP