Chapter 11

Nucleic Acid

Nucleic Acid

A long chain (polymer) made up of many nucleotides linked together

• DNA (Deoxyribonucleic acid)

• RNA (Ribonucleic acid)

Nucleotide

Is the basic building block (monomer) of nucleic acids

Purine

• Adenine (A)

• Guanine (G)

Pyrimidine

• Cytosine (C)

• Thymine (T)

• Uracil (U)

What are Nucleosides made of

Base + Sugar

What are Nucleotides made of

base + sugar + phosphate

How do we name nucleic acid for ribose

(Nucleoside) (prefix)phosphate

How do we name a nucleic acid for deoxyribose

Deoxy( nucleoside) (prefix)phosphate

Adenine (A)

Adenosine (A)

Guanine (G)

Guanosine (G)

Cytosine (C)

Cytidine (C)

Uracil (U)

Uridine (U)

Phosphodiester bond

Links nucleotides together to form nucleic acids; oxygen in phosphate group connected between the 3’ and 5’ carbons of sugar molecules

Primary Structure

Nucleotide sequence

• read from free 5’ end to free 3’ end

Secondary Structure

• Double helix

• backbone is antiparallel to each other

• one strand in 5’ to 3’ direction; other strand in 3’ to 5’ direction

• bases interact through hydrogen bonding

Complementary base pair in DNA

A-T and G-C

Teriary structure

• Supercoiling: further twisting of the DNA double helix structure

• DNA is wound around (supercoiled around) proteins - histones

• Histones pack together to form chromosomes

Complementary base pair in RNA

G-C and A-U

How many H-bonds does G-C make

3

How many H-bonds does A-T make

2

What is RNA

• Single stranded

• Usually much shorter than DNA strand

• Contains Uracil (U) instead of T

mRNA

• Transcription: the process of making a gene copy from DNA

• DNA double helix temporarily unwinds, complimentary copy is made from template strand

• Catalyzed by RNA polymerase

• Notice the 3’ and 5’ designations

• Contains codons

  • 3-letter segments

rRNA

• Ribosome made of rRNA and proteins

• small and large subunits bind mRNA for protein synthesis

tRNA

• facilitates translation

What does tRNA help do to mRNA

It helps to “decode” mRNA

Anticodon

three-base sequence, can hydrogen bond to complementary bases on mRNA. “Decodes” mRNA

Codon

Three-base sequence (triplet) that translates to a specific amino acid

Mutation

• any change in a DNA nucleotide sequence

• Amino acid is replaced with different amino acid (may affect structure and function of protein)

• Premature stop codon (terminates protein formation too soon)

• inserting or deleting a base. Messes up every codon downstream (frameshift mutation)

Silent Mutations

• Results in no change in protein sequence

  • EX: Codon CAU is changed to CAC- both code for histidine

• Change in protein sequence has very little effect on protein function

  • EX: Isoleucine (AUU) is changed to valine (GUU) - amino acids are similar in size and polarity

Spontaneous mutation

Error that occurs randomly when DNA replicates

Mutagen

• Environmental agents that produce mutations in DNA (chemicals, radiation, carcinogens, etc)

• Mutation in somatic cells only affects the individual organism

• Mutation in germ cells (egg or sperm) can be passed on to future generations - genetic diseases