C8. Nucleic Acids

April 7th

DNA

• DNA = DeoxyriboNucleic Acid

• DNA is a polynucleotide

• Nucleotide = phosphate group, pentose sugar and an organic base

• Bases: A, D, T, G (Data Booklet)

• Sugar-phosphate backbone

• The structure is -helix

• The bases pair with H-bonds: A-T and D-G

• Function: Stores genetic information

Note the number ofH bonds:

Three for CC--GGTwo for AA--TT

Two strands:Each with S-P backbone

and bases as side groups

-helix:S-P outsideBases inside the helix

The hydrogen bonds in DNA

The genetic code• Gene is a segment of DNA that directs the

synthesis of a single polypeptide• Genetic code is a sequence of nucleotide

in triplet. Each triplet is called codon.• 64 codon exist in humans• 61 of the codons mean amino acid.• Example: GUU = valine amino acid.• The genetic code determines the order

and types of amino acids in protein synthesis.

RNA, Ribonucleic acid• Smaller than DNA• Structure is similar to DNA except:

– uracil (U) instead of thymine (T)– D-Ribose sugar instead of 2-deoxy-D-ribose– Single stranded

• Different types of RNA:– mRNA, messenger RNA– tRNA, transfer RNA– rRNA, ribosomal RNA

• Role: Translates the genetic information from DNA in protein synthesis

DNA and mRNA (transcription)

Protein synthesis

• Division of cell: The DNA code is duplicated, the new cell is a complete copy

• Replication: Copies of DNA made when a cell divides. Occurs in the nucleus.

• Transcription: Genetic messages in DNA are read and copied. Used to synthesise RNA in a nucleus.

• Translation: RNA directs protein synthesis in cytoplasm

• Read more here

Replication

Translation

Translation (animation)

DNA profiling• DNA profiles are like fingerprints, unique for each

person• Used when crimes are investigated• All cells from an organism creates same DNA• Sample from blood, semen, saliva, hair• DNA is broken down in small fragments by

enzymes.• Coded triplets and areas with no code.• Separated with electrophoresis• Radioactive 32P and X-rays are used for analysis

ExampleSuperman is married to Lois Lane and they have a young son named Johnny. Lately Superman has begun something is amiss with Johnny because he can find his way in the dark and he has a tendency to hang upside down from light fixtures or dark corners of the ceiling. Superman begins to suspect that Lois may have had a fling with her old boyfriend, Batman. Superman gets a court order for a blood sample from himself, Lois, Batman and Johnny. The DNA in each blood sample is amplified (increased is quantity via PCR). The DNA in each blood sample is then cut using restriction enzymes and the DNA fragments are placed in separate chambers of a sheet of gel in an electrophoresis chamber. After an electrical current has been run through the gel, you, the famous paternity judge, view the evidence on the electrophoresis gel (See next slide).

Who is the father of Johnny?

Example – Electrophoresis results

Example cont.

The fragments on Johnny's profile should be a mixture of the profiles of his 2 parents. It should be fairly evident that the fragments or lines for Lois and Batman are most similar to those of Johnny. The profile for Superman is not very similar to that of Johnny.

Thus, Batman is most likely Johnny's biological father!

Reference