DNA Biology

Lab 11

Nucleic Acids

DNA and RNA both built of nucleotides containing Sugar (deoxyribose or ribose) Nitrogenous base (ATCG or AUCG) Phosphate group

Nitrogenous Bases

Nitrogenous bases can be double ringed purines or single ringed pyrimidines.

Nitrogenous Bases

A purine will always pair with a pyrimidine.

DNA

The phosphate group and sugar make up the backbone of the DNA molecule.

DNA

The DNA backbone Phosphate groups and pentose sugars

The 5' end of each strand has a free phosphate group attached to the 5' carbon of the pentose sugar.

The 3' end has a free hydroxyl group attached to the 3' carbon of the pentose sugar.

DNA

DNA consists of two complementary chains connected by hydrogen bonds. A=T C=G

DNA

DNA synthesis occurs in the 5' to 3' direction in both strands.

The DNA strands are antiparallel 5' end of one is

associated with the 3' end of the other.

The DNA ladder is twisted into a double helix Ten base pairs occur

per turn.

RNA

RNA exists as a single polynucleotide chain. Ribose Uracil

DNA Replication DNA must replicate itself

prior to cell division. Enzymes are responsible

for each step of replication, including proofreading.

The helix unwinds, separates, and each half acts as a template for the formation of a new complementary strand. Reaction catalyzed by

DNA polymerase.

Gene Expression

Gene expression – the use of information in DNA to direct the production of particular proteins. Transcription – first stage of gene

expression. A messenger RNA (mRNA) is synthesized from a gene within DNA.

Translation – second stage – mRNA is used to direct production of a protein.

DNA Coding DNA codes for

the sequence of amino acids in a protein.

A codon is three base-pairs long and is a segment of mRNA that codes for an amino acid.

Transcription

Messenger RNA (mRNA) transcribes the DNA and transports it out of the nucleus.

Transcription

Before leaving the nucleus, segments of mRNA called introns are removed and the exons are spliced together. Exons contain the information coding for the

protein that will be synthesized.

Translation

Translation occurs on ribosomes outside the nucleus.

mRNA attaches to a ribosome and protein synthesis begins.

Translation

Transfer RNA (tRNA) collects free amino acids from the cytoplasm and delivers them to the polysome (mRNA-ribosome complex) where they are assembled into a polypeptide. tRNA has a triplet – the

anticodon – that is complementary to the codon of mRNA.