DNA Biology

1
DNA Biology

• Lab 11

2
Nucleic Acids

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

3
Nitrogenous Bases

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

4
Nitrogenous Bases

• A purine will always pair with a pyrimidine.

5
DNA

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

6
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.

7
DNA

• DNA consists of two complementary chains
  connected by hydrogen bonds.
• AT
• CG

8
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.

9
RNA

• RNA exists as a single polynucleotide chain.
• Ribose
• Uracil

10
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.

11
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.

12
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.

13
Transcription

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

14
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.

15
Translation

• Translation occurs on ribosomes outside the
  nucleus.
• mRNA attaches to a ribosome and protein synthesis
  begins.

16
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.