Molecular GeneticsBWET Summer Program in Environmental Science

Nucleotides

Pentose Sugars

Nucleotides BasesPurines: two carbon rings

Nucleotides BasesPyrimidines: single carbon rings

Polymerization of Nucleotides

Polynucleotides (Nucleic Acids)

TheDouble Helix

Base Pairing in DNA

Base Pairing in DNA

DNA Replication

DNA Replication

DNA Replication Two new strands, each made of one template strand and one new strand.

Strand Polarity in Complimentary Strands of Double-Stranded DNA

Adding NucleotidesAdd to 3 end of new strand (begin at 5 of template strand)

DNA Replication3 end5 end3 end5 end

DNA Replication

DNA Replication

DNA Replication

PCR: Amplification of DNA

Gene Expression

Polypeptides and ProteinsMolecules composed of linear arrangements of amino acidsIt is the sequence of these amino acids that determines the properties of a particular polypeptide or protein

Proteins differ according to their order of amino acidsProtein 1Protein 2

Steps of Gene ExpressionTranscriptionTranslation

Transcription and TranslationTranscriptionTranslationDNAmRNAprotein

Decoding DNAThe first step of decoding the genetic message is to copy the nucleotide sequence from DNA to RNA

RNAActs like a disposable copy of DNA for making proteinControls the assembly of amino acids into protein

Same nucleotides as DNAA single-strand of nucleotidesContains URACIL instead of THYMINE

Types of RNAThree types: Messenger RNA (mRNA)Ribosomal RNA (rRNA)Transfer RNA (tRNA)

Each plays a different role in the assembly of amino acids into protein

mRNAMessenger RNAA direct copy of the DNA but using UracilActs as a messenger from the DNA to the rest of the cellbase sequence reflects that of a gene that specifies the amino acid sequence of a protein

rRNARibosomal RNARemember, proteins are assembled ON ribosomesThe rRNA is found attached to the ribosomes where the proteins are assembled

Ribosomelarge subunitsmall subunitfunctional ribosome

tRNA Transfer RNAA type of RNA that collects the necessary amino acids and escorts them to the assembly site on mRNA

Structure of tRNA

Gene Expression: Transcription- Involves the copying of the genetic code into a molecule of messenger RNA (mRNA)Only copies the area of interest in the DNA strandIn the eukaryotic cell, transcription occurs in the nucleus. Prokaryotes dont have a nucleus.Base pairing rules apply except that uracil replaces thymine in RNA

Location: In the NucleusRNADNARNA polymeraseAdenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)All of Transcription (making mRNA) in eukaryotes takes places in the nucleus

Only unwinds segment that codes for a certain proteinRNA Polymerase add complementary bases

Base Pairing in DNA

Base Pairing in RNA

The mRNA strand turns out the same as Sense Strand, except for Us instead of Ts

Transcription

Gene Expression: Translation

Involves reading the triplet codons of the mRNA to determine the sequence of amino acids in a proteinThree stages: initiation, elongation, and terminationOccurs in the cytoplasm of all cells

Translation

The Nature of the Genetic CodeA sequence of three consecutive nucleotide bases codes for an amino acid in a proteinThere are 64 possible combinations of a triplet code that draws from four different letters (bases)

CodonThere are 20 different possible amino acids to make from different codons3 possible stop codon1 start codon TAC on DNAAUG on RNA

Codon ChartStart Codon

Codon Chart

Translation

Translation

Translation

Translation

Translation

Translation

Translation

Summary of Transcription and Translation

Summary of Transcription and Translation