AP BIO: Molecular Genetics

Central Dogma

• flow of genetic information

• DNA (transcription) —> RNA (translation) —> protein —> trait

Messenger RNA (mRNA)

• nucleotides made in nucleus

• copies DNA + leaves through nuclear pores

• carries info for specific protein

Ribosomal RNA (rRNA)

• made inside nucleus

• associate w/ proteins to form ribosomes

• site of protein synthesis

Transfer RNA (tRNA)

• serves as link between mRNA + growing chain of amino acids

• facilitates protein synthesis by carrying amino acids to ribosomes

Transcription

• DNA nucleic acid language to RNA nucleic acid language

• makes mRNA

• enzyme: RNA polymerase

Promoter Region

• binding site before beginning of gene

• TATA box binding site

• binding side for RNA polymerase + transcription factors

Transcription Factors

• initiation complex

  • transcription factors bind to promoter region

    • proteins which bind to DNA (e.g hormones)

    • turn on/off transcription

  • triggers binding of RNA polymerase to DNA

mRNA Splicing

• post-transcriptional processing

  • primary transcript = pre-mRNA

  • mRNA splicing —> edit out introns

  • makes mature mRNA transcript

RNA Splicing Enzymes

• snRNPs (small nuclear ribonucleoproteins)

• located in nucleus + composed of:

  • small nuclear RNA + proteins

Spliceosomes

• several snRNPs

• recognize splice site sequence (intron)

mRNA Protection

• mRNA needs to be protected on journey from nucleus to cytoplasm — enzymes in cytoplasm attack mRNA

  • add 5’ GTP cap

  • add poly-A tail: longer tail, mRNA lasts longer = produces more protein

Translation

from RNA nucleic acid language to amino acid language

Start Codon

AUG, methionine

Stop Codon

UGA, UUA, UAG

Building a Polypeptide

• Initiation: brings mRNA together, initiator tRNA

• Elongation: adding amino acids based on codon sequence

• Termination: end codon

Protein Synthesis in Prokaryotes

• DNA in cytoplasm

• circular chromosome

• naked DNA

• no introns

Protein Synthesis in Eukaryotes

• DNA in nucleus

• linear chromosomes

• DNA wound on histone proteins

• introns vs. exons

Translation in Prokaryotes

• DNA in cytoplasm

• transcription + translation are simultaneous in bacteria

• no mRNA editing

• ribosomes read mRNA as it’s being transcribed

Mutation in Somatic Cell

• somatic = body

• mutation will NOT be passed onto next generation

• affects daughter cells + product of mitosis + can be cancerous depending on mutation

Mutation in Germline Cell

• will be passed onto next generation

• affects gametes

• after fertilization, all cells will be affected by mutation

Point Mutation

• single base is changed

• base substituted for another base

• 3 types: silent, missense, nonsense

Silent Mutation

• no amino acid change

• redundancy in code

Missense Mutation

changes amino acid

Nonsense Mutation

change to stop codon

Frameshift Mutation

• results in shift in reading frame — changes everything downstream

• two causes:

  • insertions: adding base(s)

  • deletion: losing base(s)

DNA Methylation

• methylation of DNA blocks transcription factors — no transcription

• attachment of methyl groups (-CH3)

• genes turned off

• nearly permanent inactivation of genes

Histone Acetylation

• unwinds DNA

• enables transcription — genes turned on

• attachment of acetyl groups (-COCH3)

RNA Interference

• small interfering RNA (siRNA)

• bind to mRNA… death tag for mRNA (triggers degration)

• causes gene slicing

  • post-transcriptional process — turns off gene = no protein produced

Protein Degradation

• ubiquitin = death tag

• proteasome = degradation

Operon

• genes grouped together w/ related function

• has promoter + operator

Promoter

• RNA polymerase binding site

• transcribed as one unit + single mRNA is made

Operator

DNA binding site of repressor protein

Repressor Protein

• binds to DNA at operator site

• blocks RNA polymerase

• blocks transcription

Inducible Operon

• functions in catabolic pathways

  • digesting nutrients to simpler molecules

• produce enzymes only when nutrient is available

• turned on by presence of specific molecule

Repressible Operon

• functions in anabolic pathways

  • synthesizing end products

• turned off by presence of specific molecule