Bio ch 17

Central Dogma

DNA → RNA → Proteins flow of information in cells

Gene Expression

Process where DNA directs protein synthesis

Ribosomes

Molecular machines for protein synthesis

Transcription

DNA to mRNA synthesis for protein production

Translation

mRNA to protein synthesis in ribosomes

Beadle & Tatum Experiment

Demonstrated one gene-one enzyme hypothesis

Genetic Code

Triplet codons specifying amino acids

Redundancy in Genetic Code

Multiple codons for most amino acids

Unambiguous Genetic Code

Each codon specifies only one amino acid

Start Codon

AUG specifies methionine and starts translation

Stop Codon

Codons signaling the end of translation

RNA Polymerase

Enzyme catalyzing RNA synthesis

Complementary RNA

RNA sequence matching the DNA template

Uracil

Base in RNA replacing thymine in DNA

Template-Directed Polymerization

RNA synthesis following DNA template

DNA Replication

Copying the entire DNA molecule

Ribosome

Cellular machinery for protein synthesis

Promoter

DNA sequence indicating the start of transcription

Transcription Factors

Proteins regulating RNA polymerase activity

Template Strand

DNA strand used for RNA synthesis

Coding Strand

DNA strand complementary to the template strand

RNA Processing

Modification of pre-mRNA in eukaryotes before translation

5' Cap

Modified guanine nucleotide at the 5' end of mRNA

Poly-A Tail

Long sequence of adenine nucleotides at the 3' end of mRNA

Nucleases

Enzymes that degrade nucleic acids

Eukaryotes

Organisms with membrane-bound organelles

Prokaryotes

Organisms lacking membrane-bound organelles

Telomeres

Protect the genome

mRNA Modifications

Facilitate export to cytoplasm, protect from enzymes, help ribosome attachment

Untranslated Regions

Ribosome unread regions

Introns

Noncoding stretches between coding regions

Exons

Regions expressed and translated into amino acids

RNA Splicing

Removes introns, joins exons for continuous coding sequence

Spliceosome

Complex of RNAs and proteins for splicing

snRNAs

RNA molecules in spliceosome, form snRNPs

Ribozymes

Catalytic RNA molecules acting as enzymes

Splice Zone

Recognizes exons and introns, mediates cleavage and ligation

Proteins

Enzymes, signaling, regulatory, structural molecules

Alternative Splicing

Produces multiple polypeptides from one gene

Isoforms

Proteins from same gene with different splicing

Proteome

Totality of proteins in an organism

Protein Domains

Regions encoding specific structure or function

Exon Shuffling

Results in new proteins through domain rearrangement

Transfer RNA (tRNA)

Carries amino acids, base-pairs with mRNA codons

tRNA Structure

80-nucleotide RNA strand with amino acid and anticodon ends

Anticodon

Base-pairs with mRNA codon

Wobble

Allows tRNAs to bind to multiple similar codons

tRNA Charging

Attaching amino acids to tRNAs by aminoacyl-tRNA synthetase

Aminoacyl-tRNA Synthetase

Enzyme attaching amino acids to tRNAs using ATP

Prokaryotic Ribosomes

Targeted by antibiotics to inhibit bacterial protein synthesis

Eukaryotic Ribosomes

Differ from prokaryotic ribosomes, not targeted by antibiotics

Ribosomal Subunits

Large and small subunits made of proteins and rRNA

Ribonucleoprotein Complex

Ribosome structure with rRNA and proteins

Translation Initiation

Starts at unique 5' cap and AUG start codon

Translation Elongation

Three-step cycle: codon recognition, peptide bond formation, translocation

Translation Termination

Occurs at stop codon, release factor adds water molecule

Polyribosomes

Multiple ribosomes translating same mRNA simultaneously

Gene Expression in Prokaryotes

Transcription and translation can occur simultaneously

Gene Expression in Eukaryotes

Transcription and translation are spatially separated by the nuclear envelope