Unit 4A - DNA Replication & Protein Synthesis

What did Griffith's experiment show?: Griffith showed that a "transforming factor" could transfer genetic traits between bacteria.

What did Hershey and Chase prove with their experiment?: They proved that DNA, not protein, is the genetic material that carries instructions for life.

Conclusion of Griffith and Hershey-Chase experiments:: DNA is the molecule responsible for heredity.

Structure of DNA:: Double-stranded, contains thymine, uses deoxyribose sugar, stores genetic information.

Structure of RNA:: Single-stranded, contains uracil, uses ribose sugar, helps build proteins using DNA instructions.

What are Chargaff’s rules?: A = T and C = G in DNA; supports complementary base pairing in the double helix.

Why can DNA replicate easily?: Its strands are complementary, so each strand can serve as a template for a new strand.

Where does DNA replication occur in prokaryotes and eukaryotes?: Prokaryotes: cytoplasm; Eukaryotes: nucleus.

Role of helicase in DNA replication:: Unzips the DNA by breaking hydrogen bonds.

Role of topoisomerase in replication:: Relieves twisting strain by breaking and rejoining DNA strands.

Role of primase in replication:: Lays down RNA primers to start new strand synthesis.

Role of DNA Polymerase III:: Adds DNA nucleotides to the growing strand (5’ to 3’ direction).

Leading vs. lagging strand:: Leading = continuous synthesis; Lagging = synthesized in Okazaki fragments.

Role of DNA Polymerase I:: Replaces RNA primers with DNA and proofreads the strand.

Role of ligase:: Seals the gaps between Okazaki fragments.

Simple steps of DNA replication:: Helicase unzips → Primase primes → Polymerase copies → Polymerase I replaces primers → Ligase seals.

What is the central dogma?: DNA → RNA → Protein (Watson & Crick).

Location, reactants, and products of transcription:: Nucleus (eukaryotes); Reactants: DNA, RNA polymerase, RNA nucleotides; Product: mRNA.

3 steps of transcription:: Initiation (promoter binding), Elongation (mRNA grows), Termination (RNA polymerase releases).

Location, reactants, and products of translation:: Cytoplasm at the ribosome; Reactants: mRNA, tRNA, amino acids, ribosome; Product: polypeptide chain.

3 steps of translation:: Initiation (start codon), Elongation (codon reading + amino acid linking), Termination (stop codon).

How is genetic code used to make proteins?: DNA is transcribed to mRNA; ribosomes read codons, and tRNAs bring amino acids to form a protein.

Where and how is mRNA made in prokaryotes?: In the cytoplasm by RNA polymerase, used immediately for translation.

How is eukaryotic mRNA processed before it leaves the nucleus?: Introns are spliced, a GTP cap is added to 5’ end, and a poly-A tail to the 3’ end.

What is the structure of tRNA?: Cloverleaf shape with an amino acid attachment site and an anticodon that pairs with mRNA.

Structure and function of ribosomes:: Made of rRNA and proteins; two subunits that read mRNA and link amino acids during translation.

How does translation begin?: The ribosome binds mRNA at the start codon (AUG); tRNA with methionine binds, and the ribosome assembles.

Steps for building a polypeptide chain:: Codon recognition → Peptide bond formation → Translocation of ribosome along mRNA.

Types of point mutations:: Silent (no change), Missense (wrong amino acid), Nonsense (stop codon).

Types of larger mutations:: Inversion (flipped bases), Duplication (extra copies), Deletion (missing sequences).

Causes of mutations:: Physical (UV, X-rays), Chemical (toxins), Biological (viruses), or errors in replication.

Consequences of mutations:: Can be silent, harmful (cause disease), or beneficial (evolutionary advantages).

What are bacteriophages?: Viruses that infect bacteria.

Lytic cycle of a virus:: Virus copies itself and bursts the host cell.

Lysogenic cycle:: Virus DNA hides in host DNA until activated.

What are emerging viruses?: New or rapidly spreading viruses.

What is transformation in genetics?: A cell takes in foreign DNA from its environment.

What is transduction?: A virus transfers DNA from one bacterium to another.

What is a plasmid?: Small circular DNA in bacteria used in genetic engineering.