AP Bio 1-2 Unit 6

S phase

Phase where DNA replication occurs in the cell cycle.

Conservative model

Parental strands conserve entirely, creating new molecules.

Semi-conservative model

Each daughter DNA contains one parental and one new strand.

Dispersive model

Daughter DNA contains a random mix of parental and new DNA.

Meselson and Stahl

Conducted experiment confirming semi-conservative DNA replication.

15N isotope

Heavy nitrogen used to label bacterial DNA in experiments.

14N isotope

Light nitrogen used after transferring bacteria for DNA analysis.

Origins of replication

Sites where DNA replication begins and forks form.

Helicase

Enzyme that unwinds DNA strands at replication forks.

Single strand binding proteins (SSBPs)

Proteins that stabilize unwound DNA strands during replication.

Topoisomerase

Enzyme that prevents DNA supercoiling ahead of replication fork.

Primase

Enzyme that synthesizes RNA primers for DNA replication.

DNA Polymerase III

Enzyme that adds nucleotides to growing DNA strand.

Leading strand

Synthesized continuously in the same direction as helicase.

Lagging strand

Synthesized in segments away from the replication fork.

Okazaki fragments

Short segments of DNA on the lagging strand.

DNA ligase

Enzyme that joins Okazaki fragments into a continuous strand.

Telomeres

Non-coding nucleotide sequences protecting DNA ends from erosion.

Telomerase

Enzyme that adds telomeres to the ends of DNA.

Mismatch repair

Process correcting errors in DNA base pairing.

Nuclease

Enzyme that removes damaged DNA segments.

Proofreading

Process where DNA polymerase checks for errors during synthesis.

3' to 5' direction

Direction in which DNA Polymerase III moves on parental strand.

5' end problem

Lagging strand cannot complete replication at 5' end.

Rosalind Franklin

Pioneered X-ray crystallography of DNA.

Edwin Chargaff

Discovered base pairing rules in DNA.

Chargaff's Rule

Adenine equals thymine; cytosine equals guanine.

Nucleotide

Building block of DNA, consisting of sugar, phosphate, base.

Purines

Double-ring structures: adenine (A), guanine (G).

Pyrimidines

Single-ring structures: cytosine (C), thymine (T), uracil (U).

Hydrogen Bonds

Hold base pairs together in DNA.

A-T Pairing

Adenine pairs with thymine via two hydrogen bonds.

C-G Pairing

Cytosine pairs with guanine via three hydrogen bonds.

Antiparallel Strands

One DNA strand runs 5' to 3', other 3' to 5'.

DNA Backbone

Composed of sugar-phosphate groups.

Double Helix

Three-dimensional structure of DNA discovered by Watson and Crick.

Eukaryotic DNA

Linear chromosomes located in the nucleus.

Prokaryotic DNA

Circular chromosomes found in nucleoid region.

Plasmids

Small, circular DNA molecules in prokaryotes.

Gene Exchange

Bacteria can share plasmids, enhancing survival.

Recombinant Plasmid

Plasmid with inserted gene of interest.

RNA

Single-stranded nucleic acid, contains uracil instead of thymine.

DNA vs RNA

DNA is double-stranded; RNA is single-stranded.

5' End

End of DNA with a free phosphate group.

3' End

End of DNA with a free hydroxyl group.

Genetic Information

Stored in DNA, passed to next generation.

Antibiotic Resistance

Genes located on plasmids, shared between bacteria.

Proteins

Polypeptides made from amino acids linked by peptide bonds.

Amino Acids

Building blocks of proteins linked by peptide bonds.

Gene Expression

Process where DNA directs protein synthesis.

Transcription

Synthesis of RNA using DNA information.

Translation

Synthesis of polypeptides using RNA information.

Nucleus

Cell organelle where transcription occurs.

Ribosome

Cell structure where translation occurs.

Messenger RNA (mRNA)

Carries genetic information from DNA to ribosomes.

Transfer RNA (tRNA)

Brings specific amino acids during translation.

Ribosomal RNA (rRNA)

Forms ribosomes and links amino acids together.

Template Strand

DNA strand used as a template for transcription.

Codon

Three-nucleotide sequence on mRNA coding for amino acids.

Triplet Code

DNA nucleotide sequence read in groups of three.

Reading Frame

Correct grouping of codons during translation.

Polyadenylation Signal

Sequence that triggers mRNA release during termination.

5' Cap

Modified guanine nucleotide added to mRNA's 5' end.

Poly-A Tail

Adenine nucleotides added to mRNA's 3' end.

Introns

Non-coding sequences removed during RNA splicing.

Exons

Coding sequences joined together during RNA splicing.

Alternative Splicing

Single gene coding for multiple polypeptides.

RNA Polymerase

Enzyme that synthesizes RNA from DNA template.

Promoter Region

DNA sequence where RNA polymerase binds to initiate transcription.

Termination Sequence

Signals the end of transcription in prokaryotes.

Transcription Factors

Proteins aiding RNA polymerase binding in eukaryotes.

64 Codons

Total combinations of nucleotides coding for amino acids.