Unit 6 Topics 1-2

Rosalind Franklin

Performed X-ray crystallography revealing DNA's helical structure.

Edwin Chargaff

Discovered base pairing rules: A=T, C=G.

Nucleotide

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

Purines

Double-ring nitrogenous bases: adenine (A) and guanine (G).

Pyrimidines

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

Hydrogen Bonds

Weak bonds holding DNA base pairs together.

A-T Pairing

Adenine pairs with thymine via two hydrogen bonds.

C-G Pairing

Cytosine pairs with guanine via three hydrogen bonds.

Antiparallel Strands

DNA strands run in opposite directions, 5' to 3' and 3' to 5'.

Sugar-Phosphate Backbone

Structural framework of DNA, formed by sugar and phosphate.

DNA Replication

Process where DNA strands separate for copying.

Eukaryotic DNA

Linear chromosomes located within a nucleus.

Prokaryotic DNA

Circular chromosomes located in the nucleoid region.

Plasmids

Small, circular DNA molecules independent of chromosomal DNA.

Recombinant Plasmid DNA

Plasmid with inserted gene of interest.

Gene Exchange

Bacteria can share plasmids, enhancing survival traits.

Chargaff's Rule

In DNA, A equals T and C equals G.

RNA

Ribonucleic acid, single-stranded, with uracil instead of thymine.

DNA vs RNA

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

Base Pairing

Specific pairing of nitrogenous bases in DNA.

5' End

DNA end with a free phosphate group.

3' End

DNA end with a free hydroxyl group.

Chromosomal DNA

Main genetic material in both prokaryotes and eukaryotes.

Antibiotic Resistance

Ability of bacteria to survive despite antibiotic treatment.

MRSA

Methicillin-resistant Staphylococcus aureus, a resistant bacterial strain.

Gene Transmission

Transfer of genes between bacteria via plasmids.

Hydrogen Bond Role

Facilitates easy separation of DNA strands during replication.

Nucleotide Pairing

Specific pairing of nucleotides: A with T, C with G.

Genetic Information

Stored in DNA, passed to next generations.

Plasmid Manipulation

Laboratory technique to insert genes into plasmids.

Plasmid Functions

Contain non-essential genes beneficial in specific environments.

Nucleotide Structure

Composed of a sugar, phosphate group, and nitrogenous base.

S phase

Phase in cell cycle when DNA replicates.

Conservative model

Parental strands direct synthesis of new DNA.

Semi-conservative model

Each daughter DNA has one parental and one new strand.

Dispersive model

Daughter DNA contains random mix of parental and new DNA.

Meselson and Stahl experiment

Used isotopes to determine DNA replication model.

15N

Heavy isotope used in Meselson and Stahl's experiment.

14N

Light isotope used after transferring bacteria.

Origins of replication

Sites where DNA replication begins.

Replication fork

Y-shaped region where DNA strands separate.

Helicase

Enzyme that unwinds DNA strands at replication fork.

Single strand binding proteins (SSBPs)

Proteins that keep DNA strands separated during replication.

Topoisomerase

Enzyme that prevents DNA supercoiling ahead of replication fork.

Primase

Enzyme that adds RNA primers to initiate DNA synthesis.

DNA Polymerase III (DNAP III)

Enzyme that synthesizes new DNA strands in 5' to 3' direction.

Leading strand

Synthesized continuously towards the replication fork.

Lagging strand

Synthesized in fragments 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

Repeating sequences at DNA ends to prevent erosion.

Telomerase

Enzyme that adds telomeres to DNA ends.

Proofreading

Process by which DNA polymerase checks for errors.

Mismatch repair

Enzymes correct incorrectly paired nucleotides.

Nuclease

Enzyme that removes damaged DNA segments.

3' to 5' direction

Direction in which DNAP III moves along parental strand.

5' end problem

Lagging strand cannot fully replicate 5' end.

Complementary strand example

5'- ACGTAC- 3' pairs with 3'- TGCATG- 5'.

Leading strand primer

Requires only one primer for continuous synthesis.

Lagging strand primers

Requires multiple primers due to fragment synthesis.

Replication process

Involves unwinding, primer addition, and strand synthesis.

DNA synthesis foundation

Primers provide starting point for DNA polymerase.

Parental strands

Original DNA strands that serve as templates.

Daughter molecules

Newly synthesized DNA strands after replication.

Replication accuracy

Ensured by proofreading and mismatch repair mechanisms.

Supercoiling

Twisting of DNA that topoisomerase alleviates.