DNA replication

Semiconservative replication

each daughter molecule will have one old strand “conserved” from the parent molecule and one newly made strand

Origin of Replication

where replication begins

Replication Bubble

where the strands separate

Replication fork

where the new DNA strands are elongating

Where is the 5’ end in Antiparallel

phosphate group

3’ end in Antiparallel

OH of deoxyribose (sugar)

Antiparallel definition

strands run in opposite directions

Topoisomerase

corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands; preventing tangling

Helicases

enzymes that unwind the double helix at the replication forks and unzip the DNA strands (break the hydrogen bonds between nitrogenous bases)

Single Stranded Binding Proteins (SSBPs)

bind to and stabilize single stranded DNA

The initial nucleotide strand is a short RNA ____

primer

Primase

starts an RNA chain from scratch (makes a primer) and adds RNA nucleotides one at a time using parental DNA as a template

Primer characteristics

short (5-10 nucleotides long) and the 3’ end serves as the starting point for the new DNA strand

DNA polymerases

cannot initiate synthesis of a polynucleotides; they can only add nucleotide to the 3’ end

How are new nucleotides added

as each nucleotide triphosphate joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate

A new DNA strand can only elongate in the __ to _ direction

5 to 3

Leading Strand

DNA polymerase synthesizes continuously moving toward the replication fork

Lagging Strand

synthesizes as a series of fragments called Okazaki fragments

Ligase

joins Okazaki fragments on the lagging strand together

Who proofreads newly made DNA

DNA polymerase

In mismatch repair of DNA…

repair enzymes correct errors in base pairing

How can DNA be damaged

exposure to harmful chemicals or physical agents such as cigarette smoke and X-rays

Is the error rate after proofreading repair zero

no

Sequence changes (mutations) are the source of ____ in which _____ operates

genetic variation, natural selection

Prokaryote chromosome structure

circular DNA molecules with a small amount of protein. The DNA is found in the nucleoid region

Eukaryotic chromosome structure

linear DNA molecules associated with a large amount of protein. Chromatin is found in the nucleus of eukaryotic cells

Histones

DNA winds around them to form chromosomes, compacting it to fit inside the nucleus

Heterochromatin

highly condensed chromatin, difficult to express these genes

Euchromatin

loosely packed chromatin