Regents Biology

Regents Biology

Regents Biology

Regents Biology

Regents Biology

Paired bases DNA structure

double helix 2 sides like a ladder

Bases match together A pairs with T

A : T C pairs with G

C : G

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Watson and Crick

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DNA Replication Replication is semi-conservative (one strand

is old, one strand new) Each strand serves as a template (or

pattern) for the new strand

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Copying DNA Matching bases allows

DNA to be easily copied

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Making new DNA Copying DNA

replicationDNA starts as a double-stranded

molecule matching bases (A:T, C:G)

then it unzips…

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Origins of Replication

Where DNA Replication starts

Differs between organisms Prokaryotes = 1 origin

of replication Eukaryotes = many

different origins of replication

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DNA replication Strands “unzip” at the weak bonds

between bases

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General Process of DNA Replication Step 1: Initiator Proteins

Bind to origins of replication to begin replication

Attracts other enzymes involved in replication process

Step 2: DNA Helicase separates the DNA

helix

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DNA replication

DNA polymerase

Enzyme DNA polymerase adds new bases

DNA basesin nucleus

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Step 3: Primase Builds a primer at the 5’ end of the new DNA strand

Step 4 :DNA Polymerase III builds the new strand of DNA in the 5’ to

3’ direction

3’ 5’5’

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- Nitrogenous bases are located in the cytoplasm

- They enter the nucleus through the pores in the nuclear membrane

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DNAPolymerase

Copying DNA Build daughter DNA

strand use original parent

strand as “template” add new matching

bases synthesis enzyme =

DNA polymerase

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Problem… How can both strands of DNA be

replicated in a 5’- 3’ direction at the same time if they are antiparallel?

Answer: leading and lagging strands

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Leading and Lagging Strands

Leading strand is synthesized continuously in the direction of replication (goes in the same direction as helicase)

Lagging strand is synthesized in short fragments the opposite direction of replication (opposite direction as helicase)

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DNA Ligase

DNA Ligase Forms covalent bonds between

nucleotides to create a continuous strand of DNA

When DNA Polymerase I edits the DNA strand, DNA Ligase attaches the bases on one side of the DNA strand together.

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DNA Ligase

DNA Ligase seals Okazaki fragments together Forms covalent bonds between

nucleotides to create a continuous strand of DNA

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Thymine is added accidentally.

DNA polymerase cuts the damaged DNA.

The proper base is added.

Ligase joins the two spots.

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New copies of DNA Get 2 exact copies of DNA to split

between new cells

DNA polymerase

DNA polymerase

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Copied Chromosomes

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DNA Replication Replicate the following DNA strand:

A – G – G – C – T – T – C – A – G – T T – C – C – G – A – A – G – T – C - A

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