DNA Replication

DNA Replication DNA must be copied (before

a cell divides)

The DNA molecule produces 2 IDENTICAL new complementary strands following the rules of base pairing:

A-T, G-C

• Each strand of the original DNA serves as a template for the new strand

The hydrogen bonds between base pairs are broken DNA replication begins at many specific sites The main enzyme responsible is DNA

Polymerase

How can entire chromosomes be replicated during Mitosis (S-phase)?

Figure 10.5A

DNA Replication

1. DNA unwinds (helicase)

2. DNA “unzips” (DNA Polymerase) 3. Free-floating

nucleotides base pair with the original strand of DNAParental DNA

DNA Template

New DNA

4. 2 identical DNA molecules are formed

1. Why is replication necessary?

2. When does replication occur?

3. Describe how replication works.

4. Use the complementary rule to create the complementary

strand:

A---?G---?C---?T---?A---?G---?A---?G---?C---?A---?G---?T---?

Replication Quiz

1. Why is replication necessary?So both new cells will have the correct DNA2. When does replication occur?During Mitosis.3. Describe how replication works.Enzymes unzip DNA and complementary nucleotides join each original strand.

4. Use the complementary rule to create the complementary

strand:

A---TG---CC---GT---AA---TG---CA---TG---CC---GA---TG---CT---A

Replication Quiz

DNA Transcription

DNA can “unzip” itself and RNA nucleotides match up to the DNA strand.

Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC acids.

Transcription produces genetic messages in the form of mRNA

RNApolymerase

RNA nucleotide

Direction oftranscription

Templatestrand of DNA

In transcription, DNA helix unzips

– RNA polymerase binds to DNA and separates strands

– RNA nucleotides line up along one strand of DNA, following the base-pairing rules

– single-stranded messenger RNA peels away and DNA strands rejoin

RNA polymerase

DNA of gene

PromoterDNA Terminator

DNAInitiation

Elongation

Termination

Area shownin Figure 10.9A

GrowingRNA

RNApolymerase

Completed RNA

– The DNA is transcribed into RNA, which is translated into the polypeptide

Figure 10.6A

DNA

RNA

Protein

TRANSCRIPTION

TRANSLATION

• The information constituting an organism’s genotype is carried in its sequence of bases

(1961) Watson & Crick proposed…

…DNA controlled cell function by serving as a template for PROTEIN structure.

3 Nucleotides = a triplet or CODON(which code for a specific AMINO

ACID)

AMINO ACIDS are the building blocks of proteins.

AMAZING DNA FACTS… DNA from a single

human cell extends in a single thread for almost 2 meters long!!!

It contains information equal to some 600,000 printed pages of 500 words each!!! (a library of about 1,000

books)