DNA - Transcription, Translation, and Mutations

DNADNA Two strands coiled called

a double helix Sides made of a pentose

sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds

Center made of nitrogen bases bonded together by weak hydrogen bonds

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DNA Double HelixDNA Double Helix

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

Antiparallel StrandsAntiparallel Strands

One strand of DNA goes from 5’ to 3’ (sugars)

The other strand is opposite in direction going 3’ to 5’ (sugars)

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DNADNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Synthesis Phase (S Synthesis Phase (S phase)phase) S phase during interphase of

the cell cycle Nucleus of eukaryotes

Mitosis-prophase-metaphase-anaphase-telophase

G1 G2

Sphase

interphase

DNA replication takesDNA replication takesplace in the S phase.place in the S phase.

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DNA ReplicationDNA Replication

Begins atBegins at Origins of ReplicationOrigins of Replication Two strands open forming Two strands open forming

Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)

New strands grow at the forksNew strands grow at the forks

ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

3’

5’

3’

5’

Proofreading New DNAProofreading New DNA

DNA polymerase initially makes DNA polymerase initially makes about about 1 in 10,0001 in 10,000 base pairing base pairing errorserrors

EnzymesEnzymes proofread and correct proofread and correct these mistakesthese mistakes

The new error rate for DNA that The new error rate for DNA that has been proofread is has been proofread is 1 in 1 1 in 1 billionbillion base pairing errors base pairing errors

DNA Damage & DNA Damage & RepairRepair Chemicals & ultraviolet radiation

damage the DNA in our body cells Cells must continuously repair

DAMAGED DNA Excision repair occurs when any of

over 50 repair enzymes remove damaged parts of DNA

DNA polymerase and DNA ligase replace and bond the new nucleotides together

The Code

Experiments during the 1960s demonstrated that the DNA code was a three-base code.

The three-base code in DNA or mRNA is called a codon.

DNA, RNA, and Protein

Central Dogma

DNA is copied as RNA – Transcription RNA uses U

instead of T RNA is read to

make proteins – Translation Read by using

the reverse of RNA, similar to DNA’s 2nd strand

Translation In translation, tRNA

molecules act as the interpreters of the mRNA codon sequence.

At the middle of the folded strand, there is a three-base coding sequence called the anticodon. Each anticodon is complementary to a codon on the mRNA.

DNA, RNA, and Protein

Activity The first number tells you where the mutation starts,

followed by the number or what is deleted Ex: 487del7 means starting at base 487 7 bases

are deleted.

What Are Mutations?What Are Mutations? Changes in the nucleotide

sequence of DNA May occur in somatic cells

(aren’t passed to offspring) May occur in gametes (eggs &

sperm) and be passed to offspring

Chromosome Mutations

Five types exist:DeletionInversionTranslocation (don’t worry)Nondisjunction (don’t worry)Duplication

DeletionDue to breakageA piece of a chromosome is lost

InversionChromosome segment breaks off

Segment flips around backwards

Segment reattaches

DuplicationOccurs when a gene sequence is repeated