UNIT 6: DNA

BIG IDEA: DNA contains the genetic information to produce proteins but must first be converted to RNA to do

so

http://evolution.berkeley.edu/evolibrary/article/mutations_02

Why do cells need DNA?

• DNA contains the information cells need to function and live.

• Two main roles for DNA are

1. Storing genetic info and to

2. “Read” and translated to make proteins

DNA Replication

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for

the genetic material”~Watson and Crick

Why do cells need to replicate (copy) their DNA?

• To make new cells and make sure all new cells have a complete set of the genetic info

How do cells replicate their DNA?

1. The DNA double helix is

unwound by an enzyme.

adds complementary nucleotides.

2. Another enzyme moves down the 2 original DNA strands and

3. Two separate DNA molecules are formed, each withone new strand and one old strand.

Replication Stats• 6 billion base pairs per cell.• All are replicated in a few hours. • Mistake happens one per billion

nucleotides.

Mistakes = Mutations• Mutations are changes in the base

sequence of the DNA molecules.• This can have serious affects on

genes and the functions of cells.• Cancer is caused by mutations in

DNA.

Mutagens

• Physical or chemical factor that increases the frequency of mutations.

• Examples: UV rays, X-rays, smoking

3 Types of Mutations

• Insertion• Deletion• Substitution

MUTATIONS

DO NOW:

• What words do you think of when you hear the term mutations?

Three Types

1. Substitute: one nitrogen base is substituted for another in the DNA strand

• Normal DNA:TAGCGCTAATCGCGAT

Mutated DNA:TAGCGCTAATCTCGAT

Three Types

• Insertion: One nitrogen base is inserted or added to a DNA strand

• Normal DNA:TAGCGCTA

ATCGCGAT

• Mutated DNA:TAGCGCTA

ATTCGCGAT

Three Types

3. Deletion: one nitrogen base is deleted from the DNA strand

• Normal DNA:TAGCGCTA

ATCGCGAT

Mutated DNA:

TAGCGCTA

ATCGCAT

Substitution Examples

Normal DNA: DNA with Mutation:AAA ATG CTT AAA ATG TTT

mRNA: mRNA:UUU UAC GAA UUU UAC AAA

Amino Acid: Amino Acid:Phe-Tyr-Glu Phe-Tyr-Lys

Create:

1. DNA strand with one base inserted

2. DNA strand with one base deleted

How does this effect amino acid sequence?

Chromosomal Mutations

• Deletion: loss of a piece of chromosome

Mutation Type 2 & 3

• Inversion: chromosomal segment breaks off, flips around backward, and reattaches

• Translocation: piece of one chromosome breaks off and reattaches to a nonhomologous chromosome

Mutation Type #4

• Nondisjunction- chromosome fails to separate from it homologue

Protein Synthesis

Transcription

DNA vs. RNA

• Single stranded

• Ribose sugar• Uracil• Anywhere

• Double stranded

• Deoxyribose sugar

• Thymine • Nucleus

3 Types of RNA

• Messenger RNA (mRNA): Carries information from DNA to ribosome for________________.

• Transfer RNA (tRNA): Transport _________________.

• Ribosomal RNA (rRNA): makes up the _____________.

protein synthesis

amino acids

ribosomes

Part 1:Steps of Transcription1. An _________ attaches to a section of

DNA, separating the two strands. 2. The enzyme moves down the DNA,

building a strand of RNA that is __________________ to the DNA.

3. The enzyme reads a ________ code and the new strand of RNA is completed and moves into the _______________.

enzyme

complementary

STOP

cytoplasm

Protein Synthesis

Translation

The genetic code• The base sequence is read in groups

of ____________________________. • Each 3-nucleotide sequence is called

a _________. • Each codon encodes for a specific

____________or a ______or ______signal.

three adjacent nucleotides

codon

amino acid start stop

Amino Acid

Anti-codon

Steps of Translation

1. mRNA attaches to a ____________. Amino acids floating in the cytoplasm are transported to the ribosome by _______.

2. The first tRNA binds to the ______ codon: AUG.

ribosome

tRNA

start

3. Another tRNA binds to the next codon and carries the appropriate amino acid. A __________________ forms between the two amino acids.

4. The first tRNA leaves and the ribsome moves across the next __________.

peptide bond

codon

5. Another tRNA binds to the codon and attaches the corresponding amino acid. The __________________ chain continues to grow.

6. Finally, the ribosome reads the ___________________, and the polypeptide falls off the ribosome.

http://www.wellesley.edu/Chemistry/chem227/nucleicfunction/translation/prtsynth.mov

polypeptide

STOP codon

Amino acid

tRNA

ribosome

mRNA

polypeptide

The final step of protein synthesis:

The polypeptide made at the end of translation, folds into the proper ________, becoming a functional ________.

shape

protein

The central dogma of biology

DNA RNA protein