DNA and RNA

What does DNA look like?What are the elements that makeup DNA?

DNA Structure= String of nucleotides (sugar, phosphate, base)

*Adenine*Thymine*Guanine*Cytosine

• purines - adenine, guanine• pyrimidines - cytosine,

thymine

Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

 DNA Nucleotides

Francis Crick and James Watson (1953)

Twisted Double Helix

Hydrogen Bonds are the “glue” that keeps

the two strands together

Each strand of the helix is a chain of nucleotides

What holds the strands together?

Always Together….Great CoupleD

E

N

I

N

E

H

Y

M

I

N

E

U

A

N

I

N

E

Y

T

O

S

I

N

E

A & T G & C

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

KeyAdenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

 Structure of DNA

How is DNA organized in a chromosome?

Remember Chromatin??DNA tightly coiled around proteins forming Chromatin which pack together to form thick fibers.

What exactly is chromatin?

ONE nucleus of ONE human cell = more than 1 meter of DNA!!!

Chromosome

E. coli bacteriumBases on the chromosome

Prokaryotic Chromosome Structure

Section 12-2

Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

How can DNA use its double-stranded structure to its advantage for replication???

“Something Old…Something New”

DNA Replication When does this occur in the cell cycle?

1) Enzymes un-twist and unzip the molecule (break H bonds between base pairs).

2) Each strand serves as a template (something “OLD”)

3) Free nitrogen bases form bonds and make complementary strands (Something “NEW”)

Template

4) DNA Polymerase bonds the nucleotides and proofreads the molecule

 DNA Replication

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA vs. RNA RNA – also a long chain of nucleotides (5-

carbon sugar, phosphate group, nitrogenous base)

Differences:1. RNA sugar = ribose, instead of deoxyribose2. RNA – usually single-stranded3. RNA has uracil to replace thymine (so U

binds with A)

“Always United & Great Couple”

RNA is in charge of assembling Amino Acids into Proteins

From DNA(Gene) to Protein

rRNA - ribosomal RNA - location of protein synthesis uses tRNA to make proteins

The players:

DNA - sequences of nitrogen bases forms the genetic code

mRNA - messenger RNA - makes a copy of the DNA in the nucleus and brings it to the rRNA

tRNA - transfer RNA - reads the mRNA and brings specific amino acids to the rRNA

Step 1: Transcription = recording the message Occurs in nucleus New mRNA strand forms from one of DNA

strands (creating the message) Let’s Practice…

Transcription Practice

Transcribe the DNA molecule below:

ATTATCGCGTAATGCTAATAGCTAATAGCGCATTACGATTATCG

Template

AUUAUCGCGUAAUGCUAAUAGC

mRNA

transcript

RNADNA

RNApolymerase

Figure 12–14 TranscriptionAdenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

Step 2: Editing of mRNA

Introns are removed – non coding regions of the DNA molecule

Exons remain – sequences that will be expressed

Step 3: Translation = Protein Synthesis Occurs at ribosome tRNA reads mRNA which has message from

genetic code (DNA) Genetic code is read 3 letters at a time, so

each word is 3 bases long

Every 3 letters is a CODON

Each codon codes for a specific amino acid.

What does an Amino Acid do again? Helps make proteins!

• We need codons for Protein Synthesis (Translation)• They are like directions to make proteins

• Every set of directions tells you where to START and where to STOP

• We too have these, we call them the “start and stop codons”

Codons to remember…

START is always: AUG

STOP is always: UAA UAG UGA

Translation Explained

tRNA UAC mRNA AUGCGCAUAACGCAU

Start Codon

methionine

Alternate sequence:

There are 20 different amino acids to be coded for.

There are 64 possible codons.

Start codon

Stop codon

Figure 12–17 The Genetic Code

Translation Practice

Make a polypeptide (chain of amino acids) chain from the mRNA molecule

AUGAUCGCGUAUUGCUACUAG - mRNA

methionine-isoleucine-alanine-tyrosine-cysteine-tyrosine STOP

Figure 12–18 TranslationSection 12-3

Figure 12–18 Translation (continued)

Section 12-3

Mutations - changes in the DNA sequence Gene mutation- changes in a single gene

• Point Mutations - substitution of one nucleotide for another

• Frame Shift Mutations - shifting of the genetic code due to insertion or deletion of nucleotide

Chromosomal mutation changes in the entire chromosome (containing many genes)

Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Mutation AnalogyTHE FAT CAT ATE THE RAT

substitution THE FAT CAT ATE THE CAT *The letter “C” was substituted for the “R”

insertion THE FAT CAT ATE THE RAT THC EFA TCA TAT ETH ERA T

*Because the “C” was added, all other letters shifted down, thereby changing the amino acids that are made.C

Deletion THE F T CAT ATE THE RATTHE FTC ATA TET HER AT*Again, the amino acids will change b/c the “F” was removed

A

Mutation Practice

What will the new amino acid be if the 5th nucleotide is substituted with an adenine?

AUGA CGCGUAUUGCUACUAG - mRNAU

What will the new amino acid sequence be if a guanine is inserted between the 9th and 10th nucleotide ?

ASPARAGINE

GGUA = VALINE

When a mutation occurs…

If the amino acid sequence is stopped early (a STOP codon is reached) = Nonsense

If the amino acid sequence continues but the wrong amino acids are coded for = Missense

Putting it all together

What is the amino acid sequence that forms from the following DNA molecule? (DNA synthesis)

TACTACACCGTATAACAGGGCCTAGCAACT

Template

ATGATGTGGCATATTGTCCCGGATCGTTGA

(Transcription)DNA - TACTACACCGTATAACAGGGCCTAGCAACT

mRNA - AUGAUGUGGCAUAUUGUCCCGGAUCGUUGA

(Translation)

amino acid sequence

methionine-methionine-tryptophan-histidine-isoleucine-valine-proline-aspartic acid-arginine-stop