The Components and The Components and Structure of DNAStructure of DNA

• Structure: Deoxyribonucleic acid

• Found in all living things

• DNA strands were twisted around each other like the coils of a spring, a shape known as a double helix.

• A double helix looks like a twisted ladder or a spiral staircase.

Double HelixDouble Helix

How could DNA, or any other molecule, do the How could DNA, or any other molecule, do the three critical things that genes were known for? :three critical things that genes were known for? :

1. Genes had to carry information from one generation to the next.

2. Put the information to work by determining the heritable characteristics of organisms.

3. Be easily copied, because all of the cell’s genetic information is replicated every time a cell divides.

NucleotidesNucleotides• DNA is a long molecule made up of units called nucleotides.

Each nucleotide is made up of three basic components:

1. 5-Carbon sugar called deoxyribose

2. Phosphate group

3. Nitrogenous base

Bonds in DNABonds in DNA1. Nucleotides are held

together by covalent bonds

• 2. Hydrogen Bonds: 2 bases make up the “rungs” of the double helix and this is the bond they are held together by.

S P

B Covalent bonds

• Purines: made of 2 carbon rings• Adenine (A) & Guanine (G)

• Pyrimidines: made of 1 carbon ring• Cytosine ( C) & Thymine

(T)

4 Kinds of Nitrogenous Bases4 Kinds of Nitrogenous Bases

Base Pairing RulesBase Pairing Rules

• Adenine only bonds to Thymine

(A) = (T)• Guanine only bonds with Cytosine

(G) = (C)

FunctionsFunctions• The function of

DNA is to store and transmit genetic information that tells cells which proteins to make and when to make them.

MatchingMatching • 2 sides of DNA are complementary to one another.

• If you know one side of the helix you can figure out the other side.

• TACGTCGTA• ATGCAGCAT

Replicate DNAReplicate DNA1. DNA “unzips” at

one end by breaking up the hydrogen bonds between bases

2. Free floating nucleotides pair with the open bases on each side of the double helix.

3. Continues until DNA double helix “unzips” and 2 double helixes are made. Each double helix has one new strand and one old strand. Both are identical to each other and to the original.

RNARNA

• Ribonucleic acid• Single strand no double helix• Made of repeating monomers

called nucleotides

NucleotidesNucleotides Each nucleotide consists of 3 parts:

1. 5-Carbon sugar called ribose

2. Phosphate group

3. Nitrogenous base

• Purines: Adenine (A) & Guanine (G)

• Pryimidines: Cytosine ( C) & Uracil (U)

4 Types of Bases4 Types of Bases

Base Pairing RulesBase Pairing Rules

• Adenine only bonds to Uracil(A) = (U)

• Guanine only bonds with Cytosine(G) = (C)

In RNAIn RNA

Messenger RNA (mRNA)Messenger RNA (mRNA)

• 3 nucleotide bases on RNA are called a codon

• Holds genetic info from a DNA strand and translated into protein.

3 Types of RNA3 Types of RNA

Transfer RNA (tRNA)Transfer RNA (tRNA)

• Each tRNA bonds only to specific amino acids

• Has location called the anticodon, a 3 nucleotide base sequence.

3 Types of RNA3 Types of RNA

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

• Makes up a ribosome• “reads” the mRNA strand

3 Types of RNA3 Types of RNA

• For a cell to make a protein, the information from a gene is copied, base by base, from DNA into new strands of mRNA. The mRNA travels out of the nucleus into the cytoplasm, to ribosomes. mRNA directs assembly of amino acids that fold into completed protein molecules.

Genetic CodeGenetic Code

• Proteins are made of amino acids• 20 known amino acids• Sequence of nucleotides (bases) on

DNA determines what amino acids are put into proteins.

How many nucleotides (bases) are How many nucleotides (bases) are used to code for each amino acid? 3used to code for each amino acid? 3

• Read 1 base=at most only 4 combinations• Read 2 bases=at most only 16 combinations• Read 3 base=at most only 64 combinations

• 3 bases must be read at one time to code for 1 amino acid

• A 3 base sequence found on an mRNA is called a codon

• 60 combinations of 3 bases code just for amino acids

• 1 combination codes for a start as well as an amino acid. (AUG-Methionine). Methionine is the only amino acid specified by just 1 codon, AUG.

• 3 combinations code for a stop codon. The stop codons are UAA, UAG, and UGA. They encode NO amino acid. The ribosome passes ad falls off the mRNA .

TranscriptionTranscription

• Process where part of DNA double helix (a gene) is “read” and a strand of mRNA is created.

StepsSteps

1. DNA double helix “unzips” down the center between the bases at a certain location of the helix.

2. One side of the double helix is “read” starting at a certain base and “read” to a certain base (gene)

3. A complementary strand of mRNA is created.

4. DNA double helix “zips” back up.

5. Strand of mRNA leaves the nucleus.

TranslationTranslation

• Process where a mRNA strand is “read” and a protein is produced.

StepsSteps

1. A ribosome (which is made of rRNA) attaches to the strand of mRNA at a certain spot (AUG-start codon)

2. Ribosome reads the first 3 bases (called a codon) on the mRNA strand.

3. A tRNA that has an anticodon, that is a complement to the codon being read, attaches to the mRNA. Remember that tRNA’s have an amino acid attached to them

Ex. Codon(on mRNA)- AUG

Anticodon(on tRNA)= UAC

4. The tRNA leaves the rRNA but leaves the amino acid

5. Ribosomes reads the next codon on mRNA.

6. Repeat steps 3-5 until the certain codon is read called the stop codon.

7. Ribosome lets go of the mRNA strand.

8. All the amino acids that were brought by the tRNA are linked together producing a protein.

9. (Practicing)

DNA mRNA strand Protein

MutationsMutations

• Most are minor• Many are

harmful• Some are lethal• Very few are

helpful

Types of MutationsTypes of MutationsI. Point Mutations- changes

involving one nitrogen base

A. Frameshift Mutations- that Addition or Deletion of a nitrogen base, causing the gene sequence to read out of sequence

Types of MutationsTypes of Mutations

1. Insertion- Ex. ACG/TAG/GTA

ACG/TTA/GGT/A

2. Deletions: A piece of chromosome breaks off and is lost

Ex. ACG/TAC/GTA

ACG/TACG/TA

B. Base Substitution-

Ex. ACG/TAC/GTA

ACG/TAA/GTA

Types of MutationsTypes of MutationsII. Chromosome Mutations-

Involve segments of DNA

A. Inversion: Reinsertion of a sequence backwards

EX.

AGCTAGCTA AGGATCCTA

Types of MutationsTypes of MutationsB. Translocation- A piece

of a different chromosome is added to another

EX.AGCTAGCTA AGCTAGCTATCCAG