DNA and

RNA

Chapter 12

Types of Nucleic Acids

• DNA (Deoxyribose Nucleic Acid)

• RNA (Ribose Nucleic Acid)

DNA Structure

•DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.

•A molecule of DNA is made up of millions of tiny subunits called Nucleotides.

Nucleotides are composed of:1. A sugar 2. A phosphate group3. A nitrogenous base

Nucleotides

Phosphate

Pentose

Sugar

Nitrogenous

Base

Nucleotides• The phosphate and sugar form the

backbone of the DNA molecule, whereas the bases form the “rungs”.

• There are four types of nitrogenous bases.

Nucleotides

A

Adenine

T

Thymine

G

Guanine

C

Cytosine

Nucleotides

• Each base will only bond with one other specific base.

• Adenine (A)• Thymine (T)

• Cytosine (C)• Guanine (G)

Form a base pair.

Form a base pair.

DNA is a molecule of nucleic acid that stores and transfers genetic information.

Nitrogenous Bases

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Chargaff’s Rule

• Percentages of guanine and cytosine and percentages of adenine and thymine are almost equal in any sample of DNA.

• A = T and C = G

Question

If 32% of the bases in a certain sample of DNA were thymine, what would be the percentages of adenine, cytosine and guanine?

DNA Replication

• DNA duplicating before a cell divides• A pairs with T and G pairs with C

In the diagram, the complementary strand would be:

GTAGGC

G

G

A

T

T

A

A

C

T

G

C

A

T

C

RNA• A messenger between DNA and

ribosomes

• “Decodes” the genetic message contained in the DNA molecule

3 Types of RNA:

• Messenger RNA (mRNA) - copies information from DNA and carries it to the ribosomes in the cytoplasm

• Ribosomal RNA (rRNA) - makes up the major part of the ribosomes

• Transfer RNA (tRNA) - carries amino acids to the ribosomes where the amino acids are joined to form a polypeptide

Transcription

• Information in a DNA molecule is transferred to an mRNA molecule (DNA RNA).

• Guanine pairs with Cytosine

• Adenine pairs with Uracil

• Thymine pairs with Adenine

Practice Transcribing DNA

CUAGGA

Translation

• Decoding mRNA into a chain of amino acids (RNA proteins)

• Groups of 3 RNA nucleotides, called codons are “decoded” into amino acids

TranslationSection 12-3

TranslationSection 12-3

DNA RNA

• Deoxyribose (sugar)• Double stranded• Nitrogenous bases:

– Guanine– Cytosine– Adenine– Thymine

• Ribose (sugar)• Single stranded• Nitrogenous bases:

– Guanine– Cytosine– Adenine– Uracil

Codon

• Three-nucleotide sequence on mRNA that codes for a single amino acid

The Genetic Code

The Genetic Code

Mutation

• Change in a DNA sequence that affects genetic information

Blueprint

• DNA is the blueprint of an organism

• DNA tells an organisms how to construct it self

Genetic Mutations

• Point Mutations – change involving one or a few nucleotides– Substitution of one base for another– Insertion or deletion of a base

• Frameshift Mutations – shifts the reading of the genetic message by inserting or deleting a nucleotide

Substitution InsertionDeletion

Genetic Mutations: Substitutions, Insertions, Deletions

Section 12-4

Chromosomal Mutationsinvolve a change in the number or structure

• Deletion – loss of chromosome

• Duplication – produce extra copies of parts

• Inversions – reverse direction of parts

• Translocations – part breaks off and attaches to another part

Deletion

Duplication

Inversion

Translocation

Chromosomal MutationsSection 12-4