DNA

Essential Question: How does the structure of the DNA molecule allow it to carry information?

Fun Website to Explore! http://learn.genetics.utah.edu/content/molecules/

DNA History

• Griffith – Experimented on mice and observed some harmless strains of bacteria could change into harmful strains. He called this transformation.

• Avery – Repeated Griffith’ experiment and discovered that DNA stores and transmits genetic information from one generation to the next.

http://nortonbooks.com/college/biology/animations/ch12a01.htm

More DNA History

• Hershey-Chase –Concluded that the genetic material in bacteria was DNA not proteins

• Watson & Crick –created the double helix model for DNA after viewing the work of Rosalin Franklin

Structure of DNA

• DNA is a polymer made up of

monomers called nucleotides.

– Backbone

• Deoxyribose Sugar and Phosphate

– Rungs of the ladder

• Nitrogenous bases

Nucleotides

• Monomers of the DNA molecule– Each nucleotide is

made up of three parts: • a 5-carbon sugar

called deoxyribose • a phosphate group • and 1 of 4 different

nitrogenous bases

Nucleotide Bonding in the DNA Molecule

• Nucleotide bonding– Covalent between the sugar,

phosphates and nitrogen base

– Hydrogen bonds between the bases of opposing nucleotides

– Nitrogenous bases can occur in any order

http://learn.genetics.utah.edu/content/molecules/builddna/

Nitrogenous Bases of Nucleotides

• 4 kinds

• Divided into two classes:

1) Purines

• 2 ring structure

• Adenine & Guanine

2) Pyrimidines

• 1 ring structure

• Thymine & Cytosine

Chargaff’s Rules – Base Pairing Rules

The proportion of :

• Adenine and Thymine is always the same

– Adenine always bonds with Thymine

• Cytosine and Guanine is always the same

– Cytosine always bonds with Guanine

• Question?– A DNA sample contains 28% Adenine– What are the %’s of Thymine, Guanine and

Cytosine?

Prokaryotes & DNA

• DNA is

– located in the cytoplasm

– a single circular molecule

Eukaryotes & DNA

• In Eukaryotes

–DNA is• 1000 x’s more than

prokaryotes

• located in the nucleus in the form of chromosomes

DNA Length

• Bacteria have about 1.6mm of DNA

– They are only 1.6µm in diameter

• Eukaryotes have over a meter of DNA in each cell.

– How do you stuff this all in a little cell?

DNA Packaging

• Chromatin consists of DNA and protein. • The DNA helix is wrapped around nucleosomes,

an octamer of histone proteins.

DNA Replication

• During DNA replication,

– DNA molecule separates into 2 strands

– each strand serves as a template

– new “complimentary” strands are built following the base pairing rules

• Process is “semiconservative”

• New DNA has one new strand and one original strand

How It Occurs

• DNA replication regulated by a series of enzymes– DNA polymerase is the main

enzyme

• Two jobs– Add nucleotides

– “proof read” the new strands

Replication Forks and Bubbles

• Locations where

– Nucleotides are added by DNA polymerase

– Strands separate for replication

DNA polymerase

Replication fork

Replication forkNewly made complementary strand (red)

original strand (blue)

Writing Complementary Strands

• If you start with this template strand

A T C T A A G

What is the sequence of bases on the complementary strand?

DNA

Essential Question: How does the structure of the DNA molecule allow it to carry

information?

Types of Nucleic Acid

DNA RNA

• Nucleotide

Sugar – Deoxyribose Ribose

Bases – A, T, G, C A, U, G, C

• Strands 2 1

• Polymer Types 1 3

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Transfer RNA (tRNA)

From Genotype to Phenotype

• Protein Synthesis– Process that converts genotype (gene make-up)

into phenotype (physical appearance)

• 2 Steps• 1. Transcription

literally means “to write out”

• 2. Translationliterally means “to change to another language”

Step 1 - Transcription

• genetic info in DNA is transcribed into a strand

of messengerRNA (mRNA)

– Occurs in the nucleus

– Regulated by

RNA Polymerase

Starting and Stopping mRNA

• DNA carries directions

– Promotors

• start signal for RNA polymerase

– Terminators

• stop signal for RNA polymerase

Making mRNA

• Chromosome coils loosen

• RNA polymerase (enzyme) – separates the 2 strands of DNA exposing base

pairs

– matches unattached RNA bases to their complement on the DNA strand

– Covalently bondsRNA nucleotides

Writing RNA Strands

• If you start with this DNA template strand

A T G T A C A G G

What is the sequence of bases on the mRNA strand?

Editing mRNA

• mRNA must be SPLICED

• Before leaving the nucleus– introns are removed (stay inside)

– exons are linked together (exported)

INTRONS – noncoding sections of nucleic acid

EXONS – code for proteins in nucleic acid

Alternative splicing allows for a

single gene to be used for more

than one polypeptide –

RECENT DISCOVERY

The Genetic Code

• “Language” of mRNA

– Read 3 bases at a time

– 3 bases = 1 codon = 1 amino acid

• AUGCGAUACUCGUGA

• AUGAGGUAUAGCUAA

Codons

• 64 possible codons for 20 amino acids

– 1 is the “start” codon

• AA – Methionine

– 3 are “stop” codons

• UGA, UAA, UAG

• Do not code for amino acids

From Genotype to Phenotype

Essential Question:

How does the structure of the DNA molecule allow it to carry information?

Step 2 - Translation

• The process of making proteins from mRNA

– Occurs in the cytoplasm

– Need 3 things

• mRNA, tRNA, ribosome,

free amino acids

Ribosomes

tRNA – carries amino acids

• RNA molecule that folds into a special structure

• Each tRNA carries one type of AA

• Each has a specific anticodon that matches the mRNA codon

Translation - Begins

• Setting up the RNA / Ribosome complex

– mRNA attaches to small ribosome subunit

– tRNA with Methionine attaches to mRNA

– Large ribosome subunit attaches

Translation - Elongation

• tRNA’s continue to bring in AA

• AA bond to one another and are released from the first tRNA

• Ribosome moves along the mRNA

• Process of growing the AA chain is called elongation

Translation - Stops

• Stop codons signal release factor

• Ribosome releases polypeptide, mRNA

Translation –A continuous process

Examples of protein functionsFunction Description Example

Antibody Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.

Immunoglobulin G

EnzymeEnzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.

Phenylalanine hydroxylase

MessengerMessenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.

Growth hormone

Structural component

These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.

Actin

Transport / storage

These proteins bind and carry atoms and small molecules within cells and throughout the body. Ferritin

Proteins can be described according to their large range of

functions in the body, listed in alphabetical order:

From Genotype to Phenotype

Essential Question:

How does the structure of the DNA molecule allow it to carry information?

12.4 Mutations

Unit Essential Question:

How does the structure of the DNA molecule allow it to carry information?

Mutations

• When mistakes are made during the copying of DNA it causes changes to the genetic material and potentially to the message

• 2 Major Types of Mutations

1) Gene Mutation

2) Chromosomal Mutation

Mutations• When mistakes are made during the copying

of DNA it causes changes to the genetic material and potentially to the message

• 2 Major Types of Mutations

1) Gene Mutation (impacts a single gene)

2) Chromosomal Mutation (impacts the whole chromosome)

Gene Mutations

• Point Mutations

– A change in a single DNA base can lead to a mutation in a single gene or a number of genes depending upon location

• 3 General Types

– Insertion

– Deletion

– Substitution may or may not cause a change

result in Frameshift Mutations

Point Mutations –Insertion and Deletion

• Insertions and deletions are referred to as Frameshift Mutations because they change the “reading frame” of the codons

Frameshift Mutations

Point Mutation - Substitution

• A single base is substituted

• Because of code redundancy, this sometimes results in no change to the amino acid sequence

• Therefore it may be a “silent” mutation

• Or can change the code to a STOP codon and fail to produce a protein and we call this a “nonsense” mutation

Mutations• When mistakes are made during the copying

of DNA it causes changes to the genetic material and potentially to the message

• 2 Major Types of Mutations

1) Gene Mutation (impacts a single gene)

2) Chromosomal Mutation (impacts the whole chromosome)

Chromosomal Mutations

• Changes in chromosomes can occur in 4 basic types

1) Deletion

2) Duplication

3) Inversion

4) Translocation

Polyploidy

• Sometimes ENTIRE sets of chromosomes are duplicated

• Most common in plants, but can be found in fish, insects, amphibians and reptiles

• Only one report in mammals – a rat species

• Triploids (3n) and Tetraploids (4n) are the most common forms

Daylily Tetraploids

• Larger flowers

• Taller plants

• Thicker flower stalks

ALL of these traits are desirable in the horticulture industry