DNA STRUCTURE & REPLICATION

WHAT IS DNA?

Organic molecule

Nucleic acid

WHERE IS IT

LOCATED? In the Nucleus Organized as chromosomes

DNA

STRUCTURE OF DNA

Made of nucleotides

Shaped like a twisted ladder

“Double helix” = two twisted strands

DNA STRUCTURE

Nucleotides have 3 parts:Deoxyribose sugarPhosphate groupNitrogen base

Two types of basesPurines

AdenineGuanine

PyrimidinesThymineCytosine

BASE PAIRING RULES:

cytosine-guanine (C-G)

adenine- thymine (A-T)

LADDER SHAPE (SIDES & RUNGS)

Sides: Phosphoric Acid Deoxyribose

Sugar Phosphoric AcidRungs: A-T T-A G-C C-G

WATSON & CRICK’S DOUBLE HELIX:

In 1953, James Watson and Francis Crick suggested the model for the structure of DNA.This shape is called a double helix.

WHAT IS DNA’S FUNCTION?Provide Hereditary Instructions

Provides the chemical code for every trait

Is a “blueprint” for making Proteins

DNA REPLICATIONCopying DNA

The number of chromosomes doubles

It occurs during Interphase (S)

2n to 4n2N

2N

STEPS FOR DNA REPLICATION:

1. DNA unzips Enzyme = helicase

2. Corresponding bases pair with the existing DNA strand

3. DNA reforms enzyme =

polymerase

4. 2 new strands twist into helix

IdenticalStrands

The cell makes them (from DNA

instructions).

Where do these Where do these new nucleotides new nucleotides come from?come from?

PROTEIN SYNTHESIS

DNA to ProteinCh 11.2

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REVIEW OF DNA REPLICATION DNA unwinds & unzips (helicase) Free nucleotides match with DNA nucleotides &

bond together (polymerase) Replicated DNA contains 1 original strand + 1 new

strand.

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GENES & PROTEINS DNA provides the instructions to

make proteins Different proteins have different

functions: Regulate cell functions Form cell structures like muscle

filaments, walls of blood vessels, and transport proteins

Enzymes control chemical reactions Proteins are made of amino acids Sequences of DNA nucleotides

contain information for assembling a chain of amino acids that make up a protein.

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RNA

A nucleic acid like DNA Different from DNA:

1. Single stranded2. Ribose sugar3. Bases:

Adenine (A) – Uracil (U)Guanine (G) – Cytosine (C)

Analogy: In a factory, DNA = instructions for building a car (proteins) and RNA = the workers who build it.

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TYPES OF RNA Messenger RNA (mRNA)

Brings information from the DNA in the nucleus to the cytoplasm

Found in the nucleus & cytoplasm Robosomal RNA (rRNA)

Makes up ribosomes, which clamp onto the mRNA and build protein

Found only in cytoplasm Transfer RNA (tRNA)

Transports amino acids to the ribosome to build a protein

Found only in cytoplasm

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TRANSCRIPTION

The process of making RNA from DNA:1. Enzymes untwist & unzip the DNA

(just like replication)

2. RNA nucleotides pair with complementary DNA nucleotides on one of the DNA strands

(Making mRNA)

3. Once base pairing is complete, mRNA breaks away and leaves the nucleus

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DNA Code

mRNAA

T

C

G

U

A

G

C

TRANSCRIPTION2

1

PROCESS OF TRANSCRIPTION

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THE GENETIC CODEThink of the genetic code as a

language: DNA and RNA are written in

the language of nucleotides (like letters in the English

alphabet)

Proteins are written in the language of amino acids(like characters in the Chinese

language)

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THE GENETIC CODE

Codon = each set of 3 nucleotides of mRNA that code for a specific amino acid

64 combinations of nucleotide codons are possible

The order of nucleotides determines the order of amino acids in a protein

Some codons give instructions AUG = start UAA, UAG, & UGA = stop

The genetic code is universal – all organisms use the same code.

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USING A CODON CHARTExamples:What amino acids are coded for by each of these:

1. AUG Methionine

(START)

2. CCG Proline (pro)

3. UAA STOP

4. GAC Aspartic

acid (asp)45

TRANSLATION

The process of converting the information of mRNA into a sequence of amino acids

Takes place in the ribosomes in the cytoplasm When mRNA leaves the nucleus and enters the

cytoplasm, ribosomes attach to it like clothespins on a clothesline. More than one ribosome at a time

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THE IMPORTANCE OF TRNA In order for proteins to be built,

amino acids need to be carried to the ribosomes.

Each tRNA molecule attaches to only ONE type of amino acid.

tRNA molecules contain anticodons that are complementary to mRNA codons

tRNA has the same

nucleotides but is has a different

shape for its function

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THE PROCESS OF TRANSLATION1. A ribosome attaches to mRNA2. tRNA molecules carry amino acids to the ribosome

and attach to the mRNA3. The ribosome slides down the mRNA to the next codon

○ The first tRNA leaves the ribosome

4. A new tRNA molecule carries another amino acid to the ribosome & enzymes join the two amino acids

5. The process continues and a chain of amino acids forms

6. When the ribosome reaches the stop codon, it detaches from the mRNA and the amino acid chain is released.

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We have a Protein !!!

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MUTATIONSMUTATIONS

WHAT ARE WHAT ARE MUTATIONS?MUTATIONS?

Changes in the nucleotide sequence of DNA

May occur in somatic cells (aren’t passed to offspring)

May occur in gametes (eggs & sperm) and be passed to offspring

ARE MUTATIONS HELPFUL OR HARMFUL?

Mutations happen regularly

Almost all mutations are neutral

Chemicals & UV radiation cause mutations

Many mutations are repaired by enzymes

ARE MUTATIONS HELPFUL OR HARMFUL?

Some types of skin cancers result from somatic mutations

Some mutations may improve an organism’s survival (beneficial)

TYPES OF MUTATIONS

CHROMOSOME MUTATIONS

Five types exist:DeletionInversionTranslocationNondisjunctionDuplication

CHROMOSOME MUTATIONS

May Involve:Changing the structure of a chromosome

The loss or gain of part of a chromosome

DELETION

Due to breakageA piece of a chromosome is lost

INVERSION

Chromosome segment breaks off

Segment flips around backwards

Segment reattaches

DUPLICATION

Occurs when a gene sequence is repeated

TRANSLOCATIONInvolves two chromosomes that aren’t homologous

Part of one chromosome is transferred to another chromosomes

TRANSLOCATION

NONDISJUNCTIONFailure of chromosomes to separate during meiosis

Causes gamete to have too many or too few chromosomes

Disorders:

CHROMOSOME MUTATIONS

Down Syndrome Chromosome 21 does

not separate correctly.

They have 47 chromosomes in stead of 46.

Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

CHROMOSOME MUTATIONS

Cri-du-chat Deletion of material on 5th

chromosome Characterized by the cat-like cry

made by cri-du-chat babies Varied levels of mental handicaps

SEX CHROMOSOME ABNORMALITIES

Klinefelter’s SyndromeXXY, XXYY, XXXYMaleSterilitySmall testiclesBreast enlargement

SEX CHROMOSOME ABNORMALITIES XYY Syndrome

Normal male traitsOften tall and thinAssociated with antisocial and behavioral

problems

SEX CHROMOSOME MUTATIONS

Turner’s SyndromeXFemalesex organs don't

mature at adolescence

sterilityshort stature

SEX CHROMOSOME MUTATIONS

XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility

CHROMOSOME MUTATION ANIMATION

GENE MUTATIONSChange in the nucleotide sequence of a gene

May only involve a single nucleotide

May be due to copying errors, chemicals, viruses, etc.

TYPES OF GENE MUTATIONS

Include:Point MutationsSubstitutionsInsertionsDeletionsFrameshift

POINT MUTATION

Change of a single nucleotide

Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

POINT MUTATION

Sickle Cell disease is the result of one nucleotide substitution

Occurs in the hemoglobin gene

FRAMESHIFT MUTATION

Inserting or deleting one or more nucleotides

Changes the “reading frame” like changing a sentence

Proteins built incorrectly

FRAMESHIFT MUTATION

Original:The fat cat ate the wee rat.

Frame Shift (“a” added): The fat caa tet hew eer at.

AMINO ACID SEQUENCE CHANGED

GENE MUTATION ANIMATION

REVIEW QUESTIONS

1. Where can mutations take place?2. What are the five types of mutations?3. What is nondisjunction?4. Name and summarize a genetic disorder.5. Explain how mutations are harmful and

beneficial to humans.