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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.