chapter 12 dna. the secret of life dna: the genetic material
TRANSCRIPT
CHAPTER 12
DNA
Think Back…
Gregor Mendel and inheritance… Factors that determine traits are passed down from
generation to generation, they come from both mom and dad
But where did this information come from, and where was it stored?
Scientists knew there were both proteins and nucleic acids (DNA) in the nucleus of cells
Left scientists wondering what molecule was involved in inheritance – DNA or proteins?
Discovery
Griffith: found that one strain of bacteria could be transformed into another Created the search for the transforming substance.
Avery: identified the transforming molecule Scientists were still skeptical
Hershey & Chase: experiments provided definitive evidence that DNA was the transforming factor After these discoveries, scientists were more confident
that DNA was the transforming factor
The Scandal
Rosalind FranklinX-Ray Diffraction: Rosalind Franklin
used this method to discover the double helix structure
Other scientists stole this work, and used it to take credit for themselves, this later won them a Nobel Prize
WAIT!
Remaining questions – How do nucleotides come together to form DNA? How does DNA communicate information? How does DNA store information? How does DNA duplicate itself?
So we found it, but…
WHAT IS IT!?Genetic material!Blueprint for living organisms!Passed from generation to generation!DNA: Deoxyribonucleic AcidClassified as a nucleic acid, made up of
millions of tiny subunits called nucleotides
Nucleotides
NUCLEOTIDESMade of a
1. sugar (deoxyribose)2. a phosphate3. a nitrogenous base
REMEMBER!
A nucleotide is made ofSugar
PhosphateBase
Double Helix
The phosphate of one group bonds to the sugar of another
The phosphate and sugar form the backbone of the DNA molecule Like the “sides” of a
ladderThe bases form the
“rungs” 4 types of bases
Bases
Guanine (G)Adenine (A)Cytosine (C)Thymine (T)Each base will only bond
with 1 other specific base A – T C – G
Complementary base pairing the order of the bases in
one strand determines the order of the bases in the other strand
Hydrogen Bonds
Each pair is held together with a hydrogen bond A – T: two hydrogen
bonds C – G: three hydrogen
bonds
2) Four Bases (Attached in Pairs)
1) A Sugar Phosphate Backbone
DNA
In prokaryotic cells, DNA is a loop in the cytoplasm
Eukaryotic DNA is organized into individual chromosomes in the nucleus The length of a chromosome
can be 51 million to 245 million base pairs!
And remember, each of your cells has a copy of ALL that DNA!!!!
DNA makes up GENES which make up CHROMOSOMES found in the NUCLEUS of the CELL
K’NEX
Following the directions on your handout, build your model
Complete labeling sheet and crossword if not done
DUE tomorrow
SUGAR
DOUBLE HYDROGEN
TRIPLE HYDROGEN
ADENINE
CYTOSINE
GUANINE
THYMINE
PHOSPHATE
NUCLEOTIDE
12.2
DNA Replication
DNA Replication
Remember – every cell in your body has a copy of your DNA
But, that DNA in the cell must be copied first so that the new cells (remember you get 2 new daughter cells from one parent in mitosis) get a copy of the old DNA.
How does it get there? DNA replicates during interphase of mitosis and
meiosis
DNA Replication
The double helix structure helps explain how DNA copies itself
DNA replicates by making a strand that is complementary to the original strand
The double helix separates, acts as a template, and creates a new strand Unwinding Base pairing Joining
DNA Replication
The “parent strand” has two complementary strands
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.
Unzip
The first step is to “unwind” the parent strand
DNA helicase: enzyme responsible for unwinding and unzipping the double helix.
Hydrogen bonds are broken and there are two single strands
Template
Free Floating nucleotides (in the nucleus) match up to the parent strands of DNA
DNA polymerase adds new nucleotides to the single strands and proofreads before creating two new identical strands
DNA, RNA & Proteins
DNA
DNA is a codeThe nitrogen bases spell out a message that
creates proteins Proteins then make up the organism!
The Code
It’s like A, T, C, and G are the only letters in the alphabet - You can use them as many times as you’d like and
in any order to make “words” These combine to make “sentences” The “sentences” combine to make “paragraphs” The paragraphs give instructions to the nucleus
to make a living organism and all its unique traits
The Central Dogma
How does DNA act as a code for protein synthesis?
Amino acids make up proteins and proteins act as building blocks for cells and enzymes
Central Dogma: DNA is TRANSCRIBED
into RNARNA is TRANSLATED
into proteins
Ribonucleic Acid
Nucleic acid, single strandContains sugar riboseHas Uracil instead of
Thymine A – U C – G
Messenger protein (mRNA), carries the DNA to ribosomes
Translates DNA Think of DNA as written in
French, the RNA must translate it into English so the body can use it
The Code
DNA is a 3 base (nitrogen) code3 nitrogen bases in a strand of DNA code for
1 amino acid For example, UCU codes for serine
This unique 3 base sequence is called a CODON
A start codon is where a specific gene starts, and a stop codon is where the gene ends
A codon of DNA is transcribed into RNA 1st step of central dogma!
The Code
Once the RNA is synthesized and processed, it moves to the ribosome Remember, ribosomes are the cell organelle that make
proteinsThe ribosome reads and translates the RNA
in order to make a protein 2nd step of central dogma
Mutation
Mutations
Sometimes errors occur when chromosomes are copied
Sometimes, there is little to no effect because the cell has some repair mechanisms
Mutation: a permanent change in a cell’s DNA
Mutations
If a trait that hasn’t been present in either family suddenly appears, we can guess a mutation took place
A mutation causes a change in a child’s trait only when it takes place in the parents’ sex cells
Mutations in the autosomal cells do not get passed on
Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.
Types of Mutations
Point Mutation: chemical change in just 1 base pair Substitution: one base is exchanged for another
Missense: DNA will code for wrong amino acid Nonsense: change codon to stop codon, causes translation
to stop early
Frameshift Mutation: the gain or loss of a nucleotide Insertion: addition of a nucleotide to the DNA sequence Deletion: removal of a nucleotide to the DNA sequence
These all disrupt normal protein production and can sometimes cause genetic disorders
Causes of Mutations
Some are spontaneous
Some are caused from things outside of the cell Radiation Mutagens Various chemicals -
nicotine, pesticides
Genetic Engineering
Genetic Engineering: manipulating the DNA of one organism in order to insert the DNA of another organism Jellyfish fluorescence added
to mosquito DNAHas applications in human
health and agricultureCan be used to increase or
decrease the expression of specific traits
Biotechnology: The use of genetic engineering to solve problems
Genetic Engineering
Glow in the dark cats - researchers took skin cells from Turkish Angora female cats and used a virus to insert genetic instructions for making red fluorescent protein
Venomous cabbage - Scientists have recently taken the gene that programs poison in scorpion tails and looked for ways to combine it with cabbage
Genetic Engineering
Medicinal eggs - scientists have created a breed of genetically modified hens that produce cancer-fighting medicines in their eggs. The animals have had human genes added to their DNA so that human proteins are secreted into the whites of their eggs, along with complex medicinal proteins similar to drugs used to treat skin cancer and other diseases.
Web spinning goats - Researchers inserted a spiders’ dragline silk gene into the goats’ DNA in such a way that the goats would make the silk protein only in their milk. This “silk milk” could then be used to manufacture a web-like material called Biosteel.
Cloning
Clones: Using the DNA of one organism to create another exact copy of the organism
Plant and Animal Breeding
Cloning is a way of producing living things with identical desirable traits.
Breeding: the bringing together of two living things to produce offspring
Selective breeding: can bring out the desired traits of living things examples: dog breeding,
agricultureKnowing what to expect
tells us which living things to breed for certain traits.
Designer Babies
Using genetic engineering to choose the traits of your offspring
Savior Siblings - children conceived with the initial purpose of acting as donors for a sick brother or sister.
Gene Therapy
Technique aimed at correcting mutated genes that cause diseases
Scientists insert a normal gene into a chromosome to replace a dysfunctional gene
The Human Genome Project
The genetic blueprint for a human being
The mapping of the genome was finished in 2003, and scientists are continuing to discover what each gene does and how it functions.