DNA Deoxyribonucleic Acid DNA The genetic material Contains the blueprint for an organism Instructions for an organisms traits Nucleic Acidpolymer chain of nucleotides monomers Very long molecule ID: 911363
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Slide1
DNA and Genes
Biology: Chapter 11
Slide2DNA
Deoxyribonucleic Acid (DNA)
The genetic material
Contains the “blueprint” for an organismInstructions for an organism’s traitsNucleic Acid-polymer (chain) of nucleotides (monomers)Very long moleculeA single strand is ~3 meters longIf all uncoiled, your DNA would reach from the Earth to the Sun
Slide3DNA, Genes, and Chromosomes
DNA=hereditary material
Gene=segment of DNA that codes for a specific protein
Chromosome=tightly wound strand of DNA and proteins (histones)
Slide4Structure of Nucleotides
A nucleotide is a subunit of DNA (a monomer)
3 parts:
A Sugar (deoxyribose)A phosphate groupA nitrogenous base (Adenine (A), Thymine (T), Cytosine (C), or Guanine (G)All organisms have these same 4 basesBases come in 2 forms (based on structure)Purines: Adenine and Guanine
Pure as Gold
Pyrimidines: Cytosine, Uracil (to be discussed later) and Thymine
Py
Cut
Slide5Structure of DNA
DNA is a string of nucleotides
The structure was discovered by Rosalind Franklin using X-Ray technology
Slide6Watson and Crick
James Watson and Francis Crick (1953)
“Used”
Frankin’s work to come up with the 3-D structure of DNADNA resembles a twisted ladder or twisted zipperCalled a Double HelixNucleotides are held together by hydrogen bonds
Slide7Nucleotide Sequences
The sequence of nucleotides determines the make-up of the organism
The sequence of nucleotides on a strand of DNA is called a gene
A gene is a segment of DNA that is a code for a specific protein
Slide8DNA Replication
DNA must constantly replicate
New copy is used during cell division and production of sperm and egg (mitosis and meiosis)
Simplified ProcessAn enzyme called DNA Helicase breaks the hydrogen bonds between nucleotidesThis “unzips” the strand Another enzyme called DNA Polymerase adds a complementary nucleotide
Slide9Slide10Complementary Base Pairing
A bonds to T (apple tree)
C bonds to G (car garage)
Practice: What would be the complementary strand for the following?A T G C T GT A C G A C
Slide11RNA
Also a nucleic acid (polymer of nucleotides)
Very similar to DNA
3 parts:A sugar (ribose)A phosphate groupA nitrogenous base (Adenine (A), Cytosine (C), Guanine (G), and Uracil (U)Uracil replaces Thymine Bonds to Adenine
Slide123 types of RNA
Messenger RNA (mRNA)-Brings instructions from DNA to cytoplasm (ribosome)
Ribosomal RNA (
rRNA)-Binds to mRNA and assembles amino acids in correct order Transfer RNA (tRNA)-Carries amino acids to the ribosome
Slide13Transcription
DNA double helix unwinds
RNA nucleotides (A, U, G, C) bond to the complementary base using RNA polymerase
Forms a strand of mRNAmRNA strand breaks awaymRNA leaves the nucleus and travels to the cytoplasm, where it binds to a ribosomerRNA within the ribosome binds to the mRNA and “reads” the code
Slide14Translation
Translating mRNA into a sequence of amino acids to form a protein
Amino acids dissolved in the cytoplasm are brought to the ribosome by
tRNAtRNA contains a sequence of 3 amino acids called an anticodonThe anticodon is complementary to a codon. Example: AUG is a start codon and codes for the amino acid Methionine
Methionine will be attached to a
tRNA
molecule that has the anticodon UAC
As the amino acids attach to the mRNA strand, the
tRNA
releases and returns to the cytoplasm to pick up another amino acid
Peptide bonds are formed between the amino acids, forming a protein
Slide15Slide16Amino Acids
“The language of proteins uses an alphabet of amino acids.” (your textbook)
There are 20 common amino acids
The sequence of nucleotides determines the sequence of amino acids3 bases code for one amino acidThis group of 3 bases is called a codonExample: U U
U
= phenylalanine
Several codons may code for the same amino acid
Example UUU and UUC both code for phenylalanine
Some codons are not codes for amino acids, but instructions to start or stop transcription.
AUG=Start codon (Methionine)
UGA, UAA, and UAG=Stop codons
Slide17Slide18Protein structure
The sequence of amino acids determines the protein’s shape
Proteins of a certain sequence always form in the same 3-D shape
These proteins become enzymes and cell structures.Central Dogma of BiologyDNARNAProteins
This occurs in all organisms
It also explain how you get your traits
You get some DNA from mom, some from dad, and this DNA determines the proteins and, therefore, all of the traits you have.
Slide19When things go wrong
Mutation-Change in DNA sequence
Can be caused by many different things
Errors in DNA replication or transcriptionErrors in cell divisionExternal factors (mutagens)Radiation (sun or tanning)SmokingAlcoholAsbestos
Many more
Slide20Results of Mutations
Most mutation are bad
Can result in cell division going out of control
Leads to a mass of cells, called a tumorThis is how cancer happens.Some mutations are neutralMinor change, or the cell catches it and fixes or destroys it before In rare cases, mutations are beneficialGive the organism something it did not previously have
These are what natural selection acts on.
Slide21Point Mutations
Change in a single base pair in DNA
Alters the amino acid, and therefore the entire 3-D structure of the protein
Slide22Frameshift Mutations
Shifts the reading of codons by one base
Unlike point mutations, all amino acids after the mutation are altered, and this drastically changes the protein shape.
Slide23Chromosomal Mutations
Change to the structure of a chromosome
Part of the chromosome may break off, or fold incorrectly
Slide24Repairing DNA
Mutation sometimes occur and are able to be fixed
Certain enzymes are able to “proofread” DNA to ensure that all is well
Can replace incorrect nucleotides, or instruct the cell to destroy the DNA containing the errorsThis process is not perfect, but usually works wellBest course of action is avoiding mutagens as much as possible.