DNA and Genes Biology: Chapter 11 - PowerPoint Presentation

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DNA and Genes

Biology: Chapter 11

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DNA

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

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DNA, 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)

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Structure 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

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Structure of DNA

DNA is a string of nucleotides

The structure was discovered by Rosalind Franklin using X-Ray technology

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Watson 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

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Nucleotide 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

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DNA 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

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Complementary 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

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RNA

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

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3 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

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Transcription

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

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Translation

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

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Amino 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

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Protein 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 BiologyDNARNAProteins

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.

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When 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

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Results 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.

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Point Mutations

Change in a single base pair in DNA

Alters the amino acid, and therefore the entire 3-D structure of the protein

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Frameshift 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.

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Chromosomal Mutations

Change to the structure of a chromosome

Part of the chromosome may break off, or fold incorrectly

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Repairing 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.