DNA: Molecule of Life
Transcript of DNA: Molecule of Life
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DNA: Molecule of LifeHistory
DNA Structure
Protein Synthesis
Gene Regulation
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History of DNA• By the 1940’s, scientists knew that
chromosomes consisted of both DNA and protein but did not know which was the genetic material.
• Scientists wanted it to be protein since they knew more about its structure.
• The following experiments shed some light.
HISTORY
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Disease-causing bacteria (smooth
colonies)
Harmless bacteria (rough colonies)
Heat-killed, disease-causing bacteria (smooth colonies)
Control(no growth)
Heat-killed, disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Dies of pneumonia Lives LivesLive, disease-causing
bacteria (smooth colonies)
Dies of pneumonia
Harmless, live R strain somehow became disease causing S strain – transformation HOW?
Animation here
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Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium No radioactivity inside
bacterium
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Hershey Chase Experiment
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DDNNAA
SSTTRRUUCCTTUURREE
Hydrogen bonds- very weak
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Nucleotide: the monomer (repeating unit) of DNA
Phosphate group
Nitrogen bases
Deoxyribosesugar
What limitations exist in our model of DNA?
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Chromosome
Supercoils
Coils
Nucleosome
Histones
DNA
double
helix
•• Chromatin:Chromatin: DNA unassociated with structural proteins.
•• ChromosomeChromosome is made up of a DNADNA-HistoneHistoneproteinprotein complex.
• Compacts a very long (2m) sequence of DNA.
DDNNAA
SSTTRRUUCCTTUURREE
DNA packing (ExpLIFE 12.1)
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DDNNAA
RREEPPLLIICCAATTIIOONN
DNA Replication Animation
Helicase unwind and separate the double helix, breaking weak H-bonds: replicationfork
DNA polymerasesrebuild each strand adding nucleotides to each side according to base-pairing rules.
Each new double helix consists of one old strand linked to one new DNA strand.
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DNA
REPLICATION
• Errors sometimes occur (about 1 error/10,000 pairs)• If a mismatch occurs, the DNA polymerase can
backtrack, remove the incorrect nucleotide, and replace it with the correct one.
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• Eukaryotic chromosomes are so long that it would take 33 days to replicate a typical human chromosome if there were only one origin of replication.
• Human chromosomes are replicated in about 100 sections that are 100,000 nucleotides long, each section with its own starting point.
• Because eukaryotic cells have multiple replication forks working at the same time, an entire human chromosome can be replicated in about 8 hours.
Prokaryotic vs. Eukaryotic
What observations can you make between the Pro/Eukaryotic DNA?
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• What are the critical characteristics of DNA that allow both the lasting storage of information and the transfer of information through copying (replication)?
• What are the dis/advanages of an information transfer system that uses as physical pattern, or template?
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How does the DNA store and transmit these messages?
A particular sequence (a gene) along a strand of DNA codes for the production of a specific protein. In this activity, you will explore the production of one protein produced by your stomach. This protein, pepsinogen, is an inactive form of an enzyme that aids in digestion.
Exp Life CD: 11.4
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Ribonucleic Acid (RNA)
UracilThymine
RiboseDeoxyribose
Single StrandDouble Strand
Click to play the video.
RNARNADNADNA
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Gene Transcription and Translation
Prokaryotes vs. Eukaryotes Gene processing animation
RNA processing
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DNA
RNA
DNA unwinds
DNA template TAC AAG TTT GAC CATTAC AAG TTT GAC CATNon-template ATG TTC AAA CTG GTAATG TTC AAA CTG GTA
Click to play the video.
Transcription: DNA ���� RNA
UUC AAA CUG GUAUUC AAA CUG GUARNA strand AUGAUG
RNA polymerase copies at a rate of 60 nucleotides/sec
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mRNAmRNA
RNADNA
RNApolymerase
Start codon
RibosomeRibosome
Methionine
Phenylalanine tRNAtRNALysine
Nucleus
mRNAmRNA
Translation observation (BSCS DVD 3 )
Translation details
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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA exits, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.
mRNARibosome
Translation direction
LysinetRNA
tRNA
Ribosome
Growing polypeptide chain
mRNA
Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop stop codonscodons . The result is a growing polypeptide chain.
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Start codon
Codons in mRNA
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Mutation - changes in DNA
• Substitution codon 2 as GTA
• Substitution codon 2 as GCG
• Insertion codon 1 TATC
• Deletion nucleotide
DNA template TAC GCA TGG AAT ACTATG CGT ACC TTA TGA
RNA transcript AUG CGU ACC UUA UGAAmino acids Met– Arg– Thr– Leu stop
Point Mutation
Frame Shift Mutation
1 2 3 4 5
Silent Mutation
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• Transcribe and translate the two DNA sequences.
• What kind of mutation does this represent?
• Explain why the correct sequence is important to protein synthesis.
• Assume the base sequence is GGG CTT CTT AAAWould this result in sickled hemoglobin? Explain.
Normal hemoglobin GGG CTT CTT TTT
Sickled hemoglobin GGG CAT CTT TTT
As a result of this mutation, the proteins are also misshapen causing sickled cells to clog capillaries and prevent normal flow of blood to body tissues, causing severe pain.
Protein structure
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Deletion
Duplication
Inversion
Translocation
Chromosomal Mutations (ExpLIFE 12.2)
How can the movement of genes take place?
Which mutation variety would be most damaging?
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Regulation of Protein Synthesis• Every cell in your body, with the exception of
gametes, or sex cells, contains a complete copy of your DNA. Why, then, are some cells nerve cells with dendrites and axons, while others are red blood cells that have lost their nuclei and are packed with hemoglobin? Why are cells so different in structure and function? If the characteristics of a cell depend upon the proteins that are synthesized, what does this tell you about protein synthesis?
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Regulatory sites
Promoter(RNA polymerase binding site)
Start transcription
DNA strand
Stop transcription
Typical Gene Structure
• lac operon (ExamView)
• Exploring a stretch of code of DNA
•Chromosome 11 Fly-over
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Complexities of Gene Expression• The relationship between genes and their effects is
complex. Despite the neatness of the genetic code, every gene cannot be simply linked to a single outcome.
• Some genes are expressed only at certain times or under specific conditions.
• Variations and mistakes can occur at each of the steps in replication and expression.
• The final outcome of gene expression is affected by the environment of the cells, the presence of other cells, and the timing of gene expression.
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Section 12-5
1. Do you think that cells produce all the proteins for which the DNA (genes) code? Why or why not? How do the proteins made affect the type and function of cells?
2. Consider what you now know about genes and protein synthesis. What might be some ways that a cell has control over the proteins it produces?
3. What type(s) of organic compounds are most likely the ones that help to regulate protein synthesis? Justify your answer.