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DNA. C. G. T. A. Hydrogen bond. T. A. Base pair. T. A. G. C. G. C. G. C. A. T. C. G. C. G. T. A. A. T. A. T. T. A. T. A. G. C. A. T. Computer model. Ribbon model. Partial chemical structure. Animation: Campbell Ch 10 – DNA Double Helix. - PowerPoint PPT Presentation
Citation preview
Hydrogen bond
Basepair
Ribbon model Partial chemical structure Computer model
G C
T A
A T
TA
C
C
G
G
GC
T
T
T
T
A
A
A
A
G C
A T
A
C
T
G
CG
AT
DNA
What does the cell use DNA for?
• Gives you traits
What IS a trait?
• Physical structure produced by a protein!• DNA controls the production of proteins.
What do we know about making proteins?
DNA is in the NUCLEUS
RIBOSOMES, ER, and GOLGI are in the CYTOPLASM
How does that work?
• RNA acts as a messenger to carry information from the DNA in the nucleus to the ribosomes in the cytoplasm
What’s RNA?
• Nucleic Acid• Similar to DNA• Some differences
Phosphategroup
Nitrogenous base(A, G, C, or U)
Sugar(ribose)
Uracil (U)
What’s RNA?
FEATURE DNA RNA
Subunits Nucleotide Nucleotide
Strands 2 – double helix 1 (mostly)
Sugar Deoxyribose Ribose
Bases A = T; C = G A = U; C = G
Protein Synthesis Overview
DNA is located in the NUCLEUS
Protein Synthesis Overview
A messenger RNA (mRNA) copy is made of DNA.
Protein Synthesis Overview
mRNA leaves the nucleus and goes to the ribosome
Protein Synthesis Overview
Ribosome uses mRNA to assemble amino acids in the correct order to make a specific protein
Genes to Polypeptides
• Polypeptides = chains of AA = proteins
• 20 different AA exist• specific polypeptide has
specific AA sequence• Sequence of AA
determines the shape and function of a protein
Genes to Polypeptides
• Sequence of bases in DNA determine AA sequence
• “Genes” store order of AA in a code in DNA
• One specific gene will yield one* specific polypeptide – polypeptide = protein
that does a job!
DNA & Genetic Code
• There are 20 amino acids, and a stop
• How can DNA specify 21 things with only four bases?
Genetic Code
• IF: 1 base = 1 amino acid
• THEN: how many amino acid possibilities are there?
GATC
4
Genetic Code
• IF: 2 bases = 1 amino acid
• THEN: how many amino acid possibilities are there?
GATC
4 x 4 = 16
GATC
Genetic Code
• IF: 3 bases = 1 amino acid
• THEN: how many amino acid possibilities are there?
GATC
4 x 4 x 4 = 64
GATC
GATC
DNA & Genetic Code
• In a gene, every three bases code for a specific amino acid (one of the 20)
• 4 x 4 x 4 = 64 total possiblities
• One amino acid can be coded for by more than one triplet
DNA & Genetic CodeGenetic code is composed of codons made up of of base triplets
DNA & Genetic Code
• The genetic code is both universal and degenerate. – Universal = found in all living organisms– Degenerate = having more than one base triplet
(codon) to code for one amino acid
Protein Synthesis Overview
• DNA is located in the nucleus
Protein Synthesis Overview
• Ribosomes are located in the cytoplasm
Protein Synthesis Overview
• Messenger RNA carries “message” from DNA to ribosomes
Transcription
• Genes are made of DNA• DNA cannot leave the
nucleus• A copy must be
“transcribed” into RNA• RNA exits nucleus
http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm
Transcription
1. INITIATION: RNA polymerase uncoils DNA double helix
2. ELONGATION: RNA polymerase creates a new mRNA strand using free RNA nucleotides; a single DNA template strand is used
Transcription
3. RNA nucleotides attached together (type of reaction?) via RNA polymerase
4. TERMINATION: New mRNA strands separates from DNA
5. DNA reforms
Animation: Campbell Ch 10 – 10_9 TranscriptionAnimation: Campbell Ch 10 – 10_9 Transcription
GENE Contains the instructions to assemble one protein
TRANSCRIPTION The process by which an mRNA copy is made of a DNA sequence
RNA POLYMERASE Enzyme that catalyzes synthesis of mRNA strand
PROMOTER REGION Sequence of DNA bases within gene where RNA polymerase binds
CODING REGION Sequence of DNA bases that codes for the actual structure of the protein
TERMINATOR REGION
Sequence of DNA were RNA polymerase stops transcribing.
CODON 3 bases of DNA or RNA; specifies 1 amino acid
What’s it look like?
So, the new mRNA strand was just made, now what?
Final Steps – Eukaryotes ONLY
1. mRNA Splicing – INTRONS: non-coding
regions of the mRNA strand
– EXONS: coding regions of the mRNA strand
– Introns are spliced out of final mRNA
Final Steps – Eukaryotes ONLY
2. 5’ Cap– Modification to 5’ end
of mRNA– Ensures stability of
mRNA
Final Steps – Eukaryotes ONLY3. 3’ poly-A tail
– Addition of poly-A to 3’ end of mRNA– Protects RNA from nucleases
ExonExon ExonIntronIntron
Cap
DNA
RNAtranscriptwith cap and tail
mRNA
Coding sequenceNucleus
Cytoplasm
Exons spliced together
TailIntrons removed
TranscriptionAddition of cap and tail
Animation: Cain Ch13a03 - TranscriptionAnimation: Cain Ch13a03 - Transcription
Transcription in a cell
• Multiple genes can be transcribed at the same time
• The same gene can be transcribed at the same time
Translation
DNA mRNA ProteinTranscription Translation
Where we are now.
Nucleus Ribosome (cytoplasm)
Translation Summary
• Instructions in the mRNA are used by a ribosome to assemble amino acids in the correct order
• Order of amino acids gives the protein its shape
• Shape gives protein its function
Translation Summary
The Key Players• mRNA• tRNA• rRNA
The Stages of Translation• Initiation• Elongation• termination
Animation: Cain Ch13a07 - TranslationAnimation: Cain Ch13a07 - Translation
mRNA (messenger RNA)
• copy of the directions to make the product (protein)
• tells the ribosome the correct sequence of Amino Acids while putting together the protein
• each codon (3 bases) directs a specific amino acid to be added to the growing protein
tRNA (transfer RNA)
• the delivery RNA; delivers specific Amino Acids to the ribosome
• composed of RNA• anticodon binds to a
corresponding codon on mRNA
• Carries one specific amino
Translation6.4.1
rRNA (ribosomal RNA)
• ribosomes are made of RNA and protein
• composed of two subunits: the 30s and 50s subunits
• two tRNA binding sites; one mRNA binding site
Translation INITIATION
• small (30S) ribosome subunit binds to mRNA at the 5’ end of the mRNA
• 30S moves along mRNA 5’ to 3’ until it hits the start codon AUG
Translation INITIATION
• large subunit binds• Methionine tRNA moves into ribosome
Translation INITIATION
• another tRNA, with the anticodon complementary to the next codon binds to the ribosome
Translation ELONGATION
• first amino acid added• ribosome moves down
mRNA to next codon• next tRNA comes in• its amino acid is bound
to the polypeptide chain
• ribosome moves down mRNA to next codon
Translation TERMINATION
• the ribosome encounters a stop codon• no tRNA molecule has an anticodon for this
codon
Translation TERMINATION
• polypeptide is released and ribosome disassociates
Animation: Campbell Ch 10 – 10_14 TranslationAnimation: Campbell Ch 10 – 10_14 Translation
Where does translation happen?
• Cytoplasmic (free) Ribosomes proteins for use in cytoplasm
• Rough ER (attached) Ribosomes proteins secreted or used in lysosomes
• DNA– TRANSCRIPTION
• RNA– TRANSLATION
• PROTEIN
DNA molecule
Gene 1
Gene 2
Gene 3
AAAAA C C GG C
CCGG G U U U UUUU
AADNA strand
Transcription
RNA
Translation
Polypeptide
Amino acid
Codon
Interpreting the Genetic CodeSecond base
Firs
t bas
e
Thir
d ba
se
UUUU C A G
GAA
C
U
U
U
C
AC
A
G
G
UCAG
U
C
A
G
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
Leu
lle
AUG Met orstart
GUU
GUC
GUA
GUG
Val Ala
Thr
GCG
GCA
GCC
GCU
ACG
ACA
ACC
ACU
Pro
CCG
CCA
CCC
CCU
UCG
UCA
UCC
UCU
Ser
Tyr CysUAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
His
Gln
Stop
Stop
UGU
UGC
UGA
UGG Trp
Stop
Arg
CGU
CGU
CGA
CGG
Asn
Lys
Asp
Glu
Gly
Arg
SerAAU AGU
AAC
AAA
AAG
GAU
GAG
AGC
AGA
AGG
GGU
GGC
GGG
Phe
Leu
GAC
GAA
GAG
GGA
Strand to be transcribed
Transcription
DNAT
A GT
A C T T
T T
A A
AA G
C
G
C
T T
TA A
A
A GURNA
Translation
Startcodon
A A U UG U U A G
Stopcodon
PheLysMetPolypeptideAnimation: Starr Ch 14 – Genetic codeAnimation: Starr Ch 14 – Genetic code
Changes in the Genetic Code
• MUTATION = change in the nucleotide sequence of DNA
Normal hemoglobin DNA
mRNA
C T T
AAG
Normal hemoglobin
Glu
mRNA
C
G
A
Sickle-cell hemoglobin
Val
Mutant hemoglobin DNA
A
T
U
Changes in the Genetic Code
• MUTATION = change in the nucleotide sequence of DNA
Normal hemoglobin DNA
mRNA
C T T
AAG
Normal hemoglobin
Glu
mRNA
C
G
A
Sickle-cell hemoglobin
Val
Mutant hemoglobin DNA
A
T
U
Changes in the Genetic Code
• MUTATION = change in the nucleotide sequence of DNA
Normal hemoglobin DNA
mRNA
C T T
AAG
Normal hemoglobin
Glu
mRNA
C
G
A
Sickle-cell hemoglobin
Val
Mutant hemoglobin DNA
A
T
U
What causes mutations?
• Spontaneous mutations: uncorrected errors in replication
What causes mutations?
• Spontaneous mutations: uncorrected errors in replication
• Harmful environmental agents: UV light, radiation, chemicals
Radiation damages DNA
Radiation as a cancer treatment
Why would radiation be a treatment for cancer?
• What type of cells would radiation affect most: rapidly dividing or rarely dividing cells?
• Cancer cells are very rapidly dividing cells
• Radiation targets ALL rapidly dividing cells, not just cancer cells
What causes mutations?
• Spontaneous mutations: uncorrected errors in replication
• Harmful environmental agents: UV light, radiation, chemicals
• Transposable elements: “jumping genes”
Mutations
• Sickle Cell Anemia– Single-base substitution
Sickle Cell Anemia
Missense mutation = single base substitution
Changes one amino acid
Variable effect on protein depending on how much structure is changed
Missense Mutations
• Tay Sachs Disease– Single-base substitution
in HexA gene
Missense Mutations
• Cystic Fibrosis– Single-base substitution
in CFTR gene
Nonsense mutation = single base substitution that introduces a STOP
Truncates proteinOften more severe
Nonsense Mutations
• Cystic Fibrosis– More severe form
• Duchenne Muscular Dystrophy– Dystrophin – connects
cytoskeleton to extracellular matrix
Silent mutation = single base substitution that doesn’t change an
amino acidSecond base
Firs
t bas
e
Thir
d ba
se
UUUU C A G
GAA
C
U
U
U
C
AC
A
G
G
UCAG
U
C
A
G
UUC
UUA
UUG
CUU
CUC
CUA
CUG
AUU
AUC
AUA
Leu
lle
AUG Met orstart
GUU
GUC
GUA
GUG
Val Ala
Thr
GCG
GCA
GCC
GCU
ACG
ACA
ACC
ACU
Pro
CCG
CCA
CCC
CCU
UCG
UCA
UCC
UCU
Ser
Tyr CysUAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
His
Gln
Stop
Stop
UGU
UGC
UGA
UGG Trp
Stop
Arg
CGU
CGU
CGA
CGG
Asn
Lys
Asp
Glu
Gly
Arg
SerAAU AGU
AAC
AAA
AAG
GAU
GAG
AGC
AGA
AGG
GGU
GGC
GGG
Phe
Leu
GAC
GAA
GAG
GGA
Insertion mutation = addition of one or more nucleotides
Can change entire protein after mutation
Deletion mutation = deletion of one or more nucleotides
Can change entire protein after mutation
Frameshift mutation = Change of “reading frame” in DNA
Can change entire protein after mutation
Insertion or deletion
Cancer
• BRCA1 - increased risk of developing breast cancer
• Mutations due to mutagens
Summary of Mutations
• Base Substitution– Missense– Nonsense– Silent
• Frameshift– Insertion– Deletion
• Which kind would be most likely to cause disease?
Normal gene
Base substitution
ProteinmRNA
Base deletion Missing
Met
Met
Met Lys
Lys
Lys Phe Gly Ala
AlaPhe
Ala
Ser
Leu His
A
A A A A
A A A
A
AAAAA U U U U
UUUU
U U U U G G GGG
G G G G
C C
C C
G G G G G CC
U
Good information about genes and mutations
• http://ghr.nlm.nih.gov/handbook/basics
Effect of Mutation on Protein Structure
Effect of Mutation on Protein Structure
Transcription Assembly of RNA on unwound regions of DNA molecule
mRNA rRNA tRNAmRNA processing
mature mRNA transcripts ribosomal
subunitsmature tRNA
Convergence of RNAsTranslation cytoplasmic
pools of amino acids,
ribosomal subunits, and
tRNAsAt an intact ribosome, synthesis of a polypeptide chain at the binding sites for mRNA and tRNAs
Protein
Animation: Starr Ch 14 - Protein Synthesis in Prokaryotes vs Eukaryotes
Animation: Starr Ch 14 - Protein Synthesis in Prokaryotes vs Eukaryotes
In-class assignment – Protein Synthesis
• Complete the classwork assignment
Gene Expression
• Every cell in your body came from 1 original egg and sperm
• Every cell has the same DNA and the same genes
76
Gene Expression
• Every cell in your body came from 1 original egg and sperm
• Every cell has the same DNA and the same genes
• Each cell is different, specialized• Differences due to gene expression
– Which genes are turned on– When the genes are turned on– How much product they make
77
Genetic Potential
• Embryonic Stem Cells– Can differentiate to
become any type of cell in the body
• Adult Stem Cells– Can differentiate to
become several types of cell
Root ofcarrot plant
Root cells culturedin nutrient medium
Cell divisionin culture Plantlet Adult plant
Single cell
Genetic Potential
• Plants in Cell Culture• Plants creating roots
Genome Size
• Genome: total amount of DNA
• Prokaryotes– 0.6 to 30 million base pairs– Approximately 2,000 genes
• Eukaryotes– 12 million to 1 trillion base
pairs– Humans have ~25,000
genes
80
Organization of DNA
• Prokaryotes– Several million base pairs -
one circular piece– Related genes grouped
together– Mostly coding DNA
81
Organization of DNA
• Eukaryotes– Billions of base pairs –
several linear chromosomes
– Genes not grouped– Mostly non-coding DNA
82
83
Noncoding DNA
• Spacer DNA• Transposons – “selfish DNA”
84
DNA Packaging
• Eukaryotic chromosomes are very large• Must be packaged to fit inside nucleus• Unavailable for transcription• Unpacking must occur before transcription
85
Levels of Packaging
• Chromosome – fully condensed
• Tightly packed loops• 30 nm fibers• Histone spool• Double helix
86
Patterns of Gene Expression
• Bacteria directly exposed to environment• Respond to changes in nutrient availability
directly– Make enzymes for nutrients when they are
present– Turn genes off when they are not
87
Patterns of Gene Expression
• Eukaryotic cells• Tissue specific expression• Housekeeping
genes
Gene Expression: Development
• Embryo development depends on gene expression
• Timing of expression vital
• Controlled by cascades of gene expression
88
89
Levels of Gene Control
1. Packaging2. Transcription3. mRNA maturation4. mRNA breakdown5. Translation 6. Protein Regulation 7. Protein Degradation
1. Packaging
• If the DNA isn’t unwrapped from the histones, it can’t be transcribed
• DNA Methylation• HistoneMethylation
Animation: Campbell Ch 11 – DNA PackingAnimation: Campbell Ch 11 – DNA Packing
1. Packaging
Methylation
• DNA marked with a methyl group can be identified by an enzyme
1. Packaging
• X chromosome Inactivation– Females have 2 X
chromosomes– One gets methylated
and inactivated during development
1. Packaging
• “Copycat” – first cloned cat
1. Packaging
• Agouti, mottled and yellow mice
1. Packaging
• Methylation is required for development– Lethal to eliminate methylation in animals– Not lethal in plants, but profound effects on
development
1. Packaging
• Imprinting – methylate and silence genes on one parent’s chromosome specifically– About 1% of total human genes (about 300 genes)
1. Packaging
• Parental DNA contributions to embryo are marked
1. Packaging
• Normal = maternal expressed, paternal silenced
• Prader-Willi = paternal allele lost, maternal allele present
• Angelman = maternal allele lost, paternal allele present
1. Packaging
• Cancer cells are often aberrantly methylated
1. Packaging
• Cancer cells are often aberrantly methylated
2. Transcription
• Control when and how much a gene is transcribed
2. Example of Transcriptional Control: The Lac Operon in Bacteria
• E. coli lactose sugar utilization genes
• When lactose is present, bacteria needs to have the proteins coded for by these genes– Lactase Enzymes
Lac Operon Animation (online)Lac Operon Animation (online)
2. Example of Transcriptional Control: The Lac Operon in Bacteria
• Operon: group of nucleotide sequences including an operator, a promoter, and one or more genes that are controlled as a unit to produce messenger RNA (mRNA)
*The Operon model is one example of gene expression regulation
Lac Repressor Protein
• NO LACTOSE: repressor binds to the DNA and prevents RNA pol from binding (no transcription)
• No lactase is produced
6.3.2
Lac Repressor Protein
• LACTOSE: repressor binds lactose and changes shape. Now repressor can’t bind DNA
• Lactase is produced; lactose is metabolized
6.3.2
107
2. Example of Transcriptional Control: The Trp Operon
Tryptophan AA genes
ANIMATION (Ch14a03)
2. Transcriptional Control - Eukaryotic Gene Expression
• No operons• More complex than prokaryotic• Many different types of regulatory proteins• Many DNA elements controlling each gene
108
2. Transcriptional Control - Eukaryotic Gene Expression
• OFF: proteins are produced that bind to gene preventing RNA polymerase from binding
3. mRNA Maturation
• If 3’ cap, 5’ poly-A tail are not added, mRNA cannot be transported out of the nucleus and used
• mRNA can be “alternatively spliced” to generate different transcripts
Exons
orRNA splicing
mRNA
RNAtranscript
DNA
4. mRNA Breakdown
• If mRNA is broken down more quickly, it can be used fewer times
5. Translational Regulation
• Inhibit any of the steps of translation and the mRNA can’t be used
6. Protein Regulation
• Activate or inactivate the newly made protein– Phosphorylation– Acetylation
6. Protein Regulation
• Activate or inactivate the newly made protein– Phosphorylation– Acetylation– Cleavage
INSULIN
7. Protein Degradation
• If the protein is broken down, obviously it can’t work anymore