1 DNA RNA Protein Gene Expression What is the central dogma in biology? RNA transcription RNA...
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Transcript of 1 DNA RNA Protein Gene Expression What is the central dogma in biology? RNA transcription RNA...
What is the central dogma in biology?
• RNA transcription
• RNA translation
• Pathways followed
• Differences btwn eukaryotic path and prokaryotic path
• Enzymes involved
• Modifications to pre mRNA2
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The role of the
nucleotides
• The different nucleotides spell out a code: instructions for the cell
• Each set of instructions is a gene. A gene is a long series of the letters (nucleotides) that gives instruction to the cell.
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Proteins
• Proteins are the building blocks of our bodies.
• They make up the structure of muscle, skin, brain,
• or direct the synthesis of stuff (enzymes).
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• Some proteins are enzymes that catalyze reactions– breaking down food– synthesizing neurotransmitters
• Some proteins are hormones secreted by one cell to affect distant cells– Testosterone - Estrogen
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• Proteins are made of amino acids.
• The 20 amino acids differ in their size, shape, and chemical properties.
• Think of the amino acids as 20 different letters that can be put together to make different words.
http://www.nida.nih.gov/pubs/teaching/largegifs/slide-13.gif
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• Many drugs act by replacing a protein
• Dopamine is a neurotransmitter which controls allertness and energy
Dopamine and Cocaine
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Genes and DNA
• A gene contains the code (DNA sequence) for 1 polypeptide (protein).
• Genes are located on chromosomes.
• A Codon contains code (RNA sequence) for 1 amino acid
• Codon = 3 nucleotides = code for 1 amino acid
• A typical cell expresses 20% of its genes at any given time.
• 1.5% of DNA codes for protein, less codes for rRNA and tRNA the rest is NON coding.
• Most control of gene expression happens during transcription
Gene Expression
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Basic Principles of Transcription and Translation
• Transcription is the synthesis of RNA from DNA (in nucleus)
• Transcription produces messenger RNA (mRNA)
• Translation is the synthesis of a polypeptide from mRNA (codons)
• Ribosomes are the sites of translation
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LE 17-3-5
TRANSCRIPTION
TRANSLATION
DNA
mRNA
Ribosome
Polypeptide
DNA
Pre-mRNA
Prokaryotic cell
Nuclearenvelope
mRNA
TRANSLATION
TRANSCRIPTION
RNA PROCESSING
Ribosome
Polypeptide
Eukaryotic cell
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LE 17-7
ElongationNon-templatestrand of DNA
RNApolymerase
RNA nucleotides
3 end3
5
5
Newly madeRNA
Templatestrand of DNA
Direction of transcription(“downstream”)
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Synthesis of an RNA Transcript• The three stages of transcription:
– Initiation– Elongation– Termination
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LE 17-8
Promoter
53
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TATA box Start point
Transcriptionfactors
53
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Several transcriptionfactors
Additional transcriptionfactors
RNA polymerase IITranscription factors
RNA transcript
53
355
Transcription initiation complex
Eukaryotic promoters
TemplateDNA strand
Prokaryote v. EukaryoteInitiation• Prokaryotes: RNA polymerase binds
directly to promoter
• Eukaryotes: transcription factors (group of proteins) are needed to start transcription
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Prokaryote
• RNA polymerase to promoter
• mRNA ready for use
Eukaryote
• Transcription factors needed for bind to promoter
• mRNA needs modifications to exit nucleus
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Eukaryote modify mRNA
5’ end cap (guanine)
3’ end Poly A tail (adenine)
• Purpose: – facilitate move mRNA out of nucleus– Facilitate bind to ribosome
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Translation
• mRNA Nucleotides are grouped into codons.
• Each codon contains three nucleotides.
• Each codon corresponds to a specific amino acid or a stop.
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LE 17-4
DNAmolecule
Gene 1
Gene 2
Gene 3
DNA strand(template)
3
TRANSCRIPTION
Codon
mRNA
TRANSLATION
Protein
Amino acid
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5
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tRNA and Ribosomes
• Transfer RNA (tRNA) translates the codons to amino acids.
• This takes place on a ribosome, which facilitates the building of the poly-peptide chain.
• DNA is transcribed to produce RNA• RNA is translated to produce protein
• DNA -> -> protein
• DNA is stable and long-lived• RNA is quickly degraded in the cell
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P Site A Site
E Site
Amino Acids forming Peptide chain
Ribosome
tRNA
anti-codon
codon
Translation
UAC
AUG
Tyr
GUA
CAU
Val
mRNA strand
3’
5’
HisMet Pro
GGA
CCU
Codons: initiate & stop
• Stop codons: UAA, UAG, UGA
• Start codon: AUG – is the codon for initiation of protein
synthesis in all organisms– Methionine
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Gene expression
• Humans have 30,000 or more genes.
• Many genes encode proteins that perform functions only on a particular tissue, such as in brain, in kidney, or in muscle.
• Most genes are not turned on (expressed) in most tissues.
• A gene must be expressed before it produces the corresponding protein.
Point mutations
• Point mutation: changes in ONE base pair of a gene– Insertions– Deletions– Additions
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Sickle Cell
• Sickle cell: change in single base pair in the beta-hemoglobin gene that codes for one of the polypeptides in hemoglobin
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Substitution point mutations
• Usually not a huge problem.
• Might code for SAME amino acid
• Might code for “different” amino acid with similar characteristics.
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Insertions or deletions
• Addition or subtraction of base pair
• DISASTEROUS effects: because, cause frameshift mutation:
• All of the base pairs “downstream” from the mutation will be wrongly grouped into codon!!
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Diseases caused by Point Mutation
• Cystic Fibrosis: – Mutation in gene involved in movement of water and stuff in and out of
cell
– This causes the build up of thick, sticky mucus
• Sickle Cell Anemia
• Colorblind:– Genetic disease- (X-link): loss of cones in retina
• Tay Sachs disease:• Genetic Disease – inherited- caused by mutation in gene to break
down fatty substance…. Get lethal accumulation of fatty subst. in brain and spinal cord
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Common Chromosomal Abnormalities
http://anthro.palomar.edu/abnormal/abnormal_4.htm
• Two Main Categories– Structural modification– Irregular number
• Typically result from nondisjunction during meiosis
• Polyploidy-complete multiples of sets of chromosomes (23+23+23)
• Aneulploidy-addition or loss of chromosomes within a set (23+22)
Autosomal Defects
http://anthro.palomar.edu/abnormal/abnormal_4.htm
Down’s Syndrome• Typically trisomy of
chromosome 21• Some have
translocation of 21 to 14 or 15
• 2-4% are genetically mosaic
• 75-80% of Down syndrome children are born to women under 35
Monosomy• Only one set of
chromosomes remains after fertilization
• All fetuses will spontaneously abort
Female AbnormalitiesFemale Abnormalities Male AbnormalitiesMale Abnormalities
http://anthro.palomar.edu/abnormal/abnormal_4.htm
• Metafemale(XXX)– Unusually tall, low to
normal intelligence– Normal sex characteristics,
fertile
• Turner Syndrome (XO)– Ovaries do not develop,
and do not ovulate– Lack secondary sex
characteristics– Slight mental retardation
• Klinefelter Syndrome (XXY)– High-pitched voice– Asexual to feminine body
type– Low testosterone, sterile– 1 in 500
• XYY Syndrome– Unusually tall, severe acne– High testosterone levels,
possibly leading to violence
Sex Chromosome Abnormalities
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Measuring gene expression
• Quantitative PCR (Polymerase Chain Reaction): – A method to isolate and measure the DNA expression
level of a gene.
– This technique can be used to identify with a very high-probability, disease-causing viruses and/or bacteria, a deceased person, or a criminal suspect.Microarrahttp://people.ku.edu/~jbrown/pcr.htmlys:
http://www.walkerbioscience.com/powerpoint/bio45/bio45-1/Brain%20course%20intro.ppt#10
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Other ways of visualizing DNA
DNA can be run on an agarose gel, which separates DNA pieces based on size. A charge is applied, and because DNA is slightly negatively charged, it will run through the gel towards the positive charge.
Larger pieces of DNA
Smaller pieces of DNA
+
-Smaller pieces of DNA can more easily move through the gel and will end up closer to the bottom.