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DNA RNA Protein

Gene Expression

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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Overview of Protein

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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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DNA, Genes and Protein Synthesis

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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

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TATA box Start point

Transcriptionfactors

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Several transcriptionfactors

Additional transcriptionfactors

RNA polymerase IITranscription factors

RNA transcript

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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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• MOST gene expression control happens in TRANSCRIPTION

DNA unpacking

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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)

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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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Diseases caused by chromosome # issues

• Non disjunction

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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.