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Chapter 14


Biological Sciences
Course Code
Clare Hasenkampf

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[14] Gene Structure & Expression
- Application to Genetics: Creating copies of mussel genes to create mussel
proteins that imitate that of mussel structure of Mytilus. Used as material
to firmly hold body parts together
- One Universal Truth of Life: Every protein is put together on ribosomes
following the instructions transcribed from genes coded w/in DNA
- organelle for protein syn. = ribosomes
- As we read, note these distinctions:
> kinds of info coded in DNA
> prokar. vs eukar. mchsms
> stucture of genes coding for proteins vs structure of genes coding for
14.1 Connection b/ween DNA, RNA and Protein
- How discovery was made that DNA codes info to create proteins
14.1a Genes Specify Either Protein or RNA Products
[1] - Garrod's r'srch on patients w/ alkaptonuria (blk urine)
-- concluded "inborn (natural) error of metabolism" caused disease
-- those having alkaptonuria unable to metabolize particular chem.
that ends up being released in their urine.
-- r'srch showed link b/ween genes & metabolism
- cause: defect in fcn of enzyme to break down chem. b/c of altered
gene, thereby displaying phenotype (blk urine) of disease.
[2] Beadle and Tatum Experiment on Neurospora crassa
- worked w/ fungi capable of syn.zing all its needed nutrients & molec's
given minimal medium

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- takes simple chem's and builds nearly all biomolec's crucial for its growth
and reprod.
(ex. building blocks for RNA, proteins, DNA)
The Experiment:
- subjected Neurospora to X-rays (mutation-inducing agent)
- found that certain exposed members no longer able to survive in minimal
medium environ w/out giving additional nutrient supply
= \ auxotrophs - term to describe mutant strains not able to grow on MM
(aka nutritional mutants)
- hypothesized that auxotrophs had gene defects that prevented them from
syn. enzymes for making req. nutrients, thus have to rely on added supply.
- linked what gene defect targetted WITH what nutrient the strain req. in
additional supply.
(ex. req. Arg amino acid means that enzyme component in multi-step
process to syn. Arg is defective)
= arg mutants)
- Arg mutant analysis
- found that biochemical pathway exclusive to syn. Arginine, critical
nutrient req. for strains to survive

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= one gene-one enzyme hypothesis : relationship that says that gene
encodes specific enzyme.
Revision Req. for One Gene-One Enzyme Hypothesis
- protein syn. not exclusive to enzymes, but wide range of proteins
- majority of proteins:
-- not enzymes
-- comprise of one/multiple polypep structure.
-- change to: One Gene-One Polypeptide hypothesis
-- polypep = molec created following coding instructions from gene.
14.1b The Pathway from Gene to Polypeptide Involves Transcription
& Translation
[1] TRANSCRIPTION (aka scrip())) - mchsm thro which info coded w/in
DNA used to make complementary RNA version of it.
- info from one nucleic acid (DNA molec) passed on to other nucleic
acid (RNA molec)
Transcription [In-depth]
- RNA polymerase makes RNA seq. (= mRNA ~ messenger RNA) being
complementary to DNA seq. of the gene of desire
- Complementary base pairing rules apply ((A) w/ (T), (G) w/ (C))
- RNA polymerase reads one of the DNA strands as temp. strand
[2] TRANSLATION (aka slati()) - mchsm thro. which info coded w/in RNA
used to put together amino acids to form polypep's
- info. converted from one molec (RNA) into diff. molec type (amino
Translation [In-depth]
- mRNA joins up w/ ribosome
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