Transcript Ch. 13: Translation and Proteins

A comparison of the components in prokaryotic
and eukaryotic ribosomes.
Cloverleaf Model of
Transfer RNA
A three-dimensional
model of transfer
RNA.
TRANSLATION:
making proteins
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Steps involved in
charging tRNA.
Initiation of translation.
Elongation of the
growing polypeptide
chain during
translation
Polyribosomes as seen under the electron microscope.
Polyribosomes as seen under the electron microscope.
They were taken from giant salivary gland cells of the midgefly, Chironomus thummi.
Note that the nascent polypeptide chain is apparent as it emerges from each
ribosome. Its length increases as translation proceeds from left (5’) to right (3’) along
the mRNA.
Each amino acid has two abbreviations; that is, alanine is designated
either ala or A (a universal nomenclature).
secondary level
(a) The right-handed alpha helix, which represents one form of secondary
structure of a polypeptide chain. (b) The beta-pleated sheet, an alternative
form of secondary structure of polypeptide chains.
tertiary level
The tertiary level of protein structure in a respiratory pigment,
myoglobin. The bound oxygen atom is shown in red.
quaternary level
hemoglobin
The quaternary level of protein structure as seen in
hemoglobin. Four chains (two alpha and two beta) interact
with four heme groups to form the functional molecule.
hemoglobin
hemoglobin
sickle-cell anemia
sickle-cell anemia
sickle-cell anemia
normal hemoglobin
two sickle-cell hemoglobin molecules stuck together
sickle-cell anemia
Investigation of hemoglobin derived from HbAHbA
and HbSHbS individuals by using electrophoresis,
protein fingerprinting, and amino acid analysis.
Hemoglobin from individuals with sickle-cell anemia
(HbSHbS) (a) migrates differently in an
electrophoretic field, (b) shows an altered peptide in
fingerprint analysis, and (c) shows an altered amino
acid, valine, at the sixth position in the Beta chain.
During electrophoresis, heterozygotes (HbAHbS)
reveal both forms of hemoglobin.
sickle-cell anemia
sickle-cell anemia
Metabolic pathway involving phenylalanine and tyrosine. Various metabolic
blocks resulting from mutations lead to the disorders phenylketonuria,
alkaptonuria, albinism, and tyrosinemia.
Degradation of phenylalanine
Hydroxylation of phenylalanine to tyrosine by the
enzyme phenylalanine hydroxylase.
phenylalanine
hydroxylase
Induction, isolation, and characterization of a nutritional
auxotrophic mutation in Neurospora. (a) Most conidia are not
affected, but one conidium (shown in red) contains the mutation.
In (b) and (c), the precise nature of the mutation is established
and found to involve the biosynthesis of tyrosine.