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Proteinas

estructura primariaestructura secundaria

estructura terciaria

estructura cuaternaria

Molculas envueltas en traduccin

tRNArRNA

mRNA

proteinas

Proceso de traduccin

formacin de la estructura primaria- unin de los amino cidos por enlacespeptidicos

cual de las molculas envueltas cataliza la formacin del enlace peptidico?

Genotipo-fenotipo/genes- funcin de las proteinas

Traduccin

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mRNA procariota y eucariota

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Flujo de informacin gentica eucariota

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Polypeptide synthesis has a directionality that

parallels the 5 to 3 orientation of mRNA

During each cycle of elongation, a peptide bond isformed between the last amino acid in the

polypeptide chain and the amino acid being added

The first amino acid has an exposed amino group

Said to be N-terminal or amino terminal end

The last amino acid has an exposed carboxyl group

Said to be C-terminal or carboxy terminal end

Refer to Figure 13.5

A Polypeptide Chain Has

Directionality

13-29

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13-30Figure 13.5

Carboxyl

group

Amino

group

Condensation

reactionreleasing a water

molecule

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13-31Figure 13.5

N terminal C terminal

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13-32Figure 13.6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display

There are 20 amino acids that may be found in polypeptides

Each contains a different side chain, orR group

Nonpolar amino acids arehydrophobic They are often buried

within the interior of afolded protein

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13-33Figure 13.6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Nonpolar and charged amino acids are hydrophilic

They are more likely to be on the surface of the protein

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There are four levels of structures in proteins

1. Primary

2. Secondary

3. Tertiary 4. Quaternary

A proteins primary structure is its amino acid

sequence

Refer to Figure 13.7

Levels of Structures in Proteins

13-34

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13-35Figure 13.7

The amino

acid

sequence of

th

e enzymelysozyme

129 amino

acids long

Within the cell, theprotein will not befound in this linearstate Rather, it will adapt

a compact 3-Dstructure

Indeed, this foldingcan begin duringtranslation

The progression from

the primary to the 3-Dstructure is dictated bythe amino acidsequence within thepolypeptide

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The primary structure of a protein folds to form

regular, repeating shapes known as secondary

structures

There are two types of secondary structures E helix

F sheet

Certain amino acids are good candidates for each structure

These are stabilized by the formation of hydrogen bonds

Refer to Figure 13.8

Levels of Structures in Proteins

13-36

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The short regions of secondary structure in a proteinfold into a three-dimensional tertiary structure

Refer to Figure 13.8

This is the final conformation of proteins that are

composed of a single polypeptide Structure determined by hydrophobic and ionic interactions as well as

hydrogen bonds and Van der Waals interactions

Proteins made up of two or more polypeptides have

a quaternary structure

This is formed when the various polypeptides associate

together to make a functional protein

Refer to Figure 13.8

Levels of Structures in Proteins

13-37

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13-38Figure 13.8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display

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To a great extent, the characteristics of a cell depend on the

types of proteins its makes

Proteins can perform a variety of functions

Refer to Table 13.6

A key category of proteins are enzymes

Accelerate chemical reactions within a cell

Can be divided into two main categories

Anabolic enzymes Synthesize molecules and macromolecules

Catabolic enzymes Break down large molecules into small ones

Important in generating cellular energy

Functions of Proteins

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13-40

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Estructura de tRNA

Estructura primaria

Estructura secundaria

Estructura terciaria

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Proceso de cargar el tRNA con aminocido correspondiente

Catalizado por aminoacyl-

tRNAsintetaza

Una sintetaza para cada

aminocido

Primer paso: activacin del

aminocido

Segundo paso: aminocido

se pasa de la enzima al tRNA

correspondiente

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Otros puntos importantes del tRNA:

Nomenclatura:

amino acid-tRNAaa

methionine-tRNAmet

Las aminoacyl-tRNA sintetazas son bien especificas para el

aminocido y el tRNA en su sitio activo.

Estas enzimas tambin tienen actividad verificadora para

asegurar que el anticodn en el tRNA corresponda con el

aminocido correcto.

tRNA de iniciacin en bacterias es especial

fMet-tRNAfMet

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Reconocimiento del tRNA por las tRNA sintetazas

Igual en todos los tRNA, no es utilizado

para el reconocimiento por la tRNAsintetaza

Utilizados por las tRNA

sintetazas para distinguir

Estructura 3D tambin es

importante para el reconocimiento

por tRNA sintetaza

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Componentes de traduccin

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Iniciacin-Tres pasos

Unin del ribosoma con el mRNAen

AUG requieresecuencia Shine-

Dalgarno

GTP, Mg, tRNAfMET

IF3 facilita interaccin

entre mRNA y 30S

IF2 se une a GTP y a fMet-tRNA y

estimula su unin con subunidad

grande del ribosoma, una vez se une

large subunit, IF-2 hidroliza GTP y

comienza elongacin

Complejo de iniciacin

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Secuencias Shine-Dalgarno

Secuencia Shine-Dalgarno es rica

en purinas.

16S rRNA es rica en pirimidinas.

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ElongacinLa unin de las dossubunidades crea

el sitio A y el sitio P

Nuevo tRNAentra a sitio A

Seforma enlace pptido por la

actividad de peptidyl transferasa entRNA desitio A

Saleel primer tRNA por sitio E

Translocacion del mRNA, segundotRNA pasa a sitio P

Entra nuevo tRNA a sitio A, nuevo ciclo

deelongacin

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TerminacinPresencia de un codn de terminacin en el

mRNA permite la actuacin de GTP-release factor

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Un experimento para probar que la

interaccin de Shine Dalgarno con el rRNAes importante para iniciacin

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Una vez se produce la protena esta debe

Desplazarse al lugar adecuado

Encontrarse con otras proteinas que regulen suactividad

Encontrarse con sus sustratos