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Molecular and Cellular Biology

3. The Cell – From Genes to Proteins

key processes

Prof. Dr. Klaus Heese

ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum

Centrosome

CYTOSKELETON:Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

MitochondrionLysosome

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

Animal Cell ((eukaryotic cell) -----> compare with prokaryotic cell)

NUCLEUSNuclear envelopeNucleolusChromatin

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Ribosomes

Central vacuole

MicrofilamentsIntermediate filamentsMicrotubules

CYTO-SKELETON

Chloroplast

PlasmodesmataWall of adjacent cell

Cell wall

Plasma membrane

Peroxisome

Mitochondrion

Golgiapparatus

Plant CellMonomers

vs

Polymers:

defines

cell feature

&

cell metabolism

Essential Bio-Engineering-related Bio-MoleculesOverview of four basic molecular genetic processes

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Alternative representations of a nucleic acid strand illustrating its chemical directionality.

by convention, a polynucleotide is always written 5’--->3’ direction.

Single-Strand DNA

Double-Strand DNA

The temperature at which DNA denatures increases with the proportion of GC-pairs. The higher GC%, the higher Tm.

DNA supercoils can be removed by cleavage of one strand

RNA secondary and tertiary structures

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RNA-synthesis:5’--->3’

RNA polymerase

DNA ---> RNA

Three stages in Transcription

Structure of the 5’ methylated cap of eukaryotic mRNA

Splicing: RNA processing to produce functional mRNA in eukaryotes

Threeroles of RNA

in Protein Synthesis(Translation)

mRNA, tRNA & rRNA

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read 5’ ---> 3’

Amino Acids

Genetic Code

Three possible open reading frames (start codons not shown)

Specific Aminoacyl-tRNA Synthethases activate Amino Acids by covalently linking them to tRNAs

Structure of tRNAs

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The general structure of ribosomes in prokaryotes and eukaryotes

Homogenization

TECHNIQUE

HomogenateTissuecells

1,000 g(1,000 times theforce of gravity)

10 min Differential centrifugationSupernatant pouredinto next tube

20,000 g20 min

80,000 g60 minPellet rich in

nuclei andcellular debris

Pellet rich inmitochondria(and chloro-plasts if cellsare from a plant)

Pellet rich in“microsomes”(pieces of plasmamembranes andcells’ internalmembranes)

150,000 g3 hr

Pellet rich inribosomes

Ph/CHCl3 – H2O-bufferSeparation of Proteins vs28S rRNA18S rRNA

5S rRNA

Lab methods

for

Ribosome isolation

DNA synthesis Bidirectional mechanism of DNA replication

A summary of transcription and translation in a eukaryotic cell

TRANSCRIPTION

RNA is transcribedfrom a DNA template.

DNA

RNApolymerase

RNAtranscript

RNA PROCESSING

In eukaryotes, theRNA transcript (pre-mRNA) is spliced andmodified to producemRNA, which movesfrom the nucleus to thecytoplasm.

Exon

RNA transcript(pre-mRNA)

Intron

NUCLEUS

FORMATION OFINITIATION COMPLEX

After leaving thenucleus, mRNA attachesto the ribosome.

CYTOPLASM

mRNA Growingpolypeptide

Ribosomalsubunits

Aminoacyl-tRNAsynthetase

Aminoacid

tRNAAMINO ACID ACTIVATION

Each amino acidattaches to its proper tRNAwith the help of a specificenzyme and ATP.

Activatedamino acid

TRANSLATION

A succession of tRNAsadd their amino acids tothe polypeptide chainas the mRNA is movedthrough the ribosomeone codon at a time.(When completed, thepolypeptide is releasedfrom the ribosome.)

AnticodonA A AU G G U U U A U G

E A

Ribosome

1

5¢

5¢

3¢

Codon

2

3 4

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What is a gene? revisiting the question

• A gene is a region of DNA whose final product is either a polypeptide or an RNA molecule –

• A gene is the molecular unit of heredity ( = DNA // or RNA) of a living organism that codes for a protein or a (functional) RNA.

What is a gene? revisiting the question