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Week6 The molecular basis for growth and
reproduc9on
1. Review: Central dogma (and beyond)
2. Structure of DNA and its replica9on
3. Transla9ng the gene9c code
4. Using ribosomal RNA to infer the evolu9onary rela9onships
DNA polymerase
RNA polymerase
Ribosome, mRNA, tRNA
spontaneous; aided by molecular chaperons folding
Reverse Transcriptase (e.g. HIV)
Post-‐transla9onal protein modifica9on (e.g. cell signaling, cancer)
Prions (e.g. in BSE)
Non-‐ribosomal pep9des (e.g. cyclosporine)
Ribozymes (i.e. RNA enzymes)
Epigene9cs (i.e. modifica9on of DNA packing)
RNA interference (i.e. RNA-‐mediated gene silencing)
RNA modifica9on
Many interes9ng processes occur beyond the central dogma
Splicing
Transposable elements
Gene9c informa9on, the structure of DNA
-‐ A pairs T, G pairs C (hydrogen bonds) -‐ phosphate-‐sugar backbone (nega9ve charge) -‐ The two strands run an9parallel
Double helix
Crick & Watson: “The secret of life”
-‐> Homework paper
“Semi-‐conserva9ve copying” “right handed”
chirality
X-‐ray fiber diffrac9on by Rosalind Franklin
Example: Transla9ng the gene9c code
e.g. DNA: 5’-TGCGCCCTTACAGAATGCCATTGA-3’! mRNA: !5’-UGCGCCCUUACAGAAUGCCAUUGA-3’!Protein: N’-C A L T E C H *-C’!
Rules of transla9ng the code: -‐ Non-‐overlapping triplet code -‐ Redundant -‐ 1 start and 3 stop signals
4 nucleo9des, 20 amino acids
The ribosome translates the gene9c code into protein
rRNA sequences are highly conserved -‐> evolu9onary rela9onship between species
S: Svedberg unit of sedimenta9on
Bacteria, Archaea
makes pep(de bond
selects correct tRNA
The small ribosomal subunit “reads” the mRNA, the large subunit synthesizes the protein
X
X
X
X MOVIE
Protein synthesis by the ribosome
Example: The 16S/18S RNA sequence is highly conserved between species
-‐ The core of the RNA molecules is highly conserved -‐ Differences can be used to infer evolu9onary rela9onships (‘tree of life’)
Bacteria (16S) Archaea (16S)
Eucarya (18S)
Region ‘decoding’ the mRNA
Rela9onship between structure and func9on in proteins
Primary structure: Sequence of amino acids connected by pep9de bonds
Secondary structure: Sequence of structural mo9fs formed by regular hydrogen bonds of the pep9de bonds (alpha helix, beta sheet)
Ter9ary structure: 3D atomic model of the protein including cofactors (e.g. ions).
spacefill representa9on cartoon representa9on
GWQAEIVTEFSLL NEMVDVDPQGIL KCVDGR ……
hydrogen bonds formed by the protein backbone
α β
Quaternary structure: Molecular assemblies
e.g. ribosomes
The end
Small subunit (mainly 16S RNA)
When the correct tRNA is binding to the mRNA codon, 16S rRNA closes and triggers pep9de bond forma9on
Region where correct tRNA is detected
Why is 16S RNA highly conserved in all species?
View from side
Region where pep9de bond is made
Week8:
Obtaining the the 16S RNA sequence of a bacterium
Sample -‐> DNA isola9on (Proper9es: DNA nega9ve, large; remove RNA with RNase)
-‐> Amplifica9on of the 16S RNA gene (PCR)
-‐> DNA sequencing
Polymerase chain reac9on (PCR)
Key insights (1960-‐early 80s):
-‐ DNA helix separated when temperature increases
-‐ DNA polymerase copies DNA at lower temperature
-‐ Heat-‐stable DNA polymerase discovered
Yellowstone
The ribosome orchestrates protein synthesis using mRNA, tRNA and addi9onal proteins (transla9on factors)
4 main phases of transla9on: 1. Ini9a9on 2. Elonga9on 3. Release 4. Recycling MOVIE
Chemistry and physics are the founda9on of biology
Enzymes catalyze chemical reac9ons that are unfavorable.
Physical techniques are used to visualize/measure biological processes.
The tools of molecular biology, the combina9on of chemistry and gene9cs, have revolu9onized our ability to inves9gate and control cells.
Polymerase chain reac9on (PCR)
-‐> Homework assignment: DNA replica9on Youtube Video
The ribosome as an example for a ‘molecular machine’
2 key func9ons:
-‐ select correct amino acid
-‐ form covalent bond between growing protein and next amino acid
Transla9on involved many proteins and several large RNA molecules working together in a coordinated manner.
Transfer RNA (tRNA) “adapter”
Messenger RNA (mRNA)
Amino Acid