life - university of texas at austin · misfold. minimum requirements for life proteins and nucleic...
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Life
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What is necessary for life?Most life familiar to us: Eukaryotes
First appeared ~ 1.5 - 2 × 109 years ago Requirements: DNA, proteins, lipids, carbohydrates, complex structure, ~ 104 - 105 genes
FREE LIVINGOr Parasites
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Prokaryotes (Bacteria and Archaea)
Requirements: DNA, protein, lipids, carbohydrates, simpler structure, few thousand genes
FREE LIVINGOr Parasites
First appeared ~ 3 - 4 ×109 years ago
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Viruses
DNA, protein RNA, protein, maybe lipid (e.g., HIV)
All (?) are parasites. Are they alive?
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The tobacco-mosaic virus is made up of a strand of nucleic acid encased in a rod of one kind of protein.
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Even Simpler
Viroids Bare, single-strandedRNA
PrionsMisfolded proteinsCan induce others to Misfold.
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Minimum Requirements for Life
Proteins and Nucleic Acids for simplest possible life.
Or maybe only one?Lipids and Carbohydrates for any thing
more complex than a virus.These are all macromolecules.
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MacromoleculesProteins made of amino acids (20 kinds used in proteins)Construction and catalysis (enzymes)Nucleic acids made of nucleotides
base sugar phosphate
Polymers made of Monomers
H, C, N, O (S)
H, C, N, O (P)
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Carbohydrates made of sugarsEnergy (food) + structure [starch] [cellulose]
Lipids (hydrocarbons + carboxyl)Membranes + Energy [water-resistant]
H, C, O
H, C, (O)
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Sugar
Glucose
hydrocarboncarboxyl
Lipids
Fatty acid is composed of a hydrocarbon chain with a carboxyl group at one end
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Polysaccharides
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Proteins and Nucleic Acids
• Proteins– Structure– Enzymes (catalysts to control reactions)
• Nucleic Acids– Information – Replication of information: reproduction– Instructions for making proteins
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ProteinsMonomers are amino acids 20 kinds
HH
H
H H
N C C
O
O
a b c
Amino group
carboxyl group
Glycine
Amino group (hook)
carboxyl group (eye)
Schematic
Section of Protein
… …
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H
HN
H
C
O
Oeye end hook end Before
After
A Peptide Bond at the Chemical Level
H
H
N
H
C
O
O
eye end hook end
Note that a water molecule must be removed
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amino acids
protein
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A complex protein:
Involved in oxygen use Each circle is an amino acid
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Stripped down view Can you find the amino end and the carboxyl end?
Note the “heme”, containing iron.
Function depends on structure, which depends on folding, which depends on order of amino acid bases
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Nucleic Acids (DNA, RNA)
Made of sugars, phosphates, bases
Ribose Sugar5 C, 5 O, 10 H
Sugar Schematic
Deoxy Ribose
Ribonucleic acid (RNA) uses ribose sugar;Deoxyribonucleic acid (DNA) uses deoxyribose sugar
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phosphate
sugars & phosphates linkedphosphodiester bonds
Segment of side of ladder structure
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Nucleic Acids (cont.)
Bases: Carry Genetic Code
Purines
A
G
Adenine
Guanine
Equal numbers of C and N
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Pyrimidines
C U T
Cytosine Uracil / ThymineRNA / DNA
More C than N
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Bases in Nucleic acids: Purines and Pyrimidines
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Purines
Pyrimidines
Note Uracil
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Nucleic Acids (cont.)
Note that T replaces U in DNA
Segment of RNA
Segment of DNAPP
TAG
S S S
A C T
P
S S S
P
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Deoxyribose
Phosphate
Deoxyribonucleic Acid (DNA)
At the Chemical Level
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The two strands of DNA form a double helix, connected between bases by hydrogen bonds
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Model of a short segment of DNA showing all the atoms
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Hydrogen Bonds (weak) connect the bases across the two sides of DNA
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Segment of DNA
… …
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Further wrapping to make compact chromosome
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Information Storage
• Nucleic acids store information• The information specifies proteins• The information can be replicated• This allows inheritance
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Base pairing rules
A - T (DNA) G - C- U (RNA)
⇒ Replication of order (reproduction)
Nucleic Acids and Proteins communicate through the Genetic Code
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Codons and Genes
Codon:A 3 base sequence that specifies an Amino Acid
Gene:A sequence of codons that specifies a Protein
e.g. tobacco mosaic virus 4 genesbacteria ~ 103 to 104 geneshuman cell ~ 23,000 genes
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For mRNA Genetic CodeFirst RNABase U C A G
Third RNA BASE
U
PhenylalaninePhenylalanineLeucineLeucine
SerineSerineSerineSerine
TyrosineTyrosineStopStop
CysteineCysteineStopTryptophan
UCAG
C
LeucineLeucineLeucineLeucine
ProlineProlineProlineProline
HistidineHistidineGlutamineGlutamine
ArginineArginineArginineArginine
UCAG
A
IsoleucineIsoleucineIsoleucineStart/Methionine
ThreonineThreonineThreonineThreonine
AsparagineAsparagineLysineLysine
SerineSerineArginineArginine
UCAG
G
ValineValineValineValine
AlanineAlanineAlanineAlanine
Aspartic AcidAspartic AcidGlutamic AcidGlutamic Acid
GlycineGlycineGlycineGlycine
UCAG
Amino Acids
Second RNA Base
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Structure of a tRNA
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Translation
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Variations in the Code
1. “Wobble” BasesThe third base in a codon can sometimes vary.
tRNA mRNA U A or G G C or U
Comparison to genetic code ⇒ no change in amino acids
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For mRNA Genetic CodeFirst RNABase U C A G
Third RNA BASE
U
PhenylalaninePhenylalanineLeucineLeucine
SerineSerineSerineSerine
TyrosineTyrosineStopStop
CysteineCysteineStopTryptophan
UCAG
C
LeucineLeucineLeucineLeucine
ProlineProlineProlineProline
HistidineHistidineGlutamineGlutamine
ArginineArginineArginineArginine
UCAG
A
IsoleucineIsoleucineIsoleucineStart/Methionine
ThreonineThreonineThreonineThreonine
AsparagineAsparagineLysineLysine
SerineSerineArginineArginine
UCAG
G
ValineValineValineValine
AlanineAlanineAlanineAlanine
Aspartic AcidAspartic AcidGlutamic AcidGlutamic Acid
GlycineGlycineGlycineGlycine
UCAG
Amino Acids
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2. Some organisms use slightly different codes, with one or more changes in codon translation.
First seen in mitochondrial DNA.Now known in some nuclear DNA
The code has evolved since the last common ancestor (But not much).
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Summary
1. Atoms needed: H, C, O, N, small amounts of P (phosphorus), S (sulfur)
2. Two basic molecules needed for life: proteins, nucleic acids
3. Both are polymers - made of simpler monomers. The monomers function as words or letters of alphabet. Information is the key.
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Summary (cont.)
4. Proteins and nucleic acids closely linked at fundamental level. Communicate through genetic code. All organisms have almost the same genetic code. It must have originated very early in evolution of life.
5. In present day organisms, protein synthesis must be directed by nucleic acids, but nucleic acid reading or replication requires enzymes (proteins). Chicken-Egg problem
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Some Movies of Processes• From the Virtual Cell Animation collection,
Molecular and Cellular Biology Learning Center– http://vcell.ndsu.nodak.edu/animations/home.htm– Needs Windows media player
• Another option:– http://highered.mcgraw-hill.com/sites/0072507470/
student_view0/chapter3/– And look for mRNA synthesis and How translation works.