Life Lecture

8/13/2019 Life Lecture

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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 !109years ago

Requirements: DNA, proteins, lipids, carbohydrates,

complex structure, ~ 10

4

- 10

5

genes

FREE LIVINGOr Parasites


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Prokaryotes (Bacteria and Archaea)

Requirements: DNA, protein, lipids, carbohydrates,

simpler structure, few thousand genes

FREE LIVING

Or Parasites

First appeared

~ 3 - 4 !109years ago


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Viruses DNARNA

Proteins

Viroids, Prions?

Plasmids

RNA

Few hundred bases

Few thousand bases

Protein

Parasites


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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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Minimum Requirements for Life

Proteins and Nucleic Acids for simplest

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)

Construction and catalysis (enzymes)

Nucleic acids made of nucleotides

base sugar phosphate

Polymers and 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

Monomers are amino acids 20 kinds

HH

H

H H

N C C

O

O

a b c

Aminogroup

carboxyl

group

Glycine

Amino group(hook) carboxyl group(eye)

Schematic

Section of Protein


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H

H

N

H

C

O

O

eye 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 oxygenuse Each circle is an

amino acid


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Stripped down view

Can you find the

amino end and thecarboxyl end?

Note the heme,

containing iron.

Function depends

on structure, which

depends on folding,

which depends onorder of amino acid

bases


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Nucleic Acids (DNA, RNA)

Made of sugars, phosphates, bases

Ribose Sugar

5 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 / Thymine

RNA / 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.)

Segment of RNA

Segment of DNA

Note that Treplaces U in DNA


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Deoxyribose

Phosphate

Deoxyribonucleic Acid (DNA)

At the Chemical Level


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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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The two strands of DNA form a double helix,

connected between bases by hydrogen bonds


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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 G - C

- U

" Replication of order (reproduction)

Nucleic Acid - Protein Genetic Code


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Codon

3 base sequence specifies an Amino Acid

GeneSequence of codons specifies a Protein

a gene specifies a protein

e.g. tobacco mosaic virus 4 genesbacteria ~ 10

3genes

human cell ~ 25,000genes

(update)


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For mRNA Genetic Code

U

C

A

G

Glycine

Glycine

Glycine

Glycine

Aspartic Acid

Aspartic Acid

Glutamic Acid

Glutamic Acid

Alanine

Alanine

Alanine

Alanine

Valine

Valine

Valine

ValineG

U

C

AG

UC

A

G

U

C

A

G

Third

RNA

BASE

Serine

Serine

ArginineArginine

Asparagine

Asparagine

LysineLysine

Threonine

Threonine

ThreonineThreonine

Isoleucine

Isoleucine

IsoleucineStart/MethionineA

ArginineArginine

Arginine

Arginine

HistidineHistidine

Glutamine

Glutamine

ProlineProline

Proline

Proline

LeucineLeucine

Leucine

LeucineC

Cysteine

Cysteine

Stop

Tryptophan

Tyrosine

Tyrosine

Stop

Stop

Serine

Serine

Serine

Serine

Phenylalanine

Phenylalanine

Leucine

LeucineU

GACU

First

RNA

Base

Amino Acids


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Structure of a tRNA


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Translation


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Variations in the Code

1. Wobble Bases

The third base in a codon can sometimes vary.

tRNA mRNA U A or G

G C or U

Comparison to genetic code "no changein amino acids


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For mRNA Genetic Code

U

C

A

G

Glycine

Glycine

Glycine

Glycine

Aspartic Acid

Aspartic Acid

Glutamic Acid

Glutamic Acid

Alanine

Alanine

Alanine

Alanine

Valine

Valine

Valine

ValineG

U

C

AG

UC

A

G

U

C

A

G

Third

RNA

BASE

Serine

Serine

ArginineArginine

Asparagine

Asparagine

LysineLysine

Threonine

Threonine

ThreonineThreonine

Isoleucine

Isoleucine

IsoleucineStart/MethionineA

ArginineArginine

Arginine

Arginine

HistidineHistidine

Glutamine

Glutamine

ProlineProline

Proline

Proline

LeucineLeucine

Leucine

LeucineC

Cysteine

Cysteine

Stop

Tryptophan

Tyrosine

Tyrosine

Stop

Stop

Serine

Serine

Serine

Serine

Phenylalanine

Phenylalanine

Leucine

LeucineU

GACU

First

RNA

Base

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 commonancestor (But not much).


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Summary (cont.)

4. Proteins and nucleic acids closely linked atfundamental level. Communicate throughgenetic code. All organisms have almostthe same genetic code. It must have

originated very early in evolution of life.

5. In present day organisms, protein synthesismust be directed by nucleic acids, but

nucleic acid reading or replication requiresenzymes (proteins). Chicken-Egg problem


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Some Movies of Processes Animation of transcription (making mRNA)

http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm

Animation of translation (making protein) http://vcell.ndsu.nodak.edu/animations/translation/movie.htm

Both from Virtual Cell Animation collection,Molecular and Cellular Biology Learning

Center

Life Lecture

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