Transcript Four Levels of Protein Structure

Molecules of Life
Molecules of Life
 Molecules of life are synthesized by living cells
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Carbohydrates
Lipids
Proteins
Nucleic acids
Organic Compounds
 Consist primarily of carbon and hydrogen atoms
• Carbon atoms bond covalently with up to four
other atoms, often in long chains or rings
 Functional groups attach to a carbon backbone
• Influence organic compound’s properties
An Organic Compound: Glucose
 Four models
Functional Groups:
The Importance of Position
Processes of Metabolism
 Cells use energy to grow and maintain
themselves
 Enzyme-driven reactions build, rearrange, and
split organic molecules
Building Organic Compounds
 Cells form complex organic molecules
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Simple sugars → carbohydrates
Fatty acids → lipids
Amino acids → proteins
Nucleotides → nucleic acids
 Dehydration synthesis combines monomers to
form polymers
Dehydration synthesis and Hydrolysis
Carbohydrates –
The Most Abundant Ones
 Three main types of carbohydrates
• Monosaccharides (simple sugars)
• Oligosaccharides (short chains)
• Polysaccharides (complex carbohydrates)
 Carbohydrate functions
• Instant energy sources
• Transportable or storable forms of energy
• Structural materials
Oligosaccharides: Sucrose
Complex Carbohydrates:
Starch, Cellulose, and Glycogen
Structure of
cellulose
c Glycogen. In animals, this
polysaccharide is a storage form
for excess glucose. It is
especially abundant in the liver
and muscles of highly active
animals, including fishes and
people.
Greasy, Oily – Must Be Lipids
 Lipids
• Fats, phospholipids, waxes, and sterols
• Don’t dissolve in water
• Dissolve in nonpolar substances (other lipids)
 Lipid functions
• Major sources of energy
• Structural materials
• Used in cell membranes
Fats
 Lipids with one, two, or three fatty acid tails
• Saturated
 Triglycerides (neutral fats )
• Three fatty acid tails
• Most abundant animal fat (body fat)
• Major energy reserves
Triglyceride Formation
Phospholipids
 Main component of
cell membranes
• Hydrophilic head,
hydrophobic tails
Waxes
 Firm, pliable, water repelling, lubricating
Steroids: Cholesterol
 Membrane components; precursors of other
molecules (steroid hormones)
Protein Structure
 Built from 20 kinds of amino acids
Four Levels of Protein Structure
1. Primary structure
• Amino acids joined by peptide bonds form a
linear polypeptide chain
2. Secondary structure
• Polypeptide chains form sheets and coils
3. Tertiary structure
• Sheets and coils pack into functional domains
Four Levels of Protein Structure
4. Quaternary structure
• Many proteins (e.g. enzymes) consist of two or
more chains
Levels of Protein Structure
Levels of Protein Structure
Levels of Protein Structure
Levels of Protein Structure
Why is Protein Structure
So Important?
 Protein structure dictates function
 Sometimes a mutation in DNA results in an
amino acid substitution that alters a protein’s
structure and compromises its function
• Example: Hemoglobin and sickle-cell anemia
Normal Hemoglobin Structure
VALINE
HISTIDINE
LEUCINE THREONINE PROLINE
b One amino acid substitution results in the
abnormal beta chain in HbS molecules. Instead
of glutamate, valine was added at the sixth
position of the polypeptide chain.
c Glutamate has an overall negative charge; valine
has no net charge. At low oxygen levels, this
difference gives rise to a water-repellent, sticky
patch on HbS molecules. They stick together
because of that patch, forming rod shaped clumps
that distort normally rounded red blood cells into
sickle shapes. (A sickle is a farm tool that has a
crescent-shaped blade.)
VALINE
sickle cell
normal cell
GLUTAMATE
Clumping of cells in bloodstream
Circulatory problems, damage to brain,
lungs, heart, skeletal muscles, gut, and
kidneys
Heart failure, paralysis, pneumonia,
rheumatism, gut pain, kidney failure
Spleen concentrates sickle cells
Spleen enlargement
Immune system compromised
Rapid destruction of sickle cells
d Melba Moore, celebrity spokesperson for sickle-cell anemia
organizations. Right, range of
symptoms for a person with two
mutated genes for hemoglobin’s
beta chain.
Anemia, causing weakness,fatigue,
impaired development,heart chamber
dilation
Impaired brain function, heart failure
Denatured Proteins
 If a protein unfolds and loses its threedimensional shape (denatures), it also loses its
function
 Caused by shifts in pH or temperature, or
exposure to detergent or salts
• Disrupts hydrogen bonds and other molecular
interactions responsible for protein’s shape
Nucleotides, DNA, and RNAs
Nucleotide structure, 3 parts:
• Sugar
• Phosphate group
• Nitrogen-containing base
Nucleotide Functions:
Reproduction, Metabolism, and Survival
 DNA and RNAs are nucleic acids, each
composed of four kinds of nucleotide subunits
 ATP energizes many kinds of molecules by
phosphate-group transfers
Nucleotides of DNA
DNA, RNAs, and Protein Synthesis
 DNA (double-stranded)
• Encodes information about the primary structure
of all cell proteins in its nucleotide sequence
 RNA molecules (usually single stranded)
• Different kinds interact with DNA and one another
during protein synthesis
covalent
bonding in
carbon
backbone
hydrogen bonding
between bases