Chemicals of lifeCell Membrane

Bi 1aBi 1h

Modified from Kim Foglia

I will be able to:

(Bi 1a) Know that cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

(Bi 1h) Know that most macromolecules ( polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors.

The Chemistry of Life

What are living creatures made of?

Why do we have to eat?

Major chemicals->96% ( non-metal, covalent bonds)

carbon (C) oxygen (O) hydrogen (H) nitrogen (N) Phosphorus (P) Sulfur (s)

Elements of Life

Macromolecules of Life Put C, H, O, N,P,S together in

different ways to build living organisms

What are bodies made of? carbohydrates ▪ sugars & starches

proteins fats (lipids) nucleic acids▪ DNA, RNA

Why do we eat? We eat to take in more of these

chemicals Food for building materials▪ to make more of us (cells)▪ for growth▪ for repair

Food to make energy▪ calories▪ to make ATP

ATP

Water 65% of your body is H2O water is inorganic ▪ doesn’t contain carbon

Rest of you is made of carbon (valence electrons? bonds?) organic molecules▪ carbohydrates▪ proteins▪ fats▪ nucleic acids

Don’t forget water

2006-2007

How do we make these molecules?

We build them!

What are these 4 macromolecules? Carbohydrates

Nucleic Acids

Proteins

Lipids

Small molecules = building blocks/ monomers

Bond them together = polymers

Building large organic molecules

Building important polymers

sugar – sugar – sugar – sugar – sugar – sugar

nucleotide – nucleotide – nucleotide – nucleotide

Carbohydrates = built from sugars

Proteins = built from amino acids

Nucleic acids (DNA) = built from nucleotides

aminoacid

aminoacid– amino

acid– aminoacid– amino

acid– aminoacid–

LIPID ( fat) is an exceptionBuilding blocks of fat are not

considered as monomers.

One common type is made up of:

3 fatty acid molecules + 1 glycerol molecule= 1 triglyceride

How to build large molecules

Synthesis building bigger

molecules from smaller molecules

Monomer+monomer= POLYMER

+ATP

Example of synthesis

amino acids protein

amino acids = building blockprotein = polymer

Proteins are synthesized by bonding amino acids

How to take large molecules apart

Digestion taking big molecules apart getting raw materials▪ for synthesis & growth

making energy (ATP)▪ for synthesis, growth & everyday functions

+

ATP

Example of digestion

starch glucoseATP

ATP

ATP

ATP

ATP

ATPATP

Starch is digested to glucose

4 MacromoleculesPROCESS ORGANELLES

CARBOHYDRATES

cellular respiration, photosynthesis

Mitochondria, chloroplast

NUCLEIC ACIDS

DNA transcription, translation

Nucleus

PROTEINS Protein synthesis, cell transport

Ribosomes, ER, Golgi apparatus, cell membrane

LIPIDS Cell transport

Cell membrane

2003-2004

Lipids: Fats & Oils

2003-2004

Lipids Examples

Fats oils waxes hormones

▪ testosterone (male)▪ estrogen (female)

Lipids Function:

energy storage ▪ very concentrated▪ twice the energy as carbohydrates!

cell membrane cushions organs insulates body▪ think whale blubber!

2003-2004

Structure of Fat3 fatty acid + 1 glycerol= triglyceride

not a chain (polymer) = just a “big fat molecule”

The Cell Membrane

Cell membrane defines cell

Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick

Controls traffic in & out of the cell allows some substances to cross more

easily than others▪ hydrophobic (nonpolar) vs. hydrophilic

(polar)

Polar and non-polar

POLAR: unequal sharing of electrons

NON-POLAR: equal sharing of electrons

Phospholipids

Fatty acid

Phosphate

Phosphate head hydrophilic

Fatty acid tails HydrophobicOil & water don’t mix!

Arranged as a bilayer

Aaaah, one of thosestructure–functionexamples

“repelled by water”

“attracted to water”

Arranged as a Phospholipid bilayer

polarhydrophilicheads

nonpolarhydrophobictails

polarhydrophilicheads

Serves as a cellular barrier / borderH2Osugar

lipids

salt

waste

impermeable to polar molecules

Cell membrane must be more than lipids…

In 1972, S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer

It’s like a fluid…It’s like a mosaic…It’s the Fluid Mosaic Model!

Permeability to polar molecules?

Membrane becomes semi-permeable via protein channels specific channels allow specific

material across cell membrane

inside cell

outside cell

sugaraaH2O

saltNH3

Proteins* in the cell membrane Transmembrane proteins embedded in

phospholipid bilayer ( fat) are like “gates” create semi-permeable channels ( or tunnels )lipid bilayermembrane

protein channelsin lipid bilayer membrane

Proteins Building block =

aminoacid

aminoacid– amino

acid– aminoacid– amino

acid–

—N—H

H

H|—C—| C—OH

||O

variable group

amino acids

20 different amino acidsThere’s20 of us…like 20 differentletters in analphabet!Can make lots of differentwords

POLYPEPTIDE Amino acid (monomer) chains in a

peptide bond => polypeptide (polymer)

Each amino acid is different some “like” water & dissolve in it some “fear” water & separate

from it

amino acid amino acid amino acid amino acid amino acid

pepsin

For proteins: SHAPE matters!

collagen

Proteins fold & twist into 3-D shape that’s what happens in the cell!

Different shapes = different jobs

hemoglobingrowthhormone

It’s SHAPE that matters!

Proteins do their jobs, because of their shape

Unfolding a protein destroys its shape wrong shape = can’t do its job unfolding proteins = “denature”▪ temperature▪ pH (acidity)

folded

unfolded“denatured”

In Biology,it’s the SHAPEthat matters!

2007-2008

Why areproteins the perfect molecule to build structures in the cell membrane?

Classes of amino acidsWhat do these amino acids have in

common?

nonpolar & hydrophobic

Water-loving amino acids Hydrophillic

“water loving” amino acids try to stay in water in cell

the protein folds

Classes of amino acidsWhat do these amino acids have in

common?

polar & hydrophilic

I like thepolar onesthe best!

Water-fearing amino acids Hydrophobic

“water fearing” amino acids try to get away from water in cell

the protein folds

Within membrane nonpolar amino

acids ▪ hydrophobic ▪ anchors protein

into membrane On outer surfaces

of membrane in fluid polar amino acids ▪ hydrophilic▪ extend into

extracellular fluid & into cytosol

Polar areasof protein

Nonpolar areas of protein

Proteins have polar & non-polar areas!!!

Many Functions of Membrane ProteinsOutside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

Cell adhesion

“Antigen”

“Channel”

Membrane Proteins Proteins determine membrane’s specific

functions cell membrane & organelle membranes each

have unique collections of proteins Classes of membrane proteins:

peripheral proteins ▪ loosely bound to surface of membrane▪ ex: cell surface identity marker (antigens)

integral proteins ▪ penetrate lipid bilayer, usually across whole membrane ▪ transmembrane protein▪ ex: transport proteins▪ channels, permeases (pumps)

Membrane carbohydrates* attached to proteins-> glycoprotein

Play a key role in cell-cell recognition ability of a cell to distinguish one cell

from another▪ antigens

important in organ & tissue development

basis for rejection of foreign cells by immune system

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer

Extracellular fluid

Cholesterol

Cytoplasm

Glycolipid

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model