Lecture 1: Cell Bio

Different Cell Types

•  Humans have at least 200 different cell types. •  Yet, all cells share some basic components…

Cellular Similarities: Basic Cell Anatomy •  Plasma Membrane - lipid bilayer •  Cytoplasm •  Cytoskeleton - actin

microfilaments, microtubules, IFs •  Nucleus - nuclear envelope,DNA •  Ribosomes - protein synthesis •  Rough ER - protein synthesis,

glycosylation •  Smooth ER - lipid and steroid

synthesis/metabolism, receptor attachment,enzyme storage/prod, carb metab, Ca regulation, G6P (gluconeogenesis)

•  Golgi Apparatus - sorting, modifying & packaging proteins, ↓ apoptosis

•  Lysosomes - digests proteins with acidic enzymes

•  Mitochondria - makes ATP, FA oxidation/synth, cholesterol→ steroids, ↑ apoptosis, Ca reg

•  Centrosome with Centrioles - anchor for microtubules esp during mitosis

THE PLASMA MEMBRANE Composition, Permeability & Movement of substances across

The Plasma Membrane

1.  The lipid bilayer is made of these lipids:

1.  phospholipids (75%) 2.  cholesterol (20%) 3.  glycolipids (5%)

2.  Proteins are embedded in the lipids

The Plasma Membrane

Phospholipids, cholesterol, glycolipids, membrane proteins

Permeability of the Lipid Bilayer •  Freely Permeable to

small, or uncharged, non-polar, molecules: –  Steroids, O2, CO2, N2,

Fat-soluble vit: A,D,E,K

•  Slightly Permeable to small and/or polar molecules eg: –  Urea, Water, Ethanol

•  Impermeable to large or charged molecules such as –  sugar (Glucose), amino

acids, nucleotides, proteins, Ions (Na+, Cl-)

Green arrows can simply diffuse across the membrane. Red arrows need facilitation to get across

FYI: Sizes of some molecules

•  Charged ions (Cl-, K+) and Larger molecules (glucose..) cannot simply diffuse through the lipid bilayer.

•  They cannot get into or out of a cell without facilitation.

What drives the movement of the small uncharged molecules

across a cell membrane?

Concentration Gradient

•  Substances or Solutes passively diffuse through a semipermeable membrane from high concentration to low concentration, seeking equilibrium

Phospholipids are an AMPHIPATHIC (ie both polar and non-polar) substance The Phosphate Heads are polar, or slightly charged, so it can form hydrogen

bonds with water, thus, are attracted to water, or, Hydrophilic. The Fatty Acid Tails are non-polar, or uncharged. They are attracted to other

lipids. They are repelled by water or Hydrophobic.

75% (Amphipathic) Phospholipids

MEMBRANE PROTEINS Channels, Carriers, Transporters, Active & Passive transport

Functions of Membrane Proteins

•  Receptors •  Ion channels •  Transporters

•  Enzymes •  Cell Identity Markers

•  Linkers

Integral & Peripheral Membrane Proteins

1.  Integral (Transmembrane) Proteins: extend through lipid bilayer 2.  Peripheral Proteins: attached to inside or outside surface of

plasma membrane

1. Passive Transport •  Its called “PASSIVE”

because NO ENERGY IS REQUIRED for substances to diffuse down their gradients.

A.  In Simple DIFFUSION,

substances pass directly through the lipid bilayer – no protein is required

B.  Facilitated DIFFUSION the substance is either too big or charged and thus requires a channel protein or a carrier protein to enter the cell

B. Proteins that Facilitate Diffusion

•  Channel Proteins eg ion channel

•  DO NOT CHANGE SHAPE •  But, may be GATED

–  ligand-gated –  voltage-gated –  stretch-gated

•  Carrier = Transport Proteins eg glucose transporter

•  Transport molecules down concentration gradient by BINDING & CHANGING SHAPE

Passive vs. Active Transport: Is energy required to

cross the cell’s membrane?

1.  Passive Transport –  NO ENERGY IS

REQUIRED –  Molecules flow from high

concentration to low concentration or down their electrochemical gradients

2.  Active Transport

–  REQUIRES ENERGY (usually ATP)

–  Molecules are pushed AGAINST their gradients

In which direction does a charged solute want to move? Electrochemical Gradient

•  Electrical Gradient - charged substances are drawn to areas of opposite charge

+ •  Concentration

gradient - substances tend to go from high concentration to low concentration

= •  Electrochemical

gradient - net gradient for a substance depends on both concentration & charge

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2. Active Transport (Requires ENERGY)

ENERGY is needed to transport substances AGAINST their concentration or electrochemical gradients

•  1°Active Transport requires chemical energy (eg hydrolysis of ATP) to

move a substance against its gradient

•  2°Active Transport uses electrochemical gradient of one substance (usually Na) to transport a second substance against its gradient –  Symport - 2 substances move in same direction –  Antiport - 2 substances move in opposite directions

The Classic example of Active Transport: Na /

K / ATPase pump

•  Pumping both Na & K, AGAINST their ELECTROCHEMICAL GRADIENTS requires energy.

•  Binding of Na, triggers hydrolysis of ATP. Breaking the ATP bonds releases Energy + ADP +Pi

•  The energy changes the shape of the transporter to pump out the 3 Na –  3 Na+ out , 2 K+ in –  Creates a Net + charge outside cell, keeps Na+ out of cells

VESICULAR TRANSPORT Exocytosis & Endocytosis

Vesicular Transport •  Vesicles (like bubbles) transport

large or polar substances across the cell membrane. ALL REQUIRE ATP

1.  ENDOCYTOSIS - large substances (eg dead bacteria) enter the cell by invagination & pinching off a little bit of the plasma membrane –  Phagocytosis, pinocytosis, –  Receptor-mediated endocytosis

2.  EXOCYTOSIS - large substances (eg neurotransmitters) exit the cell via vesicles that fuse with the plasma membrane.

3.  Transcytosis - cross cell. large substances enter one side of cell and leave the other side

OSMOSIS Movement of SOLVENT across membranes

A special case of Diffusion OSMOSIS: Movement of WATER

•  Movement of SOLVENT ie WATER through a semipermeable membrane •  Water moves towards areas with more solute (or higher osmolarity) •  Water moves by simple diffusion or through special membrane proteins,

called aquaporins

Osmosis & Tonicity Since water follows solute: •  if there is more solute is inside

the cell, ie the interstitial fluid is hypotonic to the cell, water will enter the cell and it will swell or burst: hemolysis

•  If there is more solute outside the cell, in the interstitial fluid ie interstitial fluid is hypertonic to the cell, water exits the cell and it crenates

•  Under normal conditions, the osmotic pressure of the interstitial fluid = osmotic pressure of the cell’s cytosol So…water moves into and out of a cell at the same rate.

Summary of Movement across the Cell Membrane

•  Movement of solutes across a cell membrane can happen by: –  Passive Transport

•  Simple Diffusion – directly across the lipid bilayer •  Facilitated Diffusion – needs channel & carrier but no energy

–  Active Transport •  1° (requires ATP) •  2° - symport & antiport (uses another substance’s gradient)

–  Vesicular Transport •  Endocytosis •  Exocytosis •  Transcytosis

•  Movement of the solvent (not the solute) –  Osmosis (movement of water)

PROTEIN SYNTHESIS How a cell makes its proteins

Membrane Proteins & the Fluid Mosaic

•  Protein positions and amounts are not static in the membrane but are constantly moving, changing places, adding or eliminating pieces like a mosaic that is fluid

2 Steps of Protein Synthesis •  Step 1: in Nucleus

TRANSCRIPTION –  DNA is transcribed

into mRNA

•  Step 2: in Ribosome TRANSLATION –  mRNA is translated

into a protein –  Ribosomes can be

•  free in the cytoplasm •  or attached onto the

Rough Endoplasmic Reticulum (RER)

The Nucleus contains Chromatin

•  In a non-dividing cell nucleus, the chromatin is loose and diffuse •  Chromatin is a strand of nucleosomes with linker DNA in between. •  A nucleosome is DNA wrapped around 8 histone proteins •  Only when a cell divides, the chromatin folds and packs tightly into

Chromosomes

A Nucleotide consists of: 1.  a Phosphate group, 2.  a Deoxyribose Sugar, 3.  And a Nitrogenous Base

–  Adenine (A) –  Guanine (G) –  Thymine (T) –  Cytosine (C)

The Base Pairs are: –  Adenine – Thymine –  Cytosine – Guanine

DNA consists of Nucleotides

TRANSCRIPTION: DNA codes for RNA

•  A gene is a section of DNA that codes for a protein.

•  RNA polymerase binds to a gene’s promoter region on the DNA.

•  RNA pol. unwinds the double helix & pairs RNA nucleotides to DNA nucleotides from one strand

•  When the RNA pol. reaches a

terminator region, it falls off & transcription stops

RNA exits the Nucleus

•  m/t/rRNA exits the nucleus through a nuclear pore in the nuclear envelope –  Nuclear envelope is a double membrane of 2 lipid bilayers –  Nuclear envelope is continuous with rough endoplasmic reticulum

•  The nucleus contains chromatin, RNA, proteins •  The Nucleolus is the part of DNA that codes for ribosomes

•  Cytoplasm = Everything between the nucleus & the plasma membrane: Cytosol, Organelles & Cytoskeleton

mRNA leaves the Nucleus & enters Cytoplasm

The Cytoplasm consists of:

Cytosol •  75-90% water •  & dissolved substances:

–  ions –  glucose –  amino acids –  fatty acids –  proteins –  lipids –  ATP –  waste products

Organelles •  Centrosome •  Cilia & flagella •  Ribosomes •  Rough Endoplasmic Reticulum • Smooth E R •  Golgi complex •  Lysosome •  Peroxisome •  Proteosome

•  Mitochondria

Cytoskeleton • Microfilaments • Microtubules • Intermediate Filaments

mRNA enters a Ribosome

Ribosomes can be: 1.  FREE - In the cytosol 2.  Attached onto the Rough Endoplasmic Reticulum giving it its“rough”

look 3.  or in the mitochondria

TRANSLATION: RNA codes for PROTEIN

•  mRNA binds to a ribosome •  One amino acid is attached to each tRNA (transfer RNA) •  Each tRNA anticodon matches an mRNA codon •  Amino acids bind together to form an elongating peptide chain

mRNA Codons & tRNA Anticodons

•  A Codon is a set of 3 nucleotides on the mRNA. •  The An“t”icodon is a set of 3 nucleotides on “t”RNA. •  Each codon sequence correlates to a specific amino acid.

Review: from DNA to Cytosolic protein

Transmembrane vs Secretory proteins •  a signal sequence on the amino acid

chain complexes with Signal Recognition Particle (SRP).

•  Together, they guide the ribosome towards the ER.

•  SRP Receptors on the ER, bind the SRP & remove it so that the signal sequence can enter a Translocation channel.

•  Secretory proteins will cross the RER membrane completely to enter the lumen of the RER

•  Transmembrane proteins will

cross the RER membrane partially and remain membrane-bound **

The Golgi Apparatus, or “Post Office”

•  After the RER, proteins move to the golgi apparatus via vesicles.

•  The Golgi apparatus modifies the proteins (eg by adding a sugar for glycoproteins)

•  The Golgi then sorts the proteins headed for the same destination into vesicles. Eg All lysosomal proteins will all be in 1 vesicle.

The Secretory Pathway •  The golgi apparatus

sorts proteins into vesicles.

•  Some vesicles will fuse with the cell membrane.

•  If the proteins were

completely surrounded within the lumen of the vesicle, they will be secreted out of the cell when the vesicle fuses.

Protein moves from RER to Golgi Apparatus

•  Protein modification & sorting •  3 possible places for a RER / Golgi protein to end up:

1.  Membrane Vesicle: As a plasma transmembrane protein 2.  Secretory Vesicle: Secreted out of the cell 3.  Transport Vesicle: Intracellular destination eg lysosome

OTHER ORGANELLES

Smooth ER – Fats & Ca •  The Smooth Endoplasmic

Reticulum has no ribosomes

•  Synthesizes fatty acids & steroids (like estrogen, testosterone)

•  Detoxifies lipid-soluble drugs, pesticides, alcohol,

•  Helps release glucose into blood (cleaves P from G6P)

•  In muscle cells, it stores & releases Ca2+

Lysosomes digest

•  Contains the cell’s digestive enzymes –  Autophagy - breaks down its own damaged organelles –  Phagocytosis - digests external substances like bacteria –  Autolysis - destroys the entire cell that contains the lysosome

•  Enzymes only work at extremely acidic pH (5) –  Proton transporter imports H+ to keep pH low inside

Proteosomes

•  Barrel-shaped organelles that degrade cytosolic proteins, coated with ubiquitin, into peptides.

•  Proteins targeted for degradation may be non-functional, misfolded or…

•  Contain oxidases - enzymes that oxidize organic substances like fatty acids, amino acids & toxic substances like alcohol

•  Numerous in liver cells where toxic substances accumulate for detoxification.

•  By-product of oxidation is hydrogen peroxide, H2O2 (toxic) •  Contain catalase enzyme to degrade H2O2

Peroxisome

THE CYTOSKELETON

A Cell’s CYTOSKELETON •  The cytoskeleton

organizes and moves components of the cell.

•  It is made up of: 1.  ACTIN

MICROFILAMENTS 2.  INTERMEDIATE

FILAMENTS 3.  MICROTUBULES

ACTIN MICROFILAMENTS •  Made of Actin & Myosin Proteins

1.  Responsible for Cell SHAPE –  Forms nonmotile Microvilli –  Creates cell polarity ie Apical vs

basolateral surfaces

2.  Enables Cell MOVEMENT –  Muscle contraction –  Cell locomotion

3.  Requires ATP to assemble

4.  The associated motor molecule is Myosin

Microfilaments & cell movement •  Myosin is the motor

molecule that moves the actin

•  Cell movement is a result of actin microfilaments extending forward & pushing the cell in that direction

MICROTUBULES & the Centrosome

•  Emanate from centrioles within the centrosome –  Minus (-) end is anchored at centriole –  Plus (+) end grows

•  Requires GTP to assemble •  Motor proteins: Kinesin & Dynein MOVE VESICLES along the microtubule in

opposite directions (VESICULAR TRANSPORT) •  Align & pull apart chromosomes during Mitosis •  Make up cilia & flagella

Cytoskeleton Assembly & Disassembly

•  Microfilaments are made of ACTIN –  Myosin is the

motor molecule

•  MICROTUBULES –  Kinesin moves

things towards (+) end

–  Dynein moves things towards (-) end (at the centriole)

INTERMEDIATE FILAMENTS

•  Scaffolding/Stability –  Eg Nuclear lamina

•  Not Dynamic •  Cell-type specific

–  Eg keratin

THE MITOCHONDRIA Krebs Cycle, Electron Transport Chain and ATP production

Mitochondrial Energy Production

•  Fatty acids, amino acids and sugars enter the Citric Acid Cycle within the mitochondria, to produce NADH, a source of electrons and H+ ions. and The electrons enter the Electron Transport Chain while the H+ ions power oxidative phosphorylation by ATP synthase complex to make ATP.

The Electron Transport Chain

•  H+ ions from NADH are pumped into, and collect in the mitochondrial intermembrane space.

•  The H+ concentration gradient is used as 2° active transport energy source to turn ATP synthase which makes ATP

•  H+ entering the mitochondrial matrix attaches to O2 to make H2O

Other mitochondrial functions

1.  Steroid synthesis (pregnenolone, cortisol, aldosterone) 2.  Triggers Apoptosis (cell death)

Back to the Beginning •  Nucleus - Trasncription of DNA to

mRNA which goes out nuclear pores of nuclear envelope

•  Free ribosome - mRNA translation for cytosolic protein synthesis

•  RER - studded with ribosomes. mRNA Translation & Translocation for secretory or transmembrane proteins.

•  Golgi Apparatus - modifies proteins & tags for destination, ↓apoptosis

•  Lysosomes - acidic enzymes •  Centriole - microtubules attach,

mitosis (cell division), vesicle shuttle

•  Cytoskeleton- actin microfilaments, microtubules, Intermediate filament

•  Mitochondria - ATP generation from FA oxidation,protein, carb. cholesterol→ steroids, ↑apoptosis

•  SER - lipid & steroid synthesis/metab, receptor attachment, G6P, enzyme storage/prod, carb metab, Ca regulation

•  Peroxisome - oxidative enzymes, detoxes,

THE CELL CYCLE, APOPTOSIS, AND CANCER

Cell division & Cell death

Cells have 3 possible states of existence:

1.  Remain alive and functional without dividing (G0)

2.  Grow & Divide = The Cell Cycle •  Interphase (G1, S, G2) •  Mitosis

•  Nuclear division: Prophase, Metaphase, Anaphase, Telophase •  Cytokinesis: cytoplasmic division

3.  Die (Apoptosis)

The Cell Cycle

•  Consists of 2 major periods: 1.  Interphase: the cell is replicating itself but not dividing 2.  Mitotic phase: the nucleus is dividing

•  Is the period from cell reproduction to the next reproduction

Interphase: (growth &

replication) G1, S, G2

The majority of a cell’s lifespan is spent in Interphase: •  G1 - normal cell functions, duplication of organelles & cytosol components •  S - DNA replicates •  G2 (Gap2) - centrosome duplication completes.

S phase of Interphase:

DNA replication

•  DNA replicates during S (synthesis) phase.

•  DNA strands separate and new DNA is synthesized along each strand

Mitotic Phase (Division)

•  Mitotic phase: a cell’s nucleus and cytoplasm are dividing.

•  Includes: –  Prophase –  Metaphase –  Anaphase –  Telophase

23 Pairs of Chromosomes

•  Everyone has 23 homologous pairs of chromosomes with with unique banding patterns.

•  One member in each pair is inherited from each parent

Mitosis •  Prophase:

chromosomes are visible, nucleus disappears

•  Metaphase: chromosomes align

•  Anaphase: chromosomes split

•  Telophase: chromosomes uncoil, 2 nuclei form

Cell Cycle – Interphase & Mitotic Cell Division

Cell division: Mitosis vs Meiosis •  There are 2 major kinds of

cells - somatic cells and germ cells

•  Somatic Cell Division ie Mitosis produces 2 identical diploid daughter cells for: –  Healing: replaces dead or

injured cells –  Growth: adds new cells

•  Reproductive Cell Division ie Meiosis produces haploid gametes: –  sperm or oocytes

Turning on cell division

•  CDK’s – Cyclin Dependent protein Kinases will turn on G1, then turn it off, and continue an orderly progression through S, G2, etc

•  Cyclins - turn CDKs on & off

Apoptosis vs. Necrosis

•  Apoptosis - Regulated, genetically programmed cell death (suicide) that does not produce inflammation. Cell is destroyed from within, shrinks & is engulfed by phagocytes.

•  Necrosis - pathological cell death resulting in cell swelling, bursting, spilling contents & inflammation

APOPTOSIS

CANCER

•  Disease state characterized by uncontrolled, or abnormal cell division = CANCER

•  excess tissue resulting from uncontrolled cellular division = TUMOR or NEOPLASM

•  A cancerous neoplasm is called a malignant tumor. Most malignant tumors spread to other parts of the body, or, metastasize.

Proto-oncogenes & Oncogenes

•  Genes are sections of DNA that code for proteins

•  Proto-oncogenes are normal genes that code for proteins that tend to deal with growth or cell division, such as growth factors

•  If these proto-oncogenes should mutate, they become oncogenes and cell division becomes uncontrolled

•  Tumor suppressor genes are genes that code for proteins that stop cell division, or induce apoptosis eg BRCA.

•  Loss of these genes lead to uncontrolled cell division.

Tumor Suppressor

Genes