anatomy and physiology 1

Organization of Cells and Beyond

The Bigge

r Pictur

e

Where do the atoms

and molecules

that we have talked about fit into

the bigger picture?

The Basic Unit of Life is the CellThe Basic Unit of Life is the Cell

Endoplasmic reticulum

Ribosome

Golgi

Lysosome

Plasma membrane

Energy production

Synthesis of proteins

Maintain intracellular environment

Transport across the membrane

Mitosis (DNA replication)

Recycling old cellular components

Mitochondria

NucleusChromosomes

Membrane proteins

Organelles are made from Organelles are made from macromoleculesmacromoleculesStructural components

– Proteins

– Glycolipids

Information/communication

– DNA

– Proteins

Energy sources

– Carbohydrates

– Lipids

– ATP

Carbohydrates are used for energy and for macromolecules

Amino acids make proteins

Lipids make plasma and

organelle membranes

Plasma Membrane: separates the intracellular environment from the extracellular (interstitial) fluid

Plasma Membrane: phospholipid bilayer

Phospholipid

Phospholipid layer

Phospholipid bilayer

Extracellular fluid (ECF): includes plasma and interstitial fluid

Extracellular matrix: jellylike nonliving mesh containing proteins and carbohydrates secreted by cells. Self organizes into a mesh (varies from soft to rock hard) that glues the body together.

Intracellular environment: also water based environment with salts, sugars, amino acids, proteins, membrane bound organelles

Proteins Proteins

• 3D structure of protein determines its function. Disturb shape and loose function

• All proteins are made from a mixture of the 20 amino acids. DNA sequence of genes codes for amino acid sequence

• Each amino acid has chemical personality which influences the way the protein folds

• Some amino acids are polar while others are hydrophobic. The hydrophobic amino acid are found in transmembrane sections of proteins

Transport

Receptors

Intercellular joining

Cell-cell recognition

Attachment

Enzymatic activity

Crossing the membrane: what does semi-permeable mean?

Simple diffusion Carrier mediated

Channel mediated Osmosis

The chemical properties of a molecule determine how that molecules moves across the plasma membrane.

May be active or passive

May be active or passive

• Monosaccharides are building blocks. Only form that crosses the membrane

– 6 carbon (hexoses) such as glucose

– 5 carbon (pentoses) such as ribose

• Disaccharides are food made of two monosaccharides

– sucrose, lactose and maltoses

• Polysaccharides large carbohydrate storage molecules

– Glycogen, cellulose

Polar molecules cross via facilitated diffusion or active transportCarbohydratesCarbohydrates

Na+ (11p)

+

Cl- (17P

)

-

Ions cross via ion channel proteins

Concentrations do NOT have to be equal on both sides of the membrane.

In many cases life depends on concentrations be different across membranes!

• Think about the generation of electricity by hydroelectric power

– Membranes can act as dams preventing molecules from crossing.

– When the concentration is higher on one side of the membrane there is drive toward equilibrium (same concentration on each side)

– When molecules move from higher concentration to lower concentration energy can be captured

– Pushing molecules up there concentration gradient requires energy input

– Water in biological systems freely moves through membranes and never accumulates in a concentration gradient

– Water is at the mercy of other concentration gradients and will move to achieve equilibrium

Concentrations inside the cells are NOT always equal to concentrations outside for many solutes.

Higher concentration Na+

Lower concentration Na+

Energy is needed to

move across

membrane

Outside cell

Inside cell

Higher concentration Na+

Lower concentration Na+

No energy needed to

move across

membrane

Outside cell

Inside cell

Lower concentration K+

Higher concentration K+

No energy needed to

move across

membrane

Lower concentration K+

Higher concentration K+

Energy is needed to

move across

membrane

• Water freely diffuses across membranes (through aquaporins)

• The direction of water movement is determined by the relative solute concentration inside and outside the cell

• Water always moves down its concentration gradient

Water

Higher concentration of solutes (hypertonic)

Lower concentration solutes

Cell will dehydrate

Lower concentration of solutes (Hypotonic)

Higher concentration solutes

Cell will swell

Outside cell

Inside cell

Selective permeability of membranes is necessary for life

• Selective permeability is a characteristic of healthy, intact cells. When a cell (or its plasma membrane) is severely damaged, the membrane becomes permeable to virtually everything, and substances flow into and out of the cell freely. This phenomenon is evident when someone has been severely burned. Precious fluids, proteins, and ions "weep" from the dead and damaged cells

• Selective permeability maintains concentrations of molecules on both sides of the membrane

• The cells in our body have both a plasma membrane surrounding the cell and a series of membrane bound internal structures called organelles that house the everyday functions of the cell. Internal membranes create microenvironments needed for reactions inside the cell.

So what do cells do all day?

• Maintain concentration gradients

• Metabolism to generate energy

• Respond to chemical messages in the blood

• Make useful proteins

• Digest debris in the cytoplasm

• Transport stuff around within the cell

• Divide into 2 daughters cells

• Organize into structural units called tissues









Mitochondria

Hormone Receptors/Second Messengers

Receptors• Maintain concentration

gradients








Ribosomes/Endoplasmic Reticulum/Golgi









Making of macromolecules

• Macromolecules are polymers of smaller molecules• ~ 30 small precursors are combined into a diversity of macromolecules• Biosynthesis is highly regulated• Proteins are the doers in the cell.• All information in DNA is about making proteins • Proteins are not made directly from DNA, but rather from RNA (transcription

is making RNA from DNA; translation is making proteins from RNA)• After translation, proteins may be cut, glycosylated (sugars added), and

packaged

Macromolecule Precursors

Polysaccharides (e.g., glycogen starch)

Monosaccharides (e.g., glucose)

Proteins Amino acids (20 different ones)

Nucleic Acids (DNA, RNA) Nucleotides (4 different ones)

Peptidoglycan cell wallAmino acids and monosaccharides

tRNAs bring in amino acids

AUG CUG GGG GUA CUC GCG CUA CCC GGG UAA

mRNA

tRNARibosom

eMet

Leu

GAC


mRNA

tRNARibosom

eMet

Leu

GACUAC

UAC

tRNAs bring in amino acids

Pro

GGG

MetLeu

GlyVal

Leu AlaLeu

GAU


mRNA

tRNA with

amino acidGrowing peptide

chain (peptidyl transferase makes peptide

bonds)Ribosom

e

CGC

Empty tRNA

Stop signal

Aminoacyl-tRNA transferase attaches amino acid to its tRNA

Lysosomes









Glycogen and certain lipids in the brain are degraded by lysosomes at a relatively constant rate. In Tay-Sachs disease, an inherited condition seen mostly in Jews from Central Europe, the lysosomes lack an enzyme needed to break down a glycolipid abundant in nerve cell membranes. As a result, the nerve cell lysosomes swell with the undigested lipids, which interfere with nervous system functioning. Affected infants typically have doll-like features and pink translucent skin. At 3 to 6 months of age, the first signs of disease appear (listlessness, motor weakness). These progress to mental retardation, seizures, blindness, and ultimately death within 18 months.

Cytoskeleton









Microtubules/Centrioles









Tissues









Cells – the basic structural and functional units of the organismCells specialize in particular jobs, e.g., muscle cells are specialized for contracting

Tissue levelGroups of different cell types cooperate to perform specific functions

Essential Concepts: The Hierarchy of Structural Organization

What does a highly organized body do?

What do cells do? What does the body do?

Maintain concentration gradients

Maintain boundaries with outside

Metabolize nutrients to generate energy

Digest nutrients

Respond to chemical messages in the blood

Respond to changes in the environment

Make useful proteins Grow Digest debris in the cytoplasm Excrete (get rid of wastes)Transport stuff around within the cell

Move relative to external environment and move substances internally

Divide into 2 daughters cells ReproduceOrganize into structural units called tissues

Stay the same while constantly changing (homeostasis)

anatomy and physiology 1

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higher concentration

concentration gradients

concentration gradientwater

hydrophobic amino acid

lower concentration

capturedpushing molecules

sidewhen molecules

protein foldssome amino