Week 2 Lecture 4 Cell Physiology Flashcards
Active transport
Moving solutes against there concentration gradient
Requires energy
-primary active transport- hydrolysis of ATP
-secondary active transport - energy in an ion concentration gradient
Primary active transport
Energy from ATP hydrolysis
Change the shape of a carrier protein
Pump the solute across the membrane against its concentration gradient
40% of the ATP in a cell is generated on primary active transport.
Sodium-potassium pump
• Move Na+ into the extracellular fluid
• Pump against 3 Na+ gradient
• Move 2 K+ into the cytosol
• Pump against K+ gradient
• Leak back down their electrochemical gradients
Open on inside so sodium can bind
Na+- K+- ATPase
Secondary active transport
-Uses the energy stored in a Na+ or H+ concentration gradient
• Move solutes against their concentration gradient
• Indirect use of ATP
Ions in high concentration have high kinetic energy
N
• Steep Na+ concentration gradient (sodium-potassium pump)
• Na+ ions have potential energy
• Na+ ions leak back in
—Stored energy converted to kinetic energy
— Moves substances against their concentration gradient
Secondary active transport pt 2
• Carrier protein binds Na+ and other substance simultaneously
• Protein changes shape so both substances cross the membrane simultaneously
SYMPORTERS
Move substances in same direction
Carrier proteins, specific binding sites, a comfermational change in shape to allow transport
ANTIPORTERS
Move substances in opposite direction
Clinical relevance
• Digitalis [medication] for heart failure
• Slows the sodium-potassium pump, not at steep concentration gradient
• Na+ accumulates in the heart muscle – decreased concentration gradient
• Na+ - Ca2+ antiporters slow and calcium accumulates
• Increases force of muscle contraction
Vesicle transport
• Endocytosis
—Movement into a cell
—Vesicle from plasma membrane- pull it into cell
• Exocytosis
—Movement out of a cell
—Intracellular vesicles fuse with plasma membrane
Release something out of the cell
• both Active process requiring ATP
Endocytosis
• Receptor-mediated endocytosis
• Highly selective
• Specific ligands
• E.g. LDLs, transferrin, some vitamins
• Old cells, viruses, bacteria
• Phagocytes (macrophages or neutrophils)
Phagocytosis
• Old cells, viruses, bacteria
• Phagocytes (macrophages or neutrophils)
Bulk-phase endocytosis
• Pinocytosis
• Take up of extracellular fluid
Exocytosis
• Release material from a cell
• Secretory cells – enzymes,
hormones, mucus
• Nerve cells – neurotransmitters
• Waste
• Intracellular secretory vesicles
Transcytosis
• Transport molecules across a cell
• Endocytosis and exocytosis
Eg GI tract for absorbotion
Cytoplasm pt1
Cytoplasm – cell contents between membrane and nucleus
• Cytosol
—Intracellular fluid
—55% of cell volume
—75 – 90% water with dissolved/suspended contents
• Organelles
—Specialised structures
—Characteristic shapes
—Specific functions in growth, maintenance and reproduction
Cytoplasm pt 2
• Cytoskeleton
Hold organelles where they need to be
• Protein filament network
• Cell shape and organisation
• Movement
• Microfilaments =smallest
• Intermediate filaments= middle
• Microtubules=largest
Cytoplasm pt 3
• Microfilaments edge of the cell
• Actin and myosin
• Most prevalent at the cell edge
• Movement and mechanical support
Micro Lili = increase SA
• Intermediate filaments, hold different organelles in shape
Internal structure
• Thicker than microfilaments
• Stabilise position of organelles
• Cell to cell attachment keeping cells together
Cytoplasm pt 4
• Microtubules
• Largest cytoskeleton components
• Unbranched hollow tubes
• Tubulin
• Cell shape and organelle movement
Hold entire cell shape
Much stronger
Ribosomes
• Sites of protein synthesis
• High content of ribonucleic acid
• Two subunits large and small subunits
• Attached to the endoplasmic reticulum
Endoplasmic reticulum
• Network of membranes as flattened sacs
Increase sa = more ribosomes = efficiency
• Rough ER
• Ribosomes embedded
• Secretory, membrane and organellar proteins
• Glycoproteins and phospholipids
Smooth ER
• Enzymes
• Fatty acids and steroid synthesis
• Detoxify drugs
• Repeated exposure to drug leads to tolerance
Golgi complex
-3 to 20 saccules
• Modify, sort and package proteins
• Entry face – receives & modifies proteins from RER
• Intermediate saccules add carbohydrates or lipids
• Exit face – further modification, sorts and packages for destination
Lysosomes
• Digestive & hydrolytic enzymes
• Digest substances that enter via endocytosis
Old organelles or entire cells
• Autophagy
• Autolysis
• Extracellular digestion
• Acidic pH 5
Peroxisomes
• Contain oxidases (remove H atoms)
• breaking down Amino acids, fatty acids into component parts
• Toxic substances e.g., alcohol
