week 2 (lecture 3&4)

• minimal requirements for a cell

  • plasma membrane: selective barrier between the inside and outside of cell (controls what comes in & what goes out)
  • cytoplasm: water soluble area where all chemical rxn that make up the cell happen protected by plasma membrane
  • DNA: encodes the instructions that tells the cell how to make itself
  • ribosomes: translates the instructions from DNA into proteins

  
• what limits cell size

  • lower limit: needs enough volume to carry the DNA and the basic components to express those genes
  • upper limit: enough surface area - volume ratio to satisfy diffusive entry of O2, nutrients and removal of wastes. (as cell gets bigger, volume increases relative to surface area, this restricts cell's ability to take in and expel nutrients & O2)
• Plasma membrane

  • is a phospholipid bilayer (2 phospholipid layers)
  • what can pass: small molecules, uncharged stuff, O2, CO2
  • hydrophilic head: exposed to outside and inside of cell which are both water soluble
  • hydrophobic tail: creates a hydrophobic core (non-polar)

  A) phosphate

  B) glycerol

  C) saturated

  D) unsaturated

  
• Fluid-mosaic model of plasma membrane

  • cell membranes are a mosaic of lipids and proteins
  • mosaic - pattern made of small irregular pieces
  • integral proteins: permanently bound within membrane due to a non-polar region which is attracted to the hydrophobic core.
  • peripheral proteins: not embedded into the membrane due to lack of hydrophobic region, usually bound to something else that is binded to membrane (eg. integral membrane protein)

  A) peripheral

  B) transmembrane

  C) membrane

  
• phospholipids - the glue of the membrane

  • phosphatidylcholine: most common phospholipid
  • glycolipid: assists with signal transduction through cell membrane
  • sterol: assits regulating fluidity of membrane (ie. cholesterol is a sterol in animals membranes). At high temps, sterol reduces fluidity, at low temps, sterol reduces rigidity

  A) choline

  B) double bond

  C) glycolipid

  D) sterol

  
• types of membrane functions

  A) ATP

  B) transduction

  C) extracellular

  D) membranes

  E) mitochondria

  F) communication

  
• Diffusion

  • Movement of solutes from regions with higher concentration into regions with lower concentration
  • Net diffusion stops when an equilibrium concentration is reached throughout

  A) equilibrium

  
• Diffusion (example - refer to diagram)

  1. low conc left side + high conc right side
  2. the seletive membrane allows water to pass but not sugar
  3. since there is less water on right side (bc of more sugar) the water travels to right side
  4. this is called osmosis - water moves from area of lower conc to higher conc to have similar concentrations

  link to cells: if there's a high solute conc inside cell (that can't escape) and low conc outside cell (that can't come in), water would rush into the cell to reach EQ and explode it. Hence why proteins are needed to transport solutes and water

  A) osmosis

  
• Transport proteins

  • Allow large or charged molecules to be transport across membranes
  • electrochemical gradient: think of as a ball rolling from high part of hill to lower part. Just as equilibrium is reached when solute moves down the electrochemical gradient

  A) extracellular

  B) electrochemial

  
• Passive transport - Facilitated diffusion

  • Molecules move down a concentration gradient via transporter proteins (eg. channel proteins or carrier proteins)
  • channel protein: has an OPEN hydrophilic space
  • carrier protein: have very specific part of protein that recognises a specific solute and binds it, then transports it across membrane
  • simple diffusion: passing straight through lipid bilayer is very slow, dependent on size of molecule and less control

  A) simple diffusion

  B) channel

  C) carrier

  D) passive

  
• Active transport

  • solute transporting AGAINST the electrochemical gradient
  • analogy: for a ball to go up a hill, energy is required. For molecules to transport against the gradient, energy, in the form of ATP is used.

  A) energy

  
• Electrogenic pumps

  1. Proton pump uses ATP to push cations outside of the cell
  2. When enough protons are pushed out, the pump has generated an electrochemical gradient which is a new store of potential energy used for transporting back across membrane and other processes

  A) pump

  B) ATP

  C) extracellular

  
• diagram

  A) intermembrane space

  B) mitochondrial matrix

  C) internal rod

  D) knob

  E) stator

  F) rotor

  G) inner

  H) shape

  
• ATP production - mitochondria

  1. there's a high gradient of H+ ions in intermembrane space, so to reach EQ, there's pressure to move down electrochemical gradient
  2. since membrane is impermeable, H+ enters a channel of the stator, binding to the rotor (ATP synthase)
  3. after 1 rotation, H+ exits through another channel into mitochondrial matrix
  4. spinning of rotor causes internal rod to spin. The rod is attached to a knob which doesn't move due to stator.
  5. turning of the rod activates catalytic sites in knob, producing ATP (ADP + P)

  
• cotransport - transport across the membrane

  • uniport: proteins transporting one molecule at a time
  • symports: proteins transporting 2 molecules in same direction
  • antiport: protein transporting 2 molecules in different direction

  A) uniport

  B) symport

  C) antiport

  
• cotransporter example - Na+/K+ pump

  • Na+ is toxic to cell in high concentrations
  • K+ is the major intracellular cation for cells (pro & eu)
  • this constant process enables cell to maintain, via contransport, equilibrium conc. of Na+ & K+

  1. when 3 Na+ is binded to the protein, ATP powers the transport of the ions outside, causing CONFORMATIONAL shape change to the protein (due to P)
  2. this shape change allows 2 K+ to bind to the protein (releasing P) which causes another conformational change to its original shape, also releasing K+ inside the cell

  A) extracellular

  B) conformational

  C) high

  D) low

  
• cotransporter example - sucrose/H+

  • the cotransporter only move H+ if sucrose is bound too

  A) pump

  B) diffusion

  C) ATP

  
• prokaryotes vs eukaryotes

  A) circular

  B) linear

  C) proteins

  D) binary

  E) mitosis & meiosis

  F) organelles

  
• endosymbiotic theory

  • explains the origin of eukaryotic cells and their organelles, highlighting the importance of symbiotic relationships
  • modern eukaryotic cell = prokaryotic cell + prokaryotic cell

  A) prokaryote

  
• endosymbionts - mitochondria

  • function: production of ATP (hence, powerhouse of cell)
  • different cells have different numbers of mitochondria, depending on their energy requirements
  • the mitochondrial matrix increases surface area, increasing space for reactions to generate ATP
  • outer membrane is eukaryotic-like & inner membrane is prokaryotic-like

  A) DNA

  B) matrix

  C) ribosomes

  
• endosymbionts - chloroplasts

  • function: carry out photosynthesis (light energy -> chemical)
  • found in plant cells, green coloured due to green pigment chlorophyll
  • outer & inner membrane: regulate the passage of molecules in and out of chloroplast
  • stroma: gel-like matrix that fills the interior, contains enzymes necessary for the Calvin cycle (how it turns CO2 to sugar)
  • thylakoids: when stacked up, called grana, contain chlorophyll and other pigments that capture light energy during the light-dependent reactions of photosynthesis.

  A) grana

  B) stroma

  C) thylakoid

  
• endosymbionts - nucleus

  • function: control center for cellular activities
  • contains all the genetic material except for mitochondria & chloroplasts (have their own DNA)
  • nuclear envelope: double membrane surrounding nucleus.
  • nuclear pores: scattered across the envelope, allowing passage of molecules between nucleus & cytoplasm
  • chromatin: mixture of DNA and proteins that form chromosomes (condenses in interphase)
  • nucleolus: centre of the nucleus, gathers ribosomal RNA (rRna) to form ribosomes

  A) pores

  B) chromatin

  C) envelope

  D) nucleolus

  
• endosymbionts - ribosomes

  • function: translates the genetic info mRNA into a specific sequence of amino acids, determining the primary structure of the protein.

  1. production of mRNA in nucleus from DNA
  2. mRNA moves through the nuclear pores into cytoplasm
  3. ribosome reads the mRNA and produces the primary structure of protein

  A) ribosome

  B) mRNA

  
• endoplasmic reticulum (ER)

  • endoplasmic: inside the cell. reticulum: long winded skinny object
  • rough ER (RER): has ribosomes on surface, gives a "rough" look, they're responsible for protein synthesis/storage (mRNA->polypeptide->glycoprotein)
  • smooth ER (SER): no ribosomes on surface, gives "smooth" look, invovled in lipid (eg. fatty acid) & steroid (eg. cholestrol) creation/storage

  
• Endomembranes

  • A system of membrane-bound organelles that can form physical links to exchange components (ie. linked organelles can transfer proteins, lipids & other molecules)
  • basically a group of organelles that modify, pack, and transport lipids and proteins in the cell

  
• Golgi apparatus - the postal service

  • function: sorting, modification, and packaging of proteins & lipids from the ER to their final location (inside or outside cell)
  • cis-golgi: facing the ER, entry point for proteins and lipids
  • medial-golgi: modification & processing proteins/lipids from the ER
  • trans-golgi: not facing ER. Sorting, packaging, and distribution of proteins and lipids to their final destination through VESICLES
  • disconnected from endomembrane system

  A) vesicles

  B) proteins

  C) cis

  D) trans

  E) secretion

  
• stains

  A) DNA

  B) chromatin

  C) RNA

  
• Golgi continued

  • most proteins are packed in vesicles which form lysosomes
  • some proteins are secreted from cell
  • some proteins join the cell membrane
  • some proteins go to other organelles (eg. ER, mitochondria)
  • the destination of the protein depends on the FUNCTION of it

  A) cisternae

  B) lumen

  C) vesicle

  D) cis

  E) trans

  
• Lysosomes - recycling/digestive centre

  • function: they're a type of vesicle, full of digestive enzymes to breakdown macromolecules
  • Phagocytosis: a process where cells engulf "food" from outside (eg. Macrophages are white blood cells that engulf bacteria)
  • Autophagy: a process where damaged organelles are broken down for recycling to make new organelles (eg. liver recycles half its macromolecules per week)

  A) phagocytosis

  B) autophagy

  C) lysosome

  
• why are eukaryotes so special?

  • due to compartmentalization, allowing specific functions to be carried out in a secured manner
  • eg. if lysosomes didn't have a membrane, the enzymes would digest the cell itself
• Vacuoles

  • function: provides structural support & stores a lot of things (eg. food, waste & water)
  • storage function: stores nutrients & water in case the cell needs energy for growth
  • structure function: central vacuole maintains turgor pressure (ie. internal pressure -> press against cell wall)

  
• Cytoskeleton - "maintains cell shape" in different ways

  • Microfilaments: It maintains or changes cell SHAPE. Has narrow fibres containing actin (a protein) involved in cell movement.
  • Intermediate filaments: It maintains the cell shape. Formed from different proteins. (eg. prevents skin cells from tearing)
  • Microtubules: It maintains cell shape, helps move organelles. Made from Tubulin subunits (α & β). (eg. movement of vesicle secretion, form spindle fibres invovled in movement of chromosomes in mitosis & meiosis)
• cytoskeleton mindmap

  A) microtubules

  B) intermediate filaments

  C) microfilaments

  D) tubulin

  E) actin

  F) contraction

  G) cytokinesis

  
• Microtubules

  • formed by sets of tubulin dimers
  • dimer = 2 sets of proteins which go together (ie. α & β)
  • α tubulin can grow quickly in length, whereas β is not as fast.
  • fast side = (+), slow side = (-)
  • the (-) side starts at the microtubule organising centre/central zone, then microtubules grow out

  
• 2nd cytoskeleton function - motility

  • motility involves cell movement, shape change and transport of materials within the cell
  • flagella: longer and fewer in number, made for moving the cell (eg. sperm cells swimming through fluids)
  • cilia: shorter and more in number, made for moving the cell and fluids around it (eg. respiratory cilia moves mucus trapped in airway)
  • axoneme = bundle of microtubules arranged in 9+2 pattern (similar in cilia & flagella)
• motility diagram

  A) cilia

  B) flagella

  C) dynein