Cellular Transport and Processes

Unit 4Obj. 1.2.1, 4.2.1, 4.2.2

The Cell Membrane

The gateway to the cell

Cell Membrane

• Flexible• Allows unicellular organisms to move

Functions of the Cell Membrane

• Protection• Regulates what comes in and out• Allows cell recognition• Anchoring sites for cytoskeleton• Attachment sites for enzymes• Binds cells together at junctions• Contains cytoplasm

Structure and Components of Cell Membrane

• Phospholipid = phosphate head (hydrophilic) and lipid tails (hydrophobic)

• Bilayer = two layers• Studded with proteins (peripheral = partially

through and integral = all the way through) and carbohydrates

Phospholipids

• Contains two fatty acid chains that are non-polar (tail) and a polar head made of -PO4

(phosphate)

Selective Permeability

• Hydrophobic and hydrophilic• Polar and non-polar• Allows membrane to “choose” what comes

across and maintain homeostasis• Hydrophobic molecules (can dissolve in lipids)

pass easily, hydrophilic molecules(can dissolve in water) do not

Semi-permeable membrane

• Hydrophobic molecules can pass through freely even if they are large

• Hydrophilic molecules can only pass through freely if they are very small and can “slip through the cracks”

• Examples: CO2, O2, H2O

Homeostasis

• Balanced internal condition of cells• Also called equilibrium• Maintained by plasma membrane controlling

what enters and leaves the cell

TYPES OF TRANSPORT

Simple Diffusion

• Requires no energy passive transport• Molecules have a natural kinetic energy• Molecules move from an area of high

concentration to an area of low concentration

Diffusion in Liquids

Diffusion Through a Membrane

• Solute moves down the concentration gradient from high to low

Osmosis

• Diffusion of water across a membrane water is so special, it gets its very own transport!

• Moves from high water potential to low water potential

Osmosis

High water potential, Low solute concentration

Low water potential, High solute concentration

Aquaporins

• Special channels for water to pass through during osmosis

Comparing Solutions

• Isotonic = when the concentration of two solutions is the same

• Hypotonic = when comparing two solutions, the solution with the lesser concentration of solutes

• Hypertonic = when comparing two solutions, the solution with the greater concentration of solutes

Cell in Isotonic Solution

CELL

10% NaCL90% H2O

10% NaCL90% H2O

What is the direction of water movement?

The cell is at _______________. equilibrium

ENVIRONMENT

NO NET MOVEMENT

Cell in Hypotonic Solution

CELL

10% NaCL90% H2O

20% NaCL80% H2O

What is the direction of water movement?

Cell in Hypertonic Solution

CELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENT

Cells in Solutions

What can happen to a cell in different solutions?

• Cytolysis = the cell bursts from water rushing in and making it swell up, occurs in hypotonic solutions

• Plasmolysis = the cell shrivels up from water rushing out, occurs in hypertonic solutions

isotonic hypotonic hypertonic

Cytolysis and Plasmolysis

Osmosis in Red Blood Cells

Isotonic Hypotonic Hypertonic

hypotonic hypertonic isotonic

hypertonic isotonic hypotonic

Facilitated Diffusion

• Does not require energy passive transport• Needs some help from transport proteins they

allow the molecules through• Molecules move from high to low concentrations• Channel proteins = embedded in the cell

membrane and have pore for materials to cross• Carrier proteins = can change shape to move

material from one side to the other

Channel Proteins

Carrier Proteins

Active Transport

• Requires energy or ATP to occur• Moves materials from low to high

concentrations = against the concentration gradient

Other forms of cell transport

• Exocytosis = cell releases large amount of material

• Endocytosis = cell takes in a large amount of material by folding it in the cell membrane

• Pinocytosis = cell takes in liquid, “cell drinking”• Phagocytosis = extensions of cytoplasm

surround and engulf large particles and take them into the cell

Exocytosis

Exocytosis

Endocytosis

Pinocytosis

Pinocytosis

Phagocytosis

Photosynthesis

We need energy

• Energy is the ability to do work• Most energy on earth comes from the sun• Heterotrophs get energy by eating other

organisms• Autotrophs make their own food and energy photosynthesis = when they use the sun (light energy) as their energy source

How do we store energy?

• Chemical bonds are formed = energy is stored• Chemical bonds are broken = energy is

released• Adenosine triphosphate (ATP) = main source

of energy for cells, provides power for almost all functions

• Contains adenine, ribose (5-carbon sugar), and 3 phosphate groups

How do we store energy?

• ATP = “charged” battery, stores energy• Energy is released by breaking off the last

phosphate group Adenosine diphosphate (ADP)

• ADP = “dead” battery, energy has been released

How does photosynthesis work?

• Plants use the energy from the sun to convert water and carbon dioxide into oxygen and glucose (sugar)

• Joseph Priestly – discovered that plants make oxygen. He placed a lit candle under a jar and waited until it had consumed all the oxygen. He discovered that if he placed a sprig of mint in the jar and waited a few days, the candle could be lit again, indicating that the plant produced oxygen.

Photosynthesis equation

• 6CO2 + 6H2O light> C6H12O6 + 6O2

• Carbon dioxide + water light> glucose + oxygen

• Carbon dioxide, water, and light must be present for photosynthesis to occur

What kind of light does photosynthesis need to occur?

• Sunlight is “white” light a mixture of different wavelengths of light

• Pigment = light-absorbing molecule• Chlorophyll = main pigment of plants, does

not absorb green light very well gets reflected back to our eyes

Inside a Chloroplast

• Thylakoids = small disc-shaped saclike photosynthetic membranes

• Grana = stacks of thylakoids• Stroma = region outside thylakoid membranes

Electron Carriers

• Electrons gain a great deal of energy when they are excited by the sun require special carriers

• NADP+ (nicotinamide adenine dinucleotide phosphate) = main electron carrier

• NADP+ holds 2 high energy electrons and additional hydrogen ion becomes NADPH

• NADPH carries electrons to chemical reactions elsewhere in the cell

Two Parts of Photosynthesis

• 1. Light-dependent reaction = produces energy from solar power (photons) in the form of ATP and NADPH

• 2. Calvin Cycle or Light Independent Reaction– Also called “carbon fixation” or “C3 Fixation”– Uses energy (ATP and NADPH) from light reaction

to make glucose

Factors affecting photosynthesis

• Temperature• Availability of water• Light intensity

• These factors are different in different areas of the world plants develop special adaptations

Respiration

What is cellular respiration?

• Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.

• Two kinds of respiration:– Aerobic respiration = occurs if oxygen is present– Anaerobic respiration = occurs if oxygen is not

present

Equation

• Cellular respiration:6O2 + C6H12O6 6CO2 + 6H2O + Energy (ATP)

• Recall – Photosynthesis equation: 6CO2 + 6H2O light> 6O2 + C6H12O6

Process

• Cellular respiration happens in a series of steps

• Energy is released slowly, which allows the cell to trap more of it and store it in ATP

Process

• Step 1: Glycolysis• One molecule of glucose (C6H12O6) is broken in half, producing

two molecules of pyruvic acid (C3H6O3)• Uses up 2 molecules of ATP energy “investment”• 4 molecules of ATP are produced net gain of 2 ATP molecules• Occurs in cytoplasm of cell• Does not require oxygen can be part of aerobic or anaerobic

respiration• Electron carrier = NAD+ (without electron pair) NADH (with

electron pair)

Process – Anaerobic respiration

• Step 2: Fermentation• Occurs in cytoplasm of cells• In plants, yeasts, etc. it is called “alcoholic

fermentation”pyruvic acid + NADH alcohol +CO2 + NAD+

• In animal cells and some prokaryotes, it is called “lactic acid fermentation”pyruvic acid + NADH lactic acid + NAD+

• Lactic acid = burning sensation in muscles during exercise

Process – Aerobic respiration

• Step 2: Krebs cycle• Occurs in mitochondria• Pyruvic acid is broken down into carbon dioxide• Produces 2 ATP

Process – Aerobic respiration

• Step 3: Electron transport chain• Occurs in mitochondria• Produces H2O and 34 ATP

Comparing aerobic and anaerobic respiration

Aerobic respiration• Produces 36 ATP• Produces CO2 and H2O• Occurs in mitochondria and

cytoplasm

Anaerobic respiration• Produces 2 ATP• Can produce CO2, lactic

acid, and/or alcohol• Occurs in cytoplasm

Comparing photosynthesis and cellular respiration

Photosynthesis Cellular Respiration

Function Energy capture Energy release

Location Chloroplasts Mitochondria

Reactants CO2 and H2O C6H12O6 and O2

Products C6H12O6 and O2 CO2 and H2O

Equation 6CO2 + 6H2O C6H12O6 + 6O2 C6H12O6 + 6O2 6CO2 + 6H2OEnergy Energy