Introducing 

Prezi AI.

Your new presentation assistant.

Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.

Loading…
Transcript

Transport in Cells

Passive and active transport

Passive Transport

It involves the movement of material along a concentration gradient (high concentration low concentration)

Because materials are moving down a concentration gradient, it does not require the expenditure of energy (ATP hydrolysis

Passive Transport

There are three main types of passive transport:

  • Simple diffusion – movement of small or lipophilic molecules (e.g. O2, CO2, etc.)
  • Osmosis – movement of water molecules (dependent on solute concentrations)
  • Facilitated diffusion – movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.)

Passive Transport

Simple Diffusion

Is the net movement of molecules from a region of high concentration to a region of low concentration

  • This directional movement along a gradient is passive and will continue until molecules become evenly dispersed (equilibrium)
  • Small and non-polar (lipophilic) molecules will be able to freely diffuse across cell membranes (e.g. O2, CO2, glycerol)

Simple Diffusion

Rate of Diffusion

can be influenced by a number of factors, including:

  • Temperature (affects kinetic energy of particles in solution)
  • Molecular size (larger particles are subjected to greater resistance within a fluid medium)
  • Steepness of gradient (rate of diffusion will be greater with a higher concentration gradient)

Video

Osmosis

is the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)

Osmosis

Universal Solvent

Water is considered the universal solvent – it will associate with, and dissolve, polar or charged molecules (solutes)

Because solutes cannot cross a cell membrane unaided, water will move to equalise the two solutions

At a higher solute concentration there are less free water molecules in solution as water is associated with the solute

Osmosis is essentially the diffusion of free water molecules and hence occurs from regions of low solute concentration

Relationship between Solute Concentration and Levels of Free Water Molecules

Relationship between Solute Concentration and Levels of Fr...

SOLUTIONS

  • Solutions may be loosely categorised as hypertonic, hypotonic or isotonic according to their relative osmolarity
  • Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration gains water)
  • Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration loses water)
  • Solutions that have the same osmolarity are categorised as isotonic (same solute concentration no net water flow)

Osmotic movement

Osmolarity

  • The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
  • Water loss or gain may be determined by weighing the sample before and after bathing in solution
  • Tissue osmolarity may be inferred by identifying the concentration of solution at which there is no weight change (i.e. isotonic)

Osmosis in plants and animals

Uncontrolled osmosis will have negative effects with regards to cell viability:

ANIMALS

  • In hypertonic solutions, water will leave the cell causing it to shrivel (crenation)
  • In hypotonic solutions, water will enter the cell causing it to swell and potentially burst (lysis)

PLANTS

  • In plant tissues, the effects of uncontrolled osmosis are moderated by the presence of an inflexible cell walll
  • In hypertonic solutions, the cytoplasm will shrink (plasmolysis) but the cell wall will maintain a structured shape
  • In hypotonic solutions, the cytoplasm will expand but be unable to rupture within the constraints of the cell wall (turgor)

summary

Facilitated diffusion

Is the passive movement of molecules across the cell membrane via a membrane protein

It is utilised by molecules that are unable to freely cross the phospholipid bilayer (e.g. large, polar molecules and ions)

This process is mediated by two distinct types of transport proteins – channel proteins and carrier proteins

Facilitated diffusion

Carrier Proteins

  • Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane
  • Carrier proteins will only bind a specific molecule via an attachment similar to an enzyme-substrate interaction
  • Carrier proteins may move molecules against concentration gradients in the presence of ATP (i.e. are used in active transport)
  • Carrier proteins have a much slower rate of transport than channel proteins (by an order of ~1,000 molecules per second)

Channel Proteins

Integral lipoproteins which contain a pore via which ions may cross from one side of the membrane to the other

Channel proteins are ion-selective and may be gated to regulate the passage of ions in response to certain stimuli

Channel proteins only move molecules along a concentration gradient (i.e. are not used in active transport)

Channel proteins have a much faster rate of transport than carrier proteins

Lets see how they work

Active Transport

It involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)

Because materials are moving against the gradient, it requires the expenditure of energy (e.g. ATP hydrolysis)

There are two main types of active transport

  • Primary (direct) active transport – Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport
  • Secondary (indirect) active transport – Involves coupling the molecule with another moving along an electrochemical gradient

Sodium-Potassium Pump

Active Transport

video

Vesicular Transport

Materials destined for secretion are transported around the cell in membranous containers called vesicles

(TYPE OF ACTIVE TRANSPORT)

Endoplasmic Reticulum

The endoplasmic reticulum is a membranous network that is responsible for synthesising secretory materials

Rough ER is embedded with ribosomes and synthesises proteins destined for extracellular use

Smooth ER is involved in lipid synthesis and also plays a role in carbohydrate metabolism

Materials are transported from the ER when the membrane bulges and then buds to create a vesicle surrounding the material

Golgi Apparatus

The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex

Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face

While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.)

Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome

Golgi Apparatus

Plasma Membrane

Vesicles containing materials destined for extracellular use will be transported to the plasma membrane

The vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid

Materials sorted by the Golgi apparatus may be either:

  • Released immediately into the extracellular fluid (constitutive secretion)
  • Stored within an intracellular vesicle for a delayed release in response to a cellular signal (regulatory secretion)

Plasma Membrane

Vesicular transport

Endo and Exocytosis

EXOCYTOSIS

The process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane

Vesicles (typically derived from the Golgi) fuse with the plasma membrane, expelling their contents into the extracellular environment

The process of exocytosis adds vesicular phospholipids to the cell membrane, replacing those lost when vesicles are formed via endocytosis

ENDOCYTOSIS

The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane

An invagination of the membrane forms a flask-like depression which envelopes the extracellular material

The invagination is then sealed off to form an intracellular vesicle containing the material

ENDOCYTOSIS

Main Types

Phagocytosis – The process by which solid substances are ingested (usually to be transported to the lysosome)

Pinocytosis – The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)

Main Types

Learn more about creating dynamic, engaging presentations with Prezi