Cells Flashcards
Cell structure & functions, plasma membrane, cellular transport and the study of cells
What are cells?
basic structure and functional unit of a living organism
What are tissues?
groups of cells with similar structures that work together to perform a function
What are organs?
a structure made up of different tissues within an animal that perform a specific function
What is a system?
a group of organs and tissues related by function e.g. nervous system
What are 6 functions of cells?
- provides support and structure
- aid in reproduction
- transportation of substances
- facilitate growth
- energy production
- specialised functions e.g. nervous system
How many cells are we estimated to have in our bodies?
37.2 billion
What are the two types of cells?
- Prokaryotic Cells
- Eukaryotic Cells
What are Prokaryotic Cells?
- Do not have a membrane-bound nucleus or organelles
- Surrounded by a capsule for protection
- All single-celled organisms
- Genetic material can be either DNA or RNA
- Reproduce by binary fission (asexual reproduction)
What are Eukaryotic Cells?
- Have a true membrane-bound nucleus and cell organelles
- Contain mitochondria
- Cell wall is the outermost layer
- Genetic material is DNA
- Cells divide via Mitosis (sexual reproduction)
What are the 5 roles of the Plasma Membrane (surround every cell)?
- Partially permeable, controlling the transport of molecules in and out
- Separates the contents of the cell from the outside
- Allows cells to signal each other
- A site for Biochemical reactions
- Allow cells to change shape
What do scientists refer to the Plasma Membrane as?
The Fluid Mosaic Model
Why is the Plasma Membrane also known as The Fluid Mosaic Model?
Fluid - individual phospholipid molecules can move relative to each other providing a flexible structure
Mosaic - Proteins and other components embedded within the bilayer vary in shape, size and pattern
What is the function of Phospholipids?
Allow lipid-soluble substances to enter/exit the cell, prevent water-soluble substances entering/exiting the cell and provide flexibility
What is the structure of Phospholipids?
- A bilayer (two layers of phospholipids facing opposite ways)
Hydrophilic head which is attracted to water (interact with water within the cytoplasm of the cell and external to the cell)
Hydrophobic tails which repel water (point into the centre - contain fatty acids)
What proteins are in the Plasma Membrane?
- The proteins are arranged more randomly
- They are embedded in the phospholipid bilayer in two main ways;
1. Extrinsic/Peripheral Proteins
2. Intrinsic/Integral Proteins
What are Extrinsic/Peripheral Proteins?
Free proteins on cell membrane surface or bound to an integral protein. Act as receptors, enzymes and facilitate movement.
What are intrinsic/Integral Proteins?
Act as carriers and channels of molecules that cannot diffuse through the membrane e.g. amino acids, sugars and ions
What are Glycoproteins?
Comprise of protein and carbohydrate chains. Play a role within cell recognition and help the cell attach to other cells
What are Glycolipids?
Lipids with a Carbohydrate attached. Provide energy and help to maintain stability of the membrane.
What is Cholesterol?
Controls membrane fluidity and keeps cells stable at body temperature (prevents bursting). More cholesterol = less fluidity.
What is the Concentration Gradient?
A difference between concentrations, usually the difference inside and outside the cell
What is Adenosine Tri Phosphate (ATP)?
Energy source produced by the mitochondria - catalyst of most reactions in cells
What are the 2 different methods of Cell Transport?
- Active Transport
- Passive Transport
What is Active Transport?
- Uses energy in the form of ATP.
- Endocytosis and Pinocytosis
What is Passive Transport?
- Does not use energy
- Osmosis and Diffusion
What is Simple Diffusion (Passive)?
Passive movement of substances from a higher concentration to a lower concentration.
Primarily used during gaseous exchange e.g. Oxygen
What is Facilitated diffusion?
Involves molecules (membrane proteins) to move molecules in or out of a cell. Channel proteins open and close to allow substances through.
Carrier proteins aid transport across the membrane by allowing molecules to bind to them
What is Osmosis?
The movement of water from a low solute concentration down the concentration gradient to a higher solute concentration
What is Isotonic Osmosis?
Movement of water in and out will occur at the same rate
What is Hypertonic Osmosis?
Cell will shrivel due to loss of water
What is Hypotonic Osmosis?
Cell will take up more water, become bloated and burst
Active Transport
Helps molecules that need to move against the concentration gradient (low to high - osmosis)
This requires ATP a by-product of cellular respiration
Describe the first step of a Sodium-Potassium Pump (AT)
The Sodium-potassium pump binds three sodium ions and a molecule of ATP
Describe the second step of a Sodium-Potassium pump (AT)
The splitting of ATP provides energy to change the shape of the channel. The sodium ions are driven through the channel.
What is the third step of a Sodium-Potassium Pump (AT)
The sodium ions are released to the outside of the membrane, and the new shape of the channel allows two potassium ions to bind
Describe the fourth step of a Sodium-Potassium Pump (AT)
Release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane
What is Endocytosis (Into the cell)?
- Large molecules are able to ENTER the cell; the membrane shape is changed due to ATP
- Two types of endocytosis:
1. Phagocytosis
2. Pinocytosis
What is Exocytosis (Out of the Cell)?
- Large molecules are able to EXIT the cell; the membrane shape is changed due to ATP
- Exocytosis allows waste materials and cellular products to be removed
What is Phagocytosis?
- The plasma membrane surrounds a molecule and engulfs it
- A vacuole is created where enzymes digest the molecule
What is Pinocytosis?
- The plasma membrane surrounds droplets of fluid and engulfs it
- The droplets of fluid are held in a vesicle that contains dissolved solutes that the cell needs
What are the two types of microscopes?
Light and Electron
What size can a light microscope go to?
400 nanometres
What size can an electron microscope go to?
10 million X bigger
What are the two types of electron microscopes
Transmission
Scanning
What do you use transmission microscopes for
Seeing through specimens, splitting them in half, allowing you to see the cellular structure
Understand how viruses invade cells
Arrangement of atoms
What do use scanning microscopes for
it scatters electrons across the surface so you have a more detailed image of the surface structure
What are the pros of light microscopes?
- illuminating source is light
- specimen preparation takes a few minutes
- live or dead specimens can be viewed
- image can be coloured
- no need for high voltage electricity
- no risk of radiation
- used f the study of detailed gross internal structure
What are the cons of light microscopes?
- Has a low resolving power
- Has a magnification of us to X1500
What are the pros of electron microscopes?
- Has a high resolving power
- Has a magnification of us to X300,000
- Used in the study pf external surface, ultra surfaces of cells and very small organisms
What are the cons of electron microscopes?
- Illuminating source is a beam of electrons
- Specimen preparation takes a few days
- Only dead specimens can be viewed
- Image is black and white
- High voltage electricity current required
- Risk of radiation
What is magnification?
the number of times greater the image is then the specimen
What is resolution?
the ability to distinguish between two points on an image
What is the magnification equation?
image size/actual size
e.g. 15/0.075 = 2,000X
Which two lenses does a light microscope use?
The eyepiece and Objective lens
What is Gram Staining use to distinguish between?
Differentiate two large groups of bacteria based on their different cell wall constituents
What is Gram positive?
Gram positive cells stain violet due to the presence of a thick layer of peptidoglycan in their cell walls, which retains the crystal violet the cells are stained with
What is Gram negative?
Gram negative cells stain red because of a thinner peptidoglycan wall, which does not retain the crystal violet during the decolouring process
What is the process of Gram staining?
- Staining with a water - soluble dye called crystal violet
- Decolourisation
- Counterstaining, usually with Serafin
