Cells

Magnification

Magnification

How much larger the image size is compared to the actual object

Resolution

The ability to distinguish between 2 separate points.

What is the max magnification and resolution of a light microscope

Mag- x1500

Res- 0.2 micrometre

Whats a light microscope

Shines a beam of light through specimen. It has a long wavelength so lower resolution because if object is smaller than 0.2 micrometer it will appear as one object.

Whats an electron microscope

Uses a beam of electron in a vacuum at a dead specimen. It has a short wavelength so higher resolution because it can pass through every part of the specimen so will appear clearer.

Whats the max magnification and resolution of an electron microscope.

Max resolution- 0.2nm

Max mag - x1,500,000

Transmission Electron Microscope (TEM)

A beam of electrons that pass through specimen. Denser areas absorb more electrons so appear darker on image.

What are the advantages of TEM?

Higher resolution - 0.1nm

High magnification - x500,000

Why must the electron microscope be used ina vacuum?

The electrons may be absorbed by the air, so not enough electrons would be absorbed by the specimen creating an unclear image. The electrons would be scattered.

What is a Scanning Electron Microscope (SEM)

Beams of electron scattered, bouncing off of specimen to form 3D images

Hat are the advantages of SEM

Thick specimen

Forms 3D iage

Max mag- x250,000

Max resolution - 20nm

Limitations of SEM

Lower resolution

Dead specimens

Black and white image

Lower resolution

What is cell fractionation?

Breaking up whole cells to release all of the organelles inside to study their functions

Before cell fractionation can start, the tissue is placed in a cold, buffered solution with the same water potential as the tissue. Why cold?

To reduce enzyme activity, that might break down organelles.

Before cell fractionation can start, the tissue is placed in a cold, buffered solution with the same water potential as the tissue. Why buffered?

So the pH doesnt fluctuate, changes in pH can change structure of organelles or affect the functioning of enzymes.

Before cell fractionation can start, the tissue is placed in a cold, buffered solution with the same water potential as the tissue. Why with the same water potential?

To prevent osmosis so the organelles to shrink or burst

What is homogenation?

Cells are broken up by a homogeniser to release organelles. The resultant fluid is known as the homogenate. Its filtered to remove any whole cells or large debris

What is ultracentrigugation?

Fragments in the filtered homogenate are separated in a centrifuge. This spins the tube at high speeds to produce a centrifugal force.

Describe the process of ultracentrifugation

The tube is spun at a low speed in the centrifuge

The heaviest organelle - nucleus collects at the bottom and the lightest fluid collects at the top

The supernatant is removed and placed into another test tube

The centrifuge is spun at a higher speed.

What are the ultra structures of chloroplasts

What are the ultrastructures of mitochondria?

Double membrane- controls what leaves and enters

Cristae- inner membrane folded over to give large surface area for attachment of enzymes and proteins for respiration

Matrix- makes up the rest of the mitochondria- proteins found here to help production of their own proteins. Many enzymes involved in respiration are found here.

What are the ultrastructures of Golgi apparatus?

Folded flatten sacs surrounded by vesicles

Processes, packages and labels lipids and proteins to be sent to correct destination.

Add carbohydrates to proteins and lipids

Modified proteins are sent to vesicles where it merges with cell membrane and released out.

Forms lysosomes

What are the ultrastructures of lysosomes

Vesicles containing digestive enzymes such as lysozymes that break down cell walls of bacteria.

Digests worn out cells

Breaks down cells after they have died

What are the ultrastructures of ribosomes

2 sub units and site of protein synthesis

Each sub uniit has ribosomal RNA and protein.

Eukaryotic cells are 80S

Prokaryotic cells are 70S

What are the ultrastructures of cell walls

Consists of microfibrils of cellulose embedded in matrix

Cellulose contributes to cells strength

Middle lamella -boundary between adjacent walls and cements them together

Prevents bursting, allows water in, provides strength

What are the ultrastructures of a vacuole

Fluid filled sac bound by single membrane - tonoplast

Contains solution of amino acids, salts,sugars,wastes and some pigments

Makes cells turgid

Sugars and amino acids are food storage

Pigment colour petals to attract pollen insecte

Ultrastructures of nucleus

Nuclear envelope- double membrane, outermemebrane is continuous with ER of cells

Nuclear pores- 3000 pores for large molecules like mRNA

Nucleoplasm- granular, jelly like substance that takes up rest of the space.

Chromosomes- chromatin- protein and DNA that control cell activity

Nucleolus- site of ribosome production

Ultrastructures of chloroplasts

Chloroplasts envelope- double membrane

The grana - stack of 100 thylakoids for first stage of photosynthesis

Thylakoids- holds chlorophyll extension to connect to other grana

Stroma- fluid filled matrix- second stage of photosynthesis

Ultrastructures of endoplasmic reticulum

Rough ER - flattened sacs enveloped by membrane with ribosomes on surface. Synthesises and transports rproteins made at ribosomes

Smooth- more tubular shaped, lacks ribosomes. Synthesises, stores and transports carbohydrates and lipids

If all cells contain the same genes, how are cells specialised?

Genes are switched on or off

Epithelial cells

Sheets of cells where the body meets the outside world

Squamous epthelial

Thin single layer of cells , closely packed together , each attached to basement membrane

Cells are thin so nucleus creates a bump and provides a short diffusion distance

Found in alveoli of lungs, walls of blood capillaries, in renal capsule of kidneys, lining of ducts, arteries and veins

Ciliated epithelial

Single layer , cube shaped or column cells attached to basement membrane

Cilia is present opposite basement membranes, moves mucus and other materials

Found in trachea, bronchi, oviduct

Why are arteries and veins organs but capillaries aren’t?

Arteries and capillaries are organs because they are made of different tissues that performs one function. They contain squamous, muscle and connective tissue.

But capillaries are only made up of one type of tissue.

Why is the stomach an organ?

Muscle tissues to churn up food

Epithelial cells to protect the stomach wall and produce secretions

Connective tissues to connect other tissues together

Why is a leaf an organ

Palisade mesophyll tissue to carry out photosynthesis

Spongy mesophyll for gas diffusion

Epidermis to protect the leaf and for gas diffusion

Phloem to transport organic material away from the leaf

Xylem transport water and minerals into leafs

Prokaryote

A single celled organism that contains no nucleus and membrane bound organelles

Differences of nucleas in eukaryotes and prokaryotes

Prokaryotes - no nucleus or membrane bound organelles

Eukaryotes- have a nucleus and membrane bound organelles

Difference in size between prokaryotes and eukaryotes

Prokaryotes are smaller than eukaryotes

Difference in DNA in prokaryotes and eukaryotes

Prokaryotes- circular DNA, floats free in cytoplasm, no protein coat

Eukaryotes - linear DNA , wrapped around by proteins(histones), contained in a nucleus

Structures in prokaryotes not found in eukaryotes

Plasmids sometimes containing antibiotic resistance genes

Pilli attach to other bacterial cells, DNA is stolen and forms new plasmid in donor

Thick protective slimy capsule to retain moisture and protect itself from hosts immune system

Some have flagellum that creates locomotion

Mesosmes- inner foldings of the inner membrane which contain enzymes required for respiration. Increases SA of cell.

Difference in ribosomes between prokaryotes and eukaryotes

Prokaryotes have 70S and eukaryotes have 80S

Difference in cell walls in prokaryotes and eukaryotes

Prokaryotes- cells walls made up of glycoproteins called peptidoglycan (Murein)

Eukaryotes- plants have cellulose in cells walls and fungi have chitin in cell walls

Describe the structure of viruses

Acellular, non living structures, consisting of nucleic acids either DNA OR RNA enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope

They also have attachment proteins that bind to proteins that bind to receptors on host cells

What are the 5 stages of binary fission

1. Circular DNA, plasmids replicated

2. Cell get bigger and DNA moves at bigger ends of cell

3. Cytoplasm divides and new cell wall forms

4. Cell wall completely forms creating 2 daughter cells

5. Each daughter cell contain one copy of circular DNA but can variable amounts of plasmids.

What is the Endosymbiosis theoryhough that eukaryotic cells

It is thought that eukaryotic cell organelles like nuclei, mitochondria, chloroplast are derived from prokaryotic cells that became incorporated inside larger prokaryotic cells

What observation supports endosymbiosis

• Organelles contain circular DNA, like bacterial cells

• Contains 70S ribosomes

• Organelles have double membranes, as tough a single membrane cell had been engulfed and surrounded by a larger cell

• Organelles reproduce by binary fission like bacteria

• Orgenelles are very alike to some bacteria that are still alive today

What is mitosis

Cell division that results in each of the daughter cells having an exact copy of the DNA of the parent cell.

Occurs in eukaryotic cells

What occurs during Interphase of mitosis

Chromosomes aren’t visible yet.

DNA is replicated and joined at the centromere

What occurs at the prophase stage of mitosis

Chromosomes become visible by condensing . Animal cells have centrioles that move to opposite ends of the cell. The nuclear envelope breaks down and nucleolus disappears. Chromosomes are free in the cytoplasm, and drawn to equator of the cell by spindle fibres attached to centromere.

What do plant cells have instead of spindle fibres

Spindle apparatus but don’t need centrioles.

What occurs in the metaphase stage in mitosis

Double chromatids formed. spindle fibres begin to attach to centromere on each sister chromatid

Chromosomes line up on equator of cell

What occurs in the anaphase stage of mitosis

Centromere divide into 2 and spindle fibres pull the individual chromatids apart, moving to opposite ends of the cell

WHat occurs at the telophase stage of Mitosis

Chromosomes reach opposite ends of poles, becoming longer and thinner therefore disappearing. It leaves behind spread out chromatin

Nuclear envelope and nucleolus re form.

What occurs at the cytokinesis stage of mitosis

The cytoplasm divides and 2 daughter cells form containing genetically identical information.

Each daughter cell starts the interphase part of the cell cycle

What are plasma membranes

Membranes surrounding cells and cell organelles

What are cell surface membrane

The membrane surrounding the cell

Where are phospholipid bilayer found

Cell surface membrane

Structure of phospholipid membrane

Hydrophillic polar, phosphate group head that attracts water so face outwards

Hydrophobic tail made of fatty acids (non polar) that repels water so faces inwards

Functions of phospholipids in membrane

Allow lipid soluble substances to enter and leave the cell

Prevent water soluble substances entering and leaving the cell

Make the membrane flexible and self sealing

What are the function of proteins that are only on the inner or outer surface (peripheral)of phospholipid bilayer?

For mechanical strength

Connects glycoproteins that acts as receptors together with glycolipids

What are the function of integral proteins( spans the phospholipid bilayer from one side to the other)

Protein channels - facilitates diffusion of water of water soluble ions across the membrane

Carrier proteins - bind to large molecules and then change shape in order to move these molecules across the membrane

What is the function of cholesterol within the phospholipid bilayer?

Add strength to cell surface membrane

Hydrophobic so prevent water loss and dissolved ions from cell

Reduce lateral(side to side)movement of fatty acids of phospholipids, without not making the cell too rigid.

Makes membrane less fluid at high temperatures

Functions of glycolipids in the phospholipid bilayer

Acts as recognition sites

Helps maintain stability of the membrane

Helps cells to attach to one and other so form tissues

What are glycolipids and their functions

Carbohydrate chains attached to extrinsic proteins

Acts as recognition sites

Helps cells recognise each other to form tissues

Help lymphocytes recognise their own cells

What properties would prevent substances to pass through cell surface membrane?

Non lipid soluble substances(non polar)

Water soluble(polar molecules)

Electrically charged molecules.

Large molecules

Why is it called the fluid mosaic model?

Fluid- phospholipid molecules move relative to one another so constantly changing in shape

Mosaic- proteins embedded in the phospholipid bilayer vary in shape size and pattern

What affects the phospholipid bilayer to be more fluid

Higher temperature

More fatty acids

Shorter tails

What affects the phospholipid bilayer to be less fluid

More cholesterol

What does passive mean

Processes rely on inbuilt kinetic energy of the molecules not ATP released from respiration.

Do particles stop moving when they reach equilibrium

All particles are constantly in random motion due to the kinetic energy they possess

What is diffusion

Net movement of molecules or ions from a area of high concentration to an area of low concentration until evenly distributed

What type of molecules can pass through cell surface membrane?

Small, non polar molecules such as oxygen and carbon dioxide.

Facilitated diffusion

Charged ions ands polar molecules can’t diffuse easily because of the hydrophobic nature of the tails, so they need protein channels and carrier proteins to get across the membrane.

Protein channels

Transports specific water soluble ions, through water filled hydrophillic channels.

Selective as it only opens in the prescience of a specific ions

Ion binds to protein, changing shape so it closes on one side of the membrane and opens it on the other side

Carrier proteins

Transports specific molecules e.g. glucose.

Specific molecules bind to proteins causing a change in shape. This causes particles to be released on the other side of the membrane

Osmosis

Net movement of water molecules or ions from an area of high water potential to an area of low after potential through a partially permeable membrane.

Why is there sometimes osmosis in the phospholipid bilayer

Water ions are weakly charged and is a small molecule

What is a solute

The substance that is being dissolved

What is the solvent

The substance the solute is being dissolved in

Solution

The solute dissolved in solvent

Aquaporins

Water selective Protein channels that facilitate diffusion of water

Water potential

Measure of pressure created by water molecules, units are kiloPascals.(kPa)

What happens to the water potential when a solute is added to pure water

It lowers and has a negative water potential because pure water has 0kPa.

What happens when more solute is added to pure water

The water potential lowers more because solution is more concentrated

Ie the more concentrated a solute the lower the water potential.

What prevents animal cells from bursting by osmsis?

Don’t have cell wall

Animals cells live in blood plasma which has the same water potential as the water potential inside red blood cell.