2.1.1 Cell Structure

Name the organelles involved in protein synthesis

Nucleus, ribosomes, RER, Golgi apparatus and cell surface membrane

Name the 4 different microscopes

Light microscope, transmission electron microscope (TEM), scanning electron microscope (SEM) and a laser scanning confocal microscope

What are the 2 general types of microscope?

Light microsope and electron microscope

What is magnification?

The degree to which the size of an image is larger than the viewed object itself, or, the increase in the size of an object to produce a magnified image

What is the formula for magnification?

M = I/A

What is resolution/the resolving power?

The degree to which it is possible to distinguish between two objects that are very close together

What does resolution depend on?

the wavelength of light that forms the image along with characteristics of the objectives

What happens if two objects are closer than half the wavelength of the radiation used in the microscope?

The objects cannot be resolved into two distinct points

Why do electron microscopes have higher resolving power than light microscopes?

They have a shorter wavelength of radiation (they use an electron beam)

How many mm in micrometers>

1mm = 1000um

How many mm in nanometers?

1mm = 1,000,000nm

How many micrometers in a nanometer

1um = 1000nm

How can you increase the resolution?

Use an objective lens with a short focal length, or place a medium with a high refractive index between the specimen and the objective lens (immersion oil)

How can you calibrate the microscope?

Measure the eyepiece graticule using the stage micrometer and then use this measurement as a calibration

What is the magnification of a light microscope vs an electron microscope?

Light microscope = x1500

TEM = x500,000 SEM = x100,000

What is the resolution of a light microscope vs an electron microscope?

Light microscope = 200nm

TEM = 0.2nm

SEM = 0.5

Describe the images produced with a light microscope

It is a 2D colour image that is virtual on the retina and can be viewed on a fluorescent screen using a projection light microscope

Describe the images produced with a TEM microscope

It is a 2D black and white image. Internal structures can be seen.

Describe the images produced with a SEM microscope

It is a 3D black and white image. Surface structures are seen, but you cannot obeserve the internal structures

Describe the images produced with a Laser Scanning microscope

It is a 3D black and white image. Multiple depths of the tissue are scanned to build up the image. External and internal 3D structures can be viewed at a very high resolution

Why do we use stains?

They improve definition and allow us to see organelles more clearly

What are coloured stains used for?

Coloured stains bind to specific chemicals on or in the specimen. Some stains bind to specific structures e.g methylene blue stains DNA. We need stains because most tissue is transparent and so lets light and electrons pass through.

What is differential staining?

It involves the use of more than one stain on the specimen. It contrasts different sub-cellular parts against each other.

Give 2 advantages and 2 disadvantages of light microscopy

The specimen can be viewed alive or dead and you can see natural colours. However it has a low magnification and resolution

Give examples of organelles you could see with a light microscope

Mitochondria and chloroplasts (not ribosomes!)

Give 2 advantages and 2 disadvantages of EM

Ultrastructure can be viewed with TEM and SEM gives depth of field. However the specimen has to be dead and dehydrated

Why does the specimen need to be dehydrated in EM?

EM uses a vacuum and water boils at room temp in a vacuum

Give examples of organelles you could see with a EM

Ribosomes, endoplasmic reticulum and lysosomes

What is the total magnification on each of the lenses on a light microscope?

x40, x 100, x400

What is the coarse focus wheel used for?

Used to focus the low and medium power lenses

What is the fine focus wheel for?

Used to focus the high power lens

Why might the size of cell structures be inconsistent?

Cell structures are 3D and may have been cut on different planes, resulting in inconsistencies

What are eukaryotic cells?

Cells with a true nucleus and other membrane bound organelles

What are prokaryotic cells?

Cells with no true nucleus. Nuclear material is not membrane bound and instead floats freely in the cytoplasm

What is the structure of the nucleus

The nucleus is the largest cell organelle in animal cells and is surrounded by a double membrane

What is the funtion of the nucleus?

It contains chromatin (DNA + protein) and controls the activities of the cell

What is the function of the nucleolus?

It manufactures ribosomes composed of ribosomal RNA and protein, using its own DNA

What is the structure of the nuclear envelope?

It is a double membrane with nuclear pores. The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum

What is the function of the nuclear envelope?

The nuclear pores allow the transportation of proteins into the nucleus and allows mRNa to leave during protein synthesis.

What is the structure of the RER?

It is an interconnected extensive system of membranous tubules called cisternae, which is continuous with the outer membrane of the nuclear envelope. It has ribosomes on its surface.

What is the function of the RER?

It folds and processes proteins made by the ribosoes, then transports them to the Golgi and thorughout the cell

What is the structure of the SER?

It is an interconnected system of membranous tubules called cisternae, however it often appears more tubular than the RER and has no ribosomes attached.

What is the function of the SER?

It is responsible for the synthesis of steroids and detoxification, so it is particularly numerous in the liver.

What is the structure of the Golgi apparatus?

It is a stack of flattened membraneous sacs (cisternae), along with vesicles continuously being formed from the ER at one end and budding off the Golgi at the other

What is the function of the Golgi apparatus?

It processes, packages, modifies and transports proteins made on ribosomes. It adds signals for the destination of protein packges in vesicles

What are vesicles?

Membrane bound sacs used to carry substances around cells

Describe the interrelationships between organelles involved in the production and secretion of proteins

The nucleolus manufactures a molecule of mRNa via transcription. The mRNA strand then leaves via a nuclear pore and attaches to a ribosome on the RER. The ribosome synthesises a protein through translation which then passes into the RER to be folded and processed. The processed proteins are then transported by vesicles to the Golgi apparatus and fuse, releasing the proteins. They are prepared for secretion and the modified proteins leave the Golgi and fuse with the cell surface membrane, releading the proteins

Where would you find lots of Golgi apparatus organelles

They are well developed in secretory cells e.g the intestine

What is the structure of ribosomes?

They are small organelles composed of two subunits that are often attached to the RER but can also be found free in the cytoplasm. They are not membrane bound

What is the function of ribosomes?

They are the site of protein synthesis. The subunits bind eith mRNA and start translation. Free ribosomes make proteins used in the cytoplasm.

What is the structure of the mitochondria?

Double membrane structure where the inner membrsne is foled into cristae. Inside the mitochondira is a matrix which provides a large surface area for the attachment of proteins and enzymes required for aerobic respiration. It contains its own circular DNA

What is the function of mitochondria?

They are the site of aerobic respiration. They produce ATP and synthesis lipids and phospholipids. They can divide by themselves to make more mitochondria in more active cells

Where would you find lots of mitochondria?

Cells with a high metabolic activity have many well developed mitochondria e.g heart muscle cell

What is the structure of chloroplasts?

They are large, double membrane bound organelles. Thylakoid membranes are aranged in the form of stacked grana joined by lamellae and surrounded by stroma. It contains its own circular DNA

What are grana?

Stacked flattened discs that make up the thylakoids

What are lamellae?

Connecting membranes

What is stroma?

A fluid containing enzymes for making organic compounds

What is the function of chloroplasts?

They are the site of photosynthesis

What is the structure of flagella?

Long cylindrical hair-like extensions that stick out from the surface of cells. They are made from protein microtubules in a 9+2 arrangement

What is the structure of cilia?

Short cylindrical hair-like extensions that stick out from the surface of cells. They are made from protein microtubules in a 9+2 arrangement

Do prokaryote flagella have the 9+2 arrangement?

No, only eukaryotes

What is the difference between cilia and flagella?

Cilia are shorter and more numerous, whereas flagella are longer and only have one or a few on cells

What is the function of flagella and cilia?

They move organisms through a liquid medium. Cilia also move fluid past a cell e.g in the trachea

What is the structure of centrioles?

2 hollow cylinders positioned at right angles to each other

What is the function of centrioles?

They are used to form sindle fibres in nuclear division

What is the structure of plant cell walls?

They are made of cross-linked chains of cellulose which form sieve-like networks of strands. It is found on the outside of the cell surface membrane of plant cells

What is the function of plant cell walls?

The sieve like strands give strength and shape, and the internal pressure gives turgidity which supports the plant and prevents it from bursting

What is the structure of the cytoskeleton?

Interconnected system of fibrous proteins in the cytoplasm - microtubules and microfilaments . It is found between organelles and can be assembled or dismantled in seconds. It constantly changes.

What is the function of the cytoskeleton?

Strength and support, movement of cellular structures and materials

How does the cytoskeleton provide strength and support?

It provides mechanical strength to cells and holds organelles in place. It acts like a scaffolding and maintains the shape of the cell.

How does the cytoskeleton enable cell mobility?

It aids transport within cells by providing tracks along which organelles can move e.g chloroplasts

What is the structure of lysosomes?

They are a special type of vesicle which contains hydrolytic enzymes.

What is the function of lysosomes?

They break down waste materials such as worn-out organelles

What is the structure of the plasma membrane?

It is a selectively permeable double layer of phosopholipids, glycolipids, cholsesterol and proteins

What is the function of the plasma (cell surface) membrane?

It controls the entry and exit of materials into and out of cells. It separates the internal aqueous environment of the cell from the aqueou external environment

List the similarities and differences between prokaryotic and eukaryotic cells

Prokaryotes are much smaller. Prokaryotes have circular DNA in the cytoplasm whereas eukaryotic DNA is associated with histones and and formed into chromosomes. Prokaryotes = 70S ribosomes Eukaryotes = 80S ribosomes. Prokaryotes have no membrane bound organelles wheres eukaryotes do. Prokaryotes have a peptidoglycan cell wall whereas plants have cell walls made of cellulose.