Cell Structure

Resolution

-min distance between two objects in which they can still be viewed as separate objects

-determined by the wavelength of light in a light microscope & by the wavelength of the electron beam in an electron microscope

Magnification

-How many times larger the image is compared to the object

-magnification= image size/actual size

Types of microscope

-light optical microscope

-transmission electron microscope

-scanning electron microscope

Eyepiece graticule

-small piece of glass with measurement scale etched on its surface that fits inside a microscope eyepiece

Calibrating the eyepiece graticule

-Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece

-Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale

-Each division on the micrometer is 10μm, so this can be used to calculate what one division on the eyepiece graticule is at the current magnification

differential staining

-technique involving many different chemical stains being used to stain different parts of a cell in different colours

E.g. crystal violet and acetic orcein

Stage micrometer

-A microscope slide that has a ruler/scaled bar etched into it.

-The scale is usually 1mm long and has 100 divisions so each division is 10μm.

-It is used to calibrate the eyepiece graticule.

How does TEM work

-sample must thin and stained

-beam of electrons passes through the sample used to create an image

-focused using electromagnets in a vacuum

TEM evaluations

-Highest revolving power

-High magnification

-Extremely thin specimens required

-Complex staining method

-Specimen must be dead

-Vacuum required

How does SEM work

-Beam of electrons pass across the sample used to create an image of the surface of the sample

-Focussed using electromagnets

SEM evaluation

-High resolving power

-High magnification

-Thick specimens unusable

-Complex staining method

-Specimen must be dead

-Vacuum required

what can you see with TEM

2D image of details within organelles

what can you see with SEM

3D image of the surface of cells and organelles

plasma membrane structure

Phospholipid bilayer with embedded intrinsic and extrinsic proteins

plasma membrane structure diagram

plasma membrane function

-Maintain structural integrity

-act as a barrier

-control passage of substances in and out of the cell

Nucleus structure

-Surrounded by a double membrane nuclear envelope with nuclear pores

-contains chromosomes with proteins bound, linear DNA

-Contains nucleolus to synthesise ribosomes

Nucleus function

contains DNA

site of transcription and primary mRNA splicing

mRNA splicing

Site of DNA replication

Nucleolus makes ribosomes

Nuclear pore allows movement of substances to/from cytoplasm

cilia structure

hair like projections out of cell

cilia function

-Can be mobile or stationary

-Mobile cilia help move substances in a sweeping motion

-Stationary cilia are important in sensory organs, such as the nose

flagella structure

whip like structure

mito structure

-dbl membrane with inner membrane folded into cristae

-Fluid-filled centre called matrix

-70S ribosomes in matrix

-Small, circular DNA

-Enzymes in matrix

mito function

site of aerobic respiration

atp production

centriole structure

-made of microtubules

-occur in pairs to form a centrosome

centriole function

-involved in production of spindle fibre

-organisation of chromosomes in cell division

lysosome structure

Vesicles formed from the golgi apparatus and which contain hydrolytic enzymes

lysosome function

-type of golgi vesicle that releases lysozymes to hydrolyse pathogens/cell waste products

cytoskeleton structure

-network of fibres found within the cytoplasm all over a cell

-Consists of microfilaments, microtubules and intermediate fibres

-Microfilaments are responsible for cell movement

-Microtubules are responsible for creating a scaffold-like structure

cytoskeleton function

-mechanical strength to cells

-maintain the shape and stability of a cell

-forms a network for organelles to move around the cell on

ribosome structure

Small organelles in cells made up of protein and rRNA

Ribosomes are made up of a small and large subunit (80S size in eukaryotes)

ribosome function

Site of protein synthesis

Site of translation in protein synthesis

RER structure

-RER = rough endoplasmic reticulum

-System of membranes with bound ribosomes that is often continuous with the nucleus

RER function

The site of protein synthesis (translation)

SER structure

SER = smooth endoplasmic reticulum

System of membranes with no bound ribosomes

SER function

Create, store and transport lipids chand carbohydrates

chloroplast structure

-double membrane bound organelle

cell wall structure

-found in plants, algae and fungi

-plants: made of polysaccharide cellulose

-fungi: made of chitin

-bacteria: peptidoglycan

cell wall function

-provides structural strength to cells

-prevents cells from bursting from osmotic pressures

-provides shape, support and structure

organelles involved in secretion of protein

-Polypeptide chains synthesised in the RER

-chains are packaged into vesicles to be sent to the golgi apparatus via the cytoskeleton

-they are to be modified

-from the golgi they are package into secretory vesicles carry the protein to the cell membrane

-to be released via exocytosis

contrast prokaryotic & eukaryotic cells

Prokaryotic cells are smaller

Prokaryotes have no membrane-bound organelles

Prokaryotes have smaller 70S ribosomes

Prokaryotes have no nucleus-circular

DNA is not associated with histones

Prokaryotic cell wall made of peptidoglycan instead of cellulose/chitin

Possible extra organelles of prokaryotes

Plasmids: loops of DNA

Capsule surrounding the cell wall: gives protection from the immune system

Flagella: locomotion

lysosome structure diagram