F211 Cell Structure Flashcards
Magnification
Formula
Magnification = Image Size / Actual Size
Magnification
Definition
Degree to which size of image is larger than the object itself
Resolution
Definition
Degree to which it’s possible to distinguish between two objects that are close together
Light Microscope
Magnification
1500x
Scanning Electron Microscope
Magnification
100 000x
Transmission Electron Microscope
Magnification
500 000x
Light Microscope
Advantages
Relatively cheap
Easy to use
Portable
Light Microscope
Disadvantages
Low resolution
Can’t give a detailed picture of internal cell structure
Light Microscope
Resolution
200nm
Light Microscope
Specimens
Wide range of organisms including:
Live organisms
Thin sections of larger plants and animals
Smear preparations of blood or cheek cells
Not for internal cell structure as the resolution isn’t high enough
Light Microscope
Specimen Preperation
- Staining - coloured stains allow the specimen to be seen easier e.g. acetic orcein stains DNA red, gentian violet stains bacterial cell walls
- Sectioning - specimens are embedded in wax allowing thin sections to be cut without distorting the structure, useful for soft tissue e.g. brain
Light Microscope
Function
- Light passes from a bulb under the stage, through a condenser lens, then through the specimen
- The beam of light is focused through the objective lens, then through the eye piece lens
- Different objective lenses can be rotated into position to change the magnification
Scanning Electron Microscope
Function
- The electron beam is directed at the sample
- Electrons aren’t absorbed, they are bounced off the sample
- The final image is produces a 3D. IWW of the surface of the sample
Electron Microscopes
Advantages
Resolution is 0.2nm
Can be used to produce detailed images of the structures (organelles) inside the cell
The SEM produces 3D images
Electron Microscope
Limitations
Samples have to be placed in a vacuum or electron beams are deflected by molecules in the air
Extremely expensive
Preparation of samples and microscope operation requires a high degree of skill and training
Vesicles
Definition
Membrane bound sacs found in cells
Used to carry various substances around cells
Nucleus
Structure
Surrounded by a nuclear envelope
The nuclear envelope is a structure made of two membranes separated by fluid
Holes called nuclear pores go right through the envelope and allow relatively large molecules to pass through
The nucleolus is a dense spherical structure inside the nucleus
When stained the nucleus shows darker patches known as chromatin
Nucleus
Function
Contains nearly all the cells genetic material
The chromatin consists of DNA and proteins, it has the instructions for protein synthesis
Some of these proteins regulate the cells activity
When cells divide chromatin divides in to two visible chromosomes
The nucleolus makes RNA and ribosomes which pass out into the cytoplasm
Transmission Electron Microscope
Function
- The electron beam passes through a very thin prepared sample
- Electrons pass through denser parts of the sample less easily giving some contrast
- Produces a final 2D image
Rough Endoplasmic Reticulum
Structure
Series of flattened membrane bound sacs
Studded with ribosomes
Rough Endoplasmic Reticulum
Function
Transports proteins that were made on the attached ribosomes
Some proteins may be secreted from the cell
Some proteins will be placed on the cell surface membrane
Smooth Endoplasmic Reticulum
Structure
Series of flattened membrane bound sacs called cisternae
No ribosomes
Fairly evenly distributed throughout the cell
Smooth Endoplasmic Reticulum
Function
Involved in making the lipids that a cell needs
Mitochondria
Structure
Two membranes separated by a liquid filled space
The inner membrane is folded to form cristae
The central part of the mitochondrion is called the matrix
Golgi Body
Structure
A stack of membrane bound flattened sacs
Ribosomes
Structure
Tiny organelles
Some are free in the cytoplasm
Some are bound to endoplasmic reticulum
Each is made up of two subunits
Ribosomes
Function
Site of protein synthesis in the cell
Golgi Body
Function
Receives and modifies proteins from the ER
May add sugar molecules to them
Packages the modified proteins into vesicles that can be transported
Some modified proteins may go to the surface of the cell to be secreted
Mitochondria
Function
Produce most of the adenosine triphosphate (ATP) during respiration
Almost all activities that take place in the cell are driven by energy released from ATP
Contain their own mitochondrial DNA, genes which are essential for respiration
Plasma Membrane
Structure
Phospholipid bilayer
Channel and carrier proteins
Glycoproteins and glycolipids
Cholesterol between phospholipids
Plasma Membrane
Function
Protects the cell from its surroundings
Selectively permeable
Controls the movement of substances in and out of the cell
Cellulose Cell Wall
Structure
Primary cell wall made up of cellulose microfibrils, pectin and soluble proteins
Primary cell wall in between plasma membrane and middle lamella
Cellulose Cell Wall
Function
For support and structure
Protection against mechanical strength and infection
Enables the transport of substances in and out of the cell
Vacuole
Structure
Membrane bound mass of fluid containing nutrients and waste products
Surrounded by tonoplast membrane
Vacuole
Function
Isolates and stores materials within a cell
Lysosomes
Structure
Spherical sacs surrounded by a single membrane
Lysosomes
Function
Contain powerful digestive enzymes to break down materials in the cell
Chloroplasts
Structure
Two membranes separated by a fluid filled space
Inner membrane is continuous
Inside the membranes is an elaborate network of flattened membrane sacs called thylakoids
Stacks of thylakoids are called grana (granum singular)
Chlorophyll molecules are present on the thylakoid membranes and the inter granal membranes
Flagella
Function
Propels a cell
Used for movement
Allows a cell to move
Cilia
Structure
Short extensions if eukaryotic cells
Hair like appearance
Cilia
Function
May be used for locomotion
Used to move fluids or mucus over a surface
Chloroplasts
Function
Site of photosynthesis in plant cells
Flagella
Structure
Whip like structure
Centrioles
Structure
Small tubes of protein fibres
There is a pair of the next to the nucleus in animal cells and in the cells of some protoctists
Centrioles
Function
Take part in cell division
Form fibres known as the spindle which move chromosomes during nuclear division
Micro Filament
Size
7nm
Protein Synthesis
Transcription
The base sequence of the DNA is copied on to the mRNA
Protein Synthesis
mRNA travels to ribosome
Single stranded mRNA leaves the nucleus through a nuclear pore
Enters the cytoplasm to find a ribosome either attached to the rough Endoplasmic reticulum or free in the cytoplasm
Protein Synthesis
Stages
Transcription mRNA travels to ribosome Translation Primary structure of polypeptide enters RER where it assumes secondary and tertiary structures Modified and packaged in the Golgi body Exocytosis
Cytoskeleton
A network of fine filaments or fibres that run through the cytoplasm of a cell There are three types of filament 1. Micro filaments 2. Intermediate Filaments 3. Microtubles
Micro Filament
Composition
Long thin stringy proteins
Mostly actin
Protein Synthesis
Translation
Occurs at the ribosome
The base sequence on the mRNA is ‘read’ and used to join the correct amino acids together in the correct sequence to form the primary structure of a polypeptide
Protein Synthesis
Rough Endoplasmic Reticulum
Primary structure if the polypeptide enters the rough Endoplasmic reticulum
As it moves through the RER it assumes its secondary and tertiary (3D) structure
The polypeptide is packaged into a vesicle and pinched off of the RER
The cytoskeleton is involved in transporting the vesicle to the Golgi body
Micro Filament
Function
Help cells move
Protein Synthesis
Golgi Body
The vesicle fuses to become one of the flattened sacs of the Golgi body
The Golgi body modifies the protein and packages it into a vesicle
The vesicle is pinched off the Golgi body and carried by the cytoplasm to the cell membrane
Protein Synthesis
Exocytosis
The vesicle fuses to the cell surface membrane and ten protein is released out of the cell
Intermediate Filament
Size
8-10nm
Function of the Cytoskeleton
Moving organelles around the cell
Supports the structure of the cell
Hold organelles in place inside the cell
Transports vesicles around the cell
Intermediate Filament
Composition
Rope like and fibrous
Variety of proteins
Intermediate Filament
Function
Increase cellular stability
Provide mechanical strength to cells and tissues
Resist stress
Microtubles
Size
25nm
Microtuble
Composition
Thick strong spirals of thousands of subunits made of protein - tubulin
Microtuble
Function
Helps with various transport functions
Can move a microorganism through a liquid
Used to waft liquid past a cell
