2.1 Cell Structure Flashcards
Magnification
How many times bigger the image produced is than the real life object
Resolution
Ability to distinguish between objects that are close together
Limits of Light microscopes
Impossible to distinguish between 2 objects that are closer than half the wavelength of light
Cannot be used to oversee smaller organelles such as ribosomes, endoplasmic reticulum or lysosomes
Electron microscopes
Can be used to observe ribosomes, endoplasmic reticulum or lysosomes
How do transmission electron microscopes work
Focus a beam of electrons which is transmitted through the specimen, denser parts appear darker which produces contrast between different parts of the object being observed
Advantages of transmission electron microscopes
They give high resolution images, this allows internal structures within cells to be seen
Disadvantages of transmission electron microscopes
Can only be used with very thin specimens
Cannot be used to observe live specimens
Lengthy treatment required to prepare specimens means that artefacts can be introduced
Don not produce colour image
How do Scanning electron microscopes work
Scans beam of electrons across the specimen, bounces off the surface of the specimen and the electrons are detected forming an image, producing three-dimensional images that show the surface of specimens
Advantages of scanning electron microscopes
Can be used on thick specimens
Allow the external,3-d structure to be observed
Disadvantages of scanning electron microscopes
Give lower resolution than transmission electron microscopes
Cannot be used to observe live specimens
Do not produce a colour image
How do Laser scanning confocal microscopes work
Cells must be stained with fluorescent dyes, a thick section of tissue are scanned with a laser beam which is reflected by fluorescent dyes, multiple depths of the tissue are scanned to produce an image
Advantages of laser scanning confocal microscopes
Can be used on thick, 3d specimens
Allow the sterna’s, 3d structure to be observed
Very clear images are produced
Disadvantages of laser scanning confocal microscopes
It is a slow process and takes a long time to obtain an image
Laser has potential to cause photo damage to the cells
IAM TRIANGLE
Image size= actual size/magnification
Order of units of measurement
1000 nanometer= a micrometer
1000 micrometer- millimetre
1000 millimetres= metre
Total magnification
Eyepiece lens magnification x objective lens magnification
Comparison between electron and light microscope
E- large and installation means can’t be moved, L- small and easy to carry
E- vacuum needed, L- no vacuum needed
E- complicated sample prep, L- easy sample prep
E- over x500,000 magnification, L- up to x2000 magnification
E- resolution 0.5nm, L- resolution 200nm
E- specimens are dead, L- specimens can be living or dead
What is Cell surface membrane
Formed from a phospholipid bilayer, partially permeable
Cell wall
Freely permeable to most substances
Found in plant cells not animal
Outside cell membrane and offer structural support to cell
Structural support provided by polysaccharide cellulose in plants
Nucleus
Present in all eukaryotic cells (except rbc)
Relatively large and separated by cytoplasm by the nuclear envelope which has many pores
Contains chromatins which is from which chromosomes are made
Nuclear pores
Allows mRNA and ribosomes to travel out of the nucleus as well as allowing enzymes and signalling molecules to travel in
Mitochondria
Site of aerobic respiration
Surrounded by double-membrane with the inner membrane folded to form Cristal
Cristal
Matrix formed by Cristae in mitochondria contains enzymes needed for aerobic respiration, producing atp
Chloroplasts
Found in plant cells
Site of photosynthesis
Contain chlorophyll
Ribosomes
Found in all cells
Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
Site of protein synthesis
80s ribosomes
Found in eukaryotic cells
70s ribosomes
In prokaryotes, mitochondria and chloroplasts
Rough endoplasmic reticulum
Found in plants and animal cells
Surface covered in ribosomes
Formed from continuous folds of membrane continuous with the nuclear envelope
Processes proteins made by the ribosomes
Smooth endoplasmic reticulum
Found in plant and animal cells
Does not have ribosomes on the surface
Involved in the production, processing and storage of lipids, carbohydrates and steroids
Golgi apparatus structure
Found in plant and animal cells
Flattened sacs of membrane similar to the smooth endoplasmic reticulum
Golgi apparatus function
Modifies proteins and lipids before packaging them into Golgi vesicles
Vesicles then transport the proteins and lipids to their required destination
Large permanent vacuoles
A sac in plant cells surrounded by the tonoplast, selectively permeable membranes
Vacuoles in animal cells are not permanent and small
Vesicles
Found in plant and animals cells
A membrane-bound sac for transport and storage
Lysosomes
Specialist forms of vesicles which contain hydrologic enzymes (enzymes that break down biological molecules)
Break down waste materials such as worn-out organelles
Used extensively by cells of the immune system
Centrioles
Hollow fibres made of microtubules
Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
Microtubules
Found in eukaryotic cells
Makes up cytoskeleton of the cell
Cytoskeleton
Used to provide support and movement of the cell
Microvilli
Found in specialised animal cells
Cell membrane projections
Used to increase the surface area of the cell surface membrane in order to increase the rate of exchange of substances
Cilia
Hair-like projections made from microtubules
Allows the movement of substances over the cell surface
Flagella
Found in specialised cells
Similar in structure to cilia, made of longer microtubules
Contract to provide cell movement for example in sperm cells
Structure found in only animal cells
Centrioles and microvilli
Structures found in only plant cells
The cellulose cell wall, large permanent vacuoles and chloroplasts
Organelles involved in protein synthesis
Nucleus, ribosomes, rough endoplasmic reticulum, Golgi apparatus, cell surface membrane
Nucleus in production of proteins
Stores the DNA (that codes for the production of proteins) and also contains the nucleolus, which manufactures ribosomes (required for protein synthesis)
Production of proteins 1
The DNA from the nucleus is copied into a molecule of mRNA via a process known as transcription
Production of proteins 2
The mRNA strand leaves the nucleus through a nuclear pore and attaches to a ribosome on the rough endoplasmic reticulum
Production of proteins 3
The ribosome reads the genetic instructions contained within the mRNA and uses this code to synthesise a protein via a process known as translation
Production of proteins 4
This protein passes into the lumen of the rough endoplasmic reticulum to be folded and processed, cells that produce a large number of proteins eg enzyme or hormone producing cells have a extensive rough endoplasmic reticulum
Production of proteins 5
The processed proteins are then transported into the Golgi apparatus in vesicles which fuses with the Golgi apparatus, releasing the proteins
Production of proteins 6
The Golgi apparatus modifies the proteins, preparing them for secretion proteins that go through the Golgi apparatus are usually exported, put in lysosomes or delivered to organelles
Production of proteins 7
The modified proteins then leave the Golgi apparatus in vesicles which fuse with the cell surface membrane releasing the proteins by the process of exocytosis
Cytoskeleton structure
Within the cytoplasm of cells, there is an extensive network of protein fibres
What is cytoskeleton made up of
Microfilaments and microtubules
Microfilaments
Solids strands that are mostly made up of protein-actin. These fibres can cause some cell movement and movement of some organelles within the cells by moving against each other
Microtubules
Tubular (hollow) strands that are mostly made up of the protein tubular> organelles and other cell contents are moved along these fibres using ATP to drive this movement
Functions of cytoskeleton
Strengthening and support, intracellular movement, cellular movement
Cytoskeleton- strengthening and support
Provides cell with mechanical strength, forming a kind of scaffolding that helps maintain the shape of the cell, supports the organelles keeping them in position
Cytoskeleton- intracellular movement
Aids transport within cells by forming tracks along which organelles can move eg. Movement of vesicles
Cytoskeleton- cellular movement
Enables cell movement eg, cilia and flagella, these structures are both hair-like extensions that protrude from the cell surface and contain microtubules that are responsible for moving them
What type of cells are animal and plant
Eukaryotic
What type of cells are bacteria
Prokaryotic
How are prokaryotic cells different to eukaryotic cells
Cytoplasm lacks membrane bound organelles
Ribosomes are structurally smaller (70s) (eukaryotic(80s))
No nucleus, instead single circular DNA molecule that is free in the cytoplasm and is nt associated with proteins
A cell wall
Three structures in prokaryotic cells that differentiate them from others
Plasmids, capsules and flagellum
Plasmids
Small loops of DNA that are separate from main circular DNA molecules
Contain genes which can be passed between prokaryotes
Capsule
Final outer layer of Prokaryotes (eg. Bacteria)
It helps protect bacteria from drying out and from attack by cells of the immune system of the host organism
Flagellum
Long,tail-like structures that rotate, enabling the prokaryote to move
Function of nucleolus
Produce and assemble the cells ribosomes
Nuclear envelope
separates the contents of the nucleus from the cytoplasm an provides the structural framework of the nucleus
Function of plasma membrane
Provides protection for the cell and provides a fixed environment inside the cell
