Cell Structure and Ultrastructure Flashcards
define magnification
how many times bigger an object is compared to its actual size
define resolution
the distance by which 2 points must be seperated for them to be seen as 2 seperate points rather than a single fused image
limit of resolution for light and electron microscopes
“light- 200nm
electron- 1nm”
what does resolution depend on
”- wavelength of radiation (smaller the wavelength= higher resolution)
- numerical aperture of the lens”
Define the term “cell” in terms of its structure and function
Cells are the basic unit of life. They are small membrane-bound structures containing several smaller structures called organelles.
Explain the basic concepts of the cell theory
”- The structural and functional unit of living organisms is the cell.
- All living things are made up of cells.
- Cells originate exclusively by division of other cells.”
similarities between animal and plant cells
plasma membranes, mitochondria, SER, RER, nucleus, ribosomes, lysosomes, cytoplasm, microtubules, microfilaments
differences between animal and plant cells
“(plants)- cellulose cell wall, chloroplasts, plasmodesmata, permanent vacuole
(animals)- centrioles”
similarities between prokaryotes and eukaryotes
Similarities- both have cytoplasm, cell membrane (phospholipod bilayer)
differences between prokarotes vs eukaryotes
”- free circular dna vs coiled dna
- not associated with histones vs associated
- small ribosomes vs larger ribosomes
- bacterial cell wall (peptidoglycan) vs cellulose/… cell wall
-prokaryotes also have flagella, capsule and plasmid”
describe a light microscope
”- uses light waves
- can observe live specimen
- -relatively easy prep
- requires staining
- limited magnification and resolution
- x1500 mag
- 200nm resolution”
describe an electron microscope
”- uses beams of electrons - shorter wavelength than light
- higher resolution
- images in black and white
- expensive
- x500 000
- 0.5 nm resolution”
describe a TEM
”- Pass electrons through a specimen
- spec has to very thin
- stained with heavy metals
- spec needs to be dead
- dense regions appear darker”
describe a SEM
”- 3D images
- spec coated with thin layers of metals so scatters electrons
- not as powerful TEM in mag or res
- can magnify thicker specs”
describe the steps of cell fractionationation
“1. Homogenisation- homogenate cell in a blender to release organelles
2. in buffered (prevents organelles containing proteins denaturing), isotonic (prevents water moving into the organelles by osmosis- stops lysis) and ice cold (reduces the activity of enzymes that may break down the org)
3. filter to remove debris
4. suspension in centrifuged at a high speed, denser components form pellets at the bottom of the tube
5. supernatant spun again at a higher speed to turn the second densest into a pellet- repeat
6. nucleus, mitochondria/chloroplast”
advantages of being multicellular
- May have complex locomotion – not restricted by a particular environment
- Can grow to large sizes
- May develop NS to be aware of surroundings
- Obtain energy from a wide variety of foods
disadvantages of being multicellular
disadvantages
- Need for a specific transport system
- Reproduction often complex and slow
advantages of being unicellular
- No need for a transport system diffusion adequate
- Reproduction is simple and rapid
- Change and evolve more rapidly to adapt to the environment
disadvantages of being unicellular
- Often limited by the environment (and resources within it)
- Limited by size due to diffusion
define differentiation
a natural process where a cell with less specificity develops and matures to become more distinct in terms of form and function. becomes a specialised cell.
define specialisation
specialised cells are adapted structurally and biochemically to perform a particular function
define stem cell
they are unspecialised cells that can reproduce for a large number of generations and under appropriate conditions differentiate into specialised cells
what are 2 types of stem cells
“adult
embryonic”
describe embryonic stem cells
”- divide and differentiate into specialised embryonic tissues. i
- in the early embryo - totipotent but from the inner mass of a blastocyst, they are pluripotent”
describe adult stem cells
”- Multipotent
- Constant renewal of adult stem cells
- These stem cells are involved in repair and replacement of specialised cells e.g skin, blood, muscle”
hows does differentiation occur
“Determination-
- the initial change in the stem cell happens at the molecular level so the cell still looks the same
- determines what genes will be switched on/off for TSP (tissue-specific proteins)
- TSP determines the structure and function of genes so that cells can be structurally and biochemically specialised”
what is determination controlled by
”- Cytoplasmic determinants
- Induction”
what is induction
”- the process by which cells within the early embryo produce and release chemicals that signal nearby cells to change their gene expression.
- More frequent/significant cause of differentiation than cytoplasmic determinants”
what is organisation
”- way in which specialised cells are grouped together to form tissues, organs and organ systems within the body
- Occurs within the developing embryo
- essential for multicellular orgs to function effectively”
steps to organisation
“occurs after stem cells divide in developing embryo to differenciate depending on cytoplasmic determinants and inductio.
1.The axis of the embryo are developed.
2.Then segmentation occurs dividing the embryo into specific areas.
3.Apoptosis (cell death) is also involved in this process”
what is axis establishment
determines which end of the embryo is which
def of cranial, caudal, dorsal, ventral
“cranial- front
caudal- behind
dorsal- top
ventral- under”
what is segmentation
”- the (cytoplasmic determinant) proteins which determine egg polarity affect the embryo’s genes
- Different concentrations of these proteins lead to a difference in gene expression of other genes involved in segmentation
- products of segmentation genes determine the formation of different segments within the embryo after the major axes have been determined”
why is apoptosis important
”- cell death
- Embryogenesis requires both cell division and controlled cell death for the correct development of body systems, e.g.. Morphogenesis of feet and paws- Webbed feet occur due to a lower apoptosis rate”
name the different germ layers and name the bodily tissue it forms
“Ectoderm- outer external- epidermis/ hair/ nails/ brain
Mesoderm- middle- muscle, bone, connective tissue, kidney
Endoderm- within- stomach, colon, liver, pancreas”
what are the four classes of animal tissue
”- Epithelial tissue
- Nervous tissue
- Connective tissue
- Muscle tissue.”
describe the function of epithelial tissue
”- forms a lining for many structures.
- Can be protective
- Adapted for absorption, secretion, excretion
- Has a basement membrane
- single layer = simple epithelium
- several layers = stratified epithelium”
name the 5 types of epithelial tissue
- simple squamous epithelium
- Simple cuboidal epithelium-
- Simple columnar epithelium-
- Ciliated columnar epithelium-
- Stratified epithelium
decribe the structure of the simple squamous epithelium
thin flat cells with flattened nucleus (lining of alveoli)
decribe the structure of the simple cuboidal epithelium
Cube shaped cells with a central spherical nucleus. E.g. the cells lining the kidney tubules
decribe the structure of the simple columnar epithelium
elongated or column shaped, the nucleus is usually found at the base
decribe the structure of the ciliated columnar epithelium
similar shape to simple columnar epithelium but also have cilia on their surface. (lungs, cilia moves mucus along)
decribe the structure of the stratified epithelium
several layers of cells and so provides more protection, top layer of cells becomes flattened and scaly and may be keratinised (skin/ lining of reproductive tract)
what are the 2 types of nervous cells
Glial cells-
Nuerones
whats the function of glial cells
- Protection against disease.
- Supplying nutrients from the blood to the neurones.
- Maintaining the correct balance of ions in the tissue fluid surrounding the neurones.
- Production of the insulating myelin sheath by specialised glial cells known as Schwann cells.
whats the functio of neurones
- transmit information around the body in the form of action potentials, which are also called nerve impulses.
function of connective tissues
”- binds structures together
- made up of cells and an intercellular matrix
- found throughout the body
- support, protection and repair.”
What are the 4 types of connective tissue
- Bone tissue
- Cartilage
- blood
- fibrous
Describe bone tissue
- Made up of cells within a matrix.
- two types, Compact bone and Spongy bone
- constantly re-modelled through life
- hard because of calcium phosphate in the extracellular matrix.
Describe blood tissue
liquid tissue
describe cartilage tissue
- cells called chondrocytes
- produce a matrix which is made up of collagen, glycoproteins and water.
- Unlike bone, cartilage does not contain calcium phosphate and it is therefore more flexible than bone
- continually broken down and renewed throughout life, just like bone.
Describe fibrous tissue (dense/loose)
- contains fibroblast cells and an extracellular matrix
- either dense or loose depending on how many fibres are present in the matrix
- fibres can be collagen (tendons/ ligaments) or elastin (aorta wall)
DENSE
- higher proportion of fibres
- fewer cells
LOOSE-
- less fibres and more cells
- less rigid and more easily distorted
- but due to the presence of collagen, it can still provide resistance when stretched creating a tough barrier.
- eg. adipose tissue / the mesentery
