1.2 ultrasound of cells Flashcards
compare electron microscopes and light microscopes
electron have a much higher resolution that light
- resolution of fine features dependent on wavelength of light used
- lower wavelength, finer level of detail
- light microscopes constrained by wavelength of visible light [approx 400 – 700 nm]
- electrons have smaller wavelength [2 – 12 picometres, where 1 picom = 1 x 10^-12 m]
- light microscopes accurate to abt 1000x mag
- cellular components within organelles usually not resolvable using light micro [mitochondria can] but can be w electron micro
types of electron microscopes
scanning electron microscope
- electrons focused on surface of specimen to provide 3-dimensional image
transmission electron microscope
- electrons focused through sample; used to study internal structure of cells
what is the 3 domain system of biological classification
- archaea – “primitive” domain containing mainly microorganisms with unique properties [e.g. microorganisms found in deep sea vents, hot springs, or produce methane in anaerobic conditions, etc]
- bacteria
organisms under these 2 are considered prokaryotes - eukaryota [goes on to 4 kingdoms of protista, fungi, plantae and animalia]
cell structure of prokaryotes
- genetic material not encased within a membrane, coiled into region known as nucleoid
- unlike eukaryotic, do not contain any membrane-bound organelles
- cytoplasm encased within plasma membrane
- only 1 chromosome, in the form of circular dna
- may contain plasmids, accessorial extra-chromosomal dna that replicates independently from chromosome
- mesosomes may form from infolding of cell surface membrane to increase surface for activities like cellular respiration
- most bacteria feed via extracellular digestion, where enzymes are secreted out of cell and nutrients absorbed into cell, with all transport regulated by cell surface membrane
- many prokaryotes possess cell walls that maintain cell shape, and are commonly made up of peptidoglycans
- many prokaryotes possess slime layers that have some defense function and aids in formation of biofilms
how do prokaryotes divide? w elaboration
binary fission
- dna replicated in semi-conservative manner
- 2 dna loops attach to cell surface membrane
- cell surface membrane elongates and divides into 2 cells (cytokinesis)
- 2 daughter cells genetically identical
cell struture of eukaryotes
- dna encased within double membrane nuclear envelope
- cytoplasm found between nuclear membrane and cell surface membrane
- membrane bound organelles aid in compartmentalisation
let’s talk about nucleus [genetic control]
- largest and most visible organelle within cell
- storage location of genetic material in form of chromosomes (dna wound around histone proteins)
- nucleoplasm: material within nucleus
- encased within double membrane known as nuclear envelope
- presence of pores in nuclear envelope to regulate entry and exit of substances like mRNA
- nuclear membrane connected to system of membranes known as endoplasmic reticulum
- nucleolus: dense region within nucleus responsible for ribosomal rna production
- (summary) dna replication, rna synthesis, assembly of ribosomal subunits (in nucleoli)
let’s talk about ribosomes [genetic control]
- primarily involved in protein production / polypeptide synthesis
- made up of ribosomal rna produced in nucleolus of nucleus
- quantity of ribosomes found in cell dependent on amount of proteins that cell must produce
• Secretory cells that secretes hormones like the exocrine gland cells of the pancreas contains large numbers of ribosomes - either membrane bound or free floating
• Free ribosomes are found floating in the cytoplasm and are usually involved in the production of proteins needed within the cytoplasm
• Bound ribosomes are mainly found on the rough endoplasmic reticulum and are associated with proteins packaged in other organelles and exported out of the cell
what is the endomembrane system?
includes:
- nuclear envelope
- endoplasmic reticulum (er)
- golgi apparatus
- lysosomes
- vacuoles
- plasma membrane
let’s talk endoplasmic reticulum [manufacturing, distribution, and breakdown]
rough
- contains ribosomes (membrane bound) attached to membrane
- involved in production of polypeptides that usually will be transported via vesicles to the Golgi Apparatus for further packaging and subsequently exported out of the cell
- process: mrna goes through ribosome, codes for polypeptide, sugar chain attaches to form glycoprotein, transport protein buds / pinches off to carry secretory protein away
- (summary) synthesis of membrane lipids and proteins, secretory proteins, and hydrolytic enzymes; formation of transport vesicles
smooth
- lacks associated ribosomes
- involved in other metabolic processes including the production of enzymes necessary to produce lipids and steroids, or enzymes that processes drugs and alcohol
- (summary) lipid synthesis; detoxification in liver cells; calcium ion storage
let’s talk golgi apparatus [manufacturing, distribution, and breakdown]
- (summary) modification and sorting of macromolecules; formation of lysosomes and transport vesicles
- involved in further processing and packaging of molecular products of the cell
- folds and packages polypeptides together to form functional proteins
- molecular products travel via vesicles to one side of the Golgi apparatus
- products are processed, modified and processed as they travel to the other side of the Golgi apparatus
- vesicles containing the final products from the Golgi apparatus pinch off and travel to other organelles or the cell surface membrane for exocytosis
let’s talk lysosomes (in animal cells and some protists) [manufacturing, distribution, and breakdown]
- (summary) digestion of ingested food, bacteria, and a cell’s damaged organelles and macromolecules for recycling
- membrane bound sacs containing digestive enzymes
- originated from the Golgi apparatus, with the original polypeptides forming the enzymes produced in the rough ER
- presence of membrane helps to isolate the digestive enzymes from rest of the cell and cytoplasm to prevent auto-digestion (unless triggered to do so in some cells)
- needed for the digestion of food molecules in food vacuoles taken in via phagocytosis
- used to digest worn out organelles in the cell for nutrient recycling
- some can fuse with cell surface membrane to lead to exocytosis (secretion) of enzymes out of the cell
let’s talk vacuoles [manufacturing, distribution, and breakdown]
- large vesicles with a diverse range of functions
- contractile vacuoles are found in many protists that are able to mechanical pump out water for osmoregulation
- large central vacuole found in plant cells help in osmoregulation by buffering changes to water potential of plant cytoplasm
- food vacuoles are found in many cells to envelope food particles taken in via phagocytosis
- many plant cells contain vacuoles that store toxins or pigments
- (summary) digestion [food vacuole]; storage of chemicals and cell enlargement [central vacuole]; water balance [contractile vacuole]
what sets mitochondria and chloroplasts apart from the rest?
- double membrane
- not part of the cellular endomembrane system
- have own chromosomes (circular DNA)
let’s talk mitochondria [energy processing]
- found in almost all eukaryotic cells and are responsible for cellular respiration to produce energy in the form of Adenosine Tri-Phosphate (ATP)
- double membrane – smooth outer membrane and an inner membrane folded inwards to form cristae
- 2 compartments – mitochondrial matrix and intermembrane space
- mitochondrial matrix contains:
• enzymes that catalyse cellular respiration processes
• ribosomes
• mitochondrial DNA - folding of cristae increases surface area for reactions to occur that synthesizes ATP
- (summary) conversion of chemical energy in food to chemical energy of ATP
let’s talk chloroplasts (in plants and some protists) [energy processing]
- found in plants and are responsible for photosynthesis
- part of a class of organelles called the plastids
- double membrane system to form compartments
• Intermembrane space
• Stroma (contains enzymes, chloroplast DNA and ribosomes) - stroma contains an internal network of membranes arranged to form interconnected sacs known as thylakoids
• stacks of thylakoids form a granum and is rich in chlorophyll for photosynthesis - (summary) conversion of light energy to chemical energy of sugars
let’s talk cytoskeleton [structural support, movement, and communication between cells]
- made of three kinds of fibers:
• microfilaments (actin filaments) support the cell’s shape and are involved in motility
• intermediate filaments reinforce cell shape and anchor organelles
• microtubules (made of tubulin) give the cell rigidity and act as tracks for organelle movement - (summary) maintenance of cell shape; anchorage for organelles; movement of organelles within cells; cell movement [crawling, muscle contraction, bending of cilia and flagella]
let’s talk peroxisomes [manufacturing, distribution, and breakdown]
- organelle responsible for many oxidative reactions
- produces hydrogen peroxide and convert it to water
- oxygen is used to break down many substances
- bound by a single membrane
- (summary) diverse metabolic processes, with breakdown of toxic hydrogen peroxide by-product
[extra] let’s talk extracellular matrix [structural support, movement, and communication between cells]
- support, regulation of cellular activities
[extra] let’s talk cell junctions [structural support, movement, and communication between cells]
- communication between cells; binding of cells in tissues
let’s talk a little about cell walls (in plants, fungi, and some protists) [structural support, movement, and communication between cells]
- support and protection; binding of cells in tissues
compare prokaryotes and eukaryotes
SIZE
P: typically 0.2 – 2.0 microm in diameter
E: typically 10 – 100 microm in diameter
NUCLEUS
P: no nuclear membrane or nucleoli
E: true nucleus, consisting of nuclear membrane and nucleoli
MEMBRANE-ENCLOSED ORGANELLES
P: absent
E: present, e.g. lysosomes, golgi complex, er, mitochondria and chloroplasts
FLAGELLA
P: consist of 2 protein building blocks
E: complex; consist of multiple microtubules
GLYCOCALYX (glycoprotein and glycolipid covering that surrounds the cell membranes)
P: present as capsule or slime layer
E: present in some cells that lack cell wall
CELL WALL
P: usually present; chemically complex [typical bacterial cell wall includes peptidoglycan]
E: when present, chemically simple [includes cellulose and chitin]
PLASMA MEMBRANE
P: no carbohydrates and generally lacks sterols (steroid alcohols; a type of lipid)
E: sterols and carbohydrates that serve as receptors
CYTOPLASM
P: no cytoskeleton or cytoplasmic streaming (movement of cytoplasm in cell)
E: cytoskeleton; cytoplasmic streaming
RIBOSOMES
P: smaller size, 70S
E: bigger size, 80S; smaller size 70S in organelles
CHROMOSOMES (DNA)
P: usually single circular chromosome; typically lacks histones
E: multiple linear chromosomes with histones
CELL DIVISION
P: binary fission
E: involves mitosis
SEXUAL RECOMBINATION
P: none; transfer of dna only
E: involves meiosis
what are the benefits of compartmentalisation in eukaryotes?
- efficiency of metabolism – molecules kept close together to increase speed of reactions
- compartmentalised conditions – different organelles can be kept at different conditions (e.g. pH) for efficient reactions within a cell
- isolation of compounds – organelles like lysosomes can contain enzymes that needs to be isolated to prevent autodigestion, vesicles may isolate harmful toxins
- numbers – organelles can be kept in different numbers as per the needs of the cell
