EUKARYOTIC CELL STRUCTURE AND FUNCTION 🧫

Question 1

Cell theory in one line, and the broken down version

Answer 1

Cell theory states that cells are the fundamental unit of structure, function and organisation of all living organisms and new cells are only formed from other exisiting cells

1. All living organisms are composed of one or more cells
2. Cell is the most basic unit of structure in all organisms
3. All cells only arise from pre-existing cells

Question 2

Differences between prokaryotic and eukaryotic cells

7 points

Answer 2

Size: Prokarytoic cell smaller than eukayotic cell

Nucleus:
Prokaryotic: no true nucleus
Eukaryotes: has a true nucleus

Membrane bound organelles:
Prokaryotes: absent
Eukaryotes: present

Plama membrane:
Prokarypotes: contain no carbohydrates and usually sterols
Eukaryotes: contains carbohydrates and sterols that usually act as receptoss

Cystoplasm:
Prokaryotes: no cytoskeleton and cytoplasmic streaming
Eukaryotes: contains cytoskeleton and cytoplasmic steaming

DNA:
Prokaryotes: circular and wound around histone-like protein
Eukaryotes: linear and wound around histone protein

Cell division:
Prokaryotes: binary fission
Eukaryotes: mitosis

Question 3

Functions of cells

Answer 3

Movement.Excretion.Reproduction.Respiration.Irritation.Nutrient.Growth

1. Intake of raw materials
2. Extraction of useful energy from raw materials to synthesise it own molecules
3. Growth in an organised manner
4. Respond and adapted to changes in the external environment

Question 4

Lower limit and upper limit of a cell

Answer 4

Lower limit: minimum amount of space required to contain essential elements of its function

Upper limit: determined by surface area:volume ratio of cell needed for exchange of materials between cell and extracellular environment

As size of cell increases, surface area of volume of cell decreases. Number of chemical exchanges that can take place between cell and extracellular environment inadequate to maintain cell. As cytoplasm is far away from outer membrane, exchange with cellular environment is vital as substances like oxygen and nutrients can only enter the cells, and waste can only exit the cell, i this fashion

Question 5

Non-membranous organelles

6

Answer 5

Cytoskeleton, centrioles, centrosomes, ribosomes, cillia, flagella

Question 6

Membranous organelles

6

Answer 6

mitochondria, chloroplast, nucleus, endoplasmic reticulum, golgi body, peroxisomes

Question 7

Double membraned organelles in cell

Answer 7

mitochondria, chloroplast, nucleus

Question 8

Define a cytoskeleton

Answer 8

network of fine strands of globular and fibrous proteins that provide infrastructure and support to cell

Question 9

Components of cytoplasm

Answer 9

1. essential ions and soluble organic molecules
2. soluble proteins
3. cytoskeleton

Question 10

Advantage of having membranous organelles

Answer 10

1. allow for maintenance of characteristic differences between cytosol and contents of organelle. compartmentalisation of specific cellular reactions provide different local environment in which incompatible cellular processes can occur simultaneously, increasing efficiency of cell
2. increase membrane surface area: enzymes and proteins that mediate cellular processes embedded in membrane. larger the membrane suface of area, larger the number of enzyme complexes that can be embedded, increasing efficiency of many reactions by providing optimal enzyme concentration for reaction to occur
3. contain harmful substances in organelles

Question 11

Nucleus

Answer 11

Characteristics:
1. largest organelle in animal cell, can be seen under light microscope
2. encloses genetic material
3. protects DNA from metabolically active cytoplasm
4. Double membrane, nuclear envelope is perforated to allow for exchange of substances between nucleus and cytplasm

Nuclear envelope:
1. double membrane
2. functions to separate contents of nucleus from ctyoplasm
3. outer membrane continous with membrane of ER
4. space between outer membrane and inner membrane known as perinucleus space and is continuos with lumen of ER
5. perforated by nuclear pores which is a large protein complex to allow for macromolecules such as mRNA and rRNA to exit the nucleus, and proteins such as enzymes and to enter and exit the nucleus

Nucleoplasm:
1. aqueous matrix consisting of ions, proteins, metabolites, chromatin and RNA
2. chromatin wound around histones and exist in:
- euchromatin form: chromatin loosely coiled aroud histones, seen as light patches
- heterochromatin: tightly coiled around histones, inactive, seen as dark patches

Nucleolus:
1. contains DNA carrying rRNA genes, RNA and proteins
2. functions to synthesise rRNA which is a component of ribosomes

Question 12

Forms of genetic material in nucleus + how their seen under the microscope

Answer 12

Euchromatin - light patches
Heterochromatin - dark patches

Question 13

Components of endomembrane system, importance and functions

Answer 13

1. rER and sER
2. golgi body
3. vesicles
4. lysosymes

important in intracellular division of labour. compartmentalisation and therefore allow for efficiency through locations of multi-enzyme pathways

Question 14

Endoplasmic reticulum structure + function

Answer 14

ER: extensive network of hollow, membranous tubules, sheets or sacs known as cisternae

Adaptations:
1. extensive network of cisternae increases surface area of ER for synthesis of subtances
2. hollow cisternae accomodates the synthesis of new substances and packaging into vesicles for transport to GA

rER:
1. sheet like, rough appearance due to ribosomes that stud ctyosolic face of rER
- Function:
1. at rER bound ribsomomes, site of protein synthesis where polypeptide chains are synthesised
2. newly synthesised polypetide chain enters rER lumen which is the site of protein folding, through protein channel in rER membrane polypeptide chain is folded into its native conformation
3. destined for excretion or are targetted to cellular organelles

Significance:
1. cells active in protein secretion have an adunance of rER
2. some protein synthesised in rER can directly enter membrane of ER and act as ER membrane protein
3. protein that leave rER are enclosed by vesicles known as transport vesicles

sER:
1. smooth network of tubules with no ribosomes bound to its surface, hence its smooth appearance
2. carry out many metabolic functions:
- synthesis of lipids, abundant in cells that function to secrete hormones
- metabolism of carbohydrates
- detoxification of poisons and drugs
- storage of calcium ions which is used in muscle contration and cell to cell signalling

Question 15

Golgi apparatus:
- function
- structure

Answer 15

Function: modification and packaging of ER products
Structure:
- flattened, membrane bound sacks called cisternae
- distinct polarity of cis face(forming face) and trans face(mature face)

Function: transport vesicle, secretory vesicle, lysosyme, golgi vesicles
- at cis face, new cisternae form by receiving transport vesicles from ER. membrane of transport vesicles fuse with cis face and deposits its contents into Golgi cisternae space
- at trans face, membrane buds off to form secretory vesicles and its contents are transported to extracellular matrix
- membrane at trans face of golgi body can also bud off to form lysosymes
- between golgi sacs, golgi vesicles function to transport materials between different parts of the golgi
- golgi vesicles bud off from trans face to transport materials to other organelles in the cell

Function:
modification of ER products include glycosylation, addition of sugar groups, trimming, removal of monomers. different golgi cisternaes contain different enzymes for modficiation, ER product is progressively modified as it moves through the stacks of golgi complex from cis face to trans face
- processed and packaged contents are then passed onto other components of cells by secretory vesicles that bud off from GA

Significance:
1. cells that are active in any form of secretion usually have abundant GA as GA has abundant flattened cisternae which increase surface area for budding and reception of vesicles
2. multiple cisternae allow for many modificiation processes to occur simultaneously

Question 16

Lysosymes structure + 3 major functions

Answer 16

Structure: membranous organelle that appears homogenously electron dense under EM
- due to acidic nature of its contents and hydrolytic activity of its enzymes, spilling of lysosymal contents into cytosol must be prevented
- segregation of lysosomal content from cytosol by membrane is essential to maintain optimum pH for hydrolytic activity and prevent hydrolysis of other cellular content

Function:
1. Digestion of materials taken into cell:
- food taken into cell by endocytosis to form food vacoules, fuses with lysosymes to form endosomes. enzymes can digest the endosome’s contents which end up in cytosol to be used as food by the cell
- same thing can happen for bacteria taken into the cells as a defense mechanism, fuses with lysosymes to for phagosome
2. Autophagy:
- worn out cellular organelles enclosed by membrane of unknown origin to form a vesicle, vesicle fuses with lysosyme to form autophagic vacuole
3. Autolysis:
- apoptosis where cell self-destruct in a controlled, programmed manner. when organism undergo development of differentation, or when cell senses it has become a threat to surrounding
- autolysis occurs when there is a mass release of lysosymal contents in whole cell

Question 17

Vacuole structure + function in plant cells and animal cells respectively

Answer 17

In general, vacuoles bud off from ER and GA, considered part of endomembrane system

Animals cells:
- small, mobile organelles
- function to house and transport substances

Plant cells:
- large central vacoule enclosed by membrane known as tonoplast, and contents of tonolplast known as cell sap
- functions:
1. storage of organic compounds and inorganic ions
2. disposal site of toxic metabolic by-product
3. contains colour pigments
4. protects plant by accumulating compounds that are toxic and unplatable for consumers
5. along for growth and elongation of plant cell: increase in size of vacuole by water molecules accumulating in vacuole. allow for increase in size of plant cell with minimal investment in cytoplasmic synthesis and without sacrificing surface area to volume ratio of plant cell as cytoplasmic content is pushed to peripheary of cell

Question 18

Mitochondria structure + function

Answer 18

Structure: spherical and elongated

Function: Site of aerobic respiration, catabolic process wehre ATP is generated through the extraction of energy from sugars, fats and other metabolic fuels in the presence of oxygen

Function in relation to structure:
1. double membrane, narrow fluid filled space between inner and outer membrane known as inter-membrane space
- outer membrane is smooth while inner membrane is highly convoluted, increase surface area for attachment of various enzyme systems involved in aerobic respiration
2. mitochondrial matrix enclosed by inner membrane, mitochondrial matrix contains enzymes, RNA, circular DNA, ribomsomes so mitochondria can synthesise its own proteins + is the site of the krebs cycle
3. compartmentalisation is also necessary to set up proton gradient across inner mitochondrial membrane as inner mitochondrial membrane is impermeable to protons

Question 19

Chloroplast structure + function

Answer 19

General function:
- site of photosynthesis where light energy is converted to chemical to drive the formation of organic compounds from water and carbon dioxide
- carry out photosynthesis for the synthesis of organic compounds
- chloroplast asbord light to synthesis ATP and NADPH during light-dependent reactions used in the Calvin Cycle

Strucutre:
1. lens-shaped
2. bound by double membrane known as chloroplast envelope

Structure in relation to function:
Stroma - inner membrane encloses the stroma which is a semi-fluid matrix
1. contains circular DNA for synthesis of chloroplast proteins
2. excess sugar synthesised during photosynthesis coverted to starch and stored as starch grains in the stroma
3. stroma is the site of light-independent reactions of photosynthesis and contains enzymes requried for those reactions to take place

Thylakoid - membrane enclosing the thylakoid lumen
1. thylakoid lumen + thylakoid = thylakoid disc
2. thylakoid discs stack up to form a grana
3. connected stacks of grana are connected by sheet-liked thylakoids known as intergrana lamellae
4. thylakoids are the site of light-dependent reactions of photosynthesis. increase membrane area for the attachment of chlorophyll and othe photosynthetic pigments
5. compartmentalisation allows for set up of proton gradient across inner chloroplast membrane as inner membrane is impermeable to protons

Question 20

Differences and similarities of mitochondria and chloroplasts

Answer 20

Similarities:
1. both are energy transducers which convert energy to forms that can be used by the cell
2. both are bound by a double membrane
3. both contain circular DNA
4. both contains ribosomes

Differences:
1. chloroplast is only present in plant cells
2. chloroplast is visible under light microscope while mitochondria is not
3.

Question 21

Ribosome structure + function

Answer 21

General function: synthesis of proteins

Structure: 2 subunits, large ribosmal subunit and small ribosomal subunit which are made up of proteins and ribosomal RNA
- eukaryotes: 80s ribomsomes
- prokaryotes: 70s ribosomes

Location:
- attached to rER(80s)
- floating freely in cytosol(80s)
- in mitochondrial matrix(70s)
- in chloroplast stroma(70s)

Function:
- ribosomes attached to rER and known as bound ribosomes and protein it synthesises are destined to:
1. to be exported
2. to be inserted into membrane
3. targetted at various membrane-bound organelles

• ribsomes in cytosol are known as free ribosomes, protein it synthesies:
  1. stay within the cell
  2. and function in the cytosol or in the nucleus

Question 22

Cytoskeleton structure + function

Answer 22

Structure: 3D array of interconnected tubules and filaments
- consists of microtubules, microfilaments and intermediate filaments

Functions:
1. provide mechanical support to cell and shape to the cell
2. provides anchorage and direction to movement of organelles and molecules within the cell
3. provides cell motility
- microtubules: provides structural support. specialised arrangements of microtubules arise from microtubule organising centres, which gives anchorage and orientation to microtubule assembly. microtubules also involved in the transport of molecules from one part of the cell to another
- microfilaments: involved in the movement of the cell and changes in cell shape.
- intermediate filaments: helps stabilise organelles and involved in specialised cell junctions

Question 23

Centriole structure + function

Answer 23

Location: found near nucleus in region known as centrosome which is rich in specific protein for microtubule assembly

Structure: centrioles come in pairs, arranged at right angles to each other. each consists of nine triplets of microtubules arranged in a ring

Function: during cell division, each centriole replicates itself and move to opposite ends of the cell. centrosome act as microtubule organising centre for the formation of spindle fibres involved in nuclear division

Question 24

Plant cell wall structure + function

Answer 24

Structure:
1. highly rigid
2. consists mainly of structural polysaccacharide cellulose
3. region between cell walls of adjacent cells is known as middle lamellae, region rich in polysacchardies such as pectin that helps adjacent plant cells adhere together

Function:
1. supports and determins shape of plant cell
2. protects plant cell from mechnical injury and invasion
3. high tensile strength allows cell to withstand high hydrostatic pressure exerted by entry of water molecules into cell and prevents execessive uptake of water molecules by cell

Question 25

Difference between plant cells and animal cells

Answer 25

Cell wall: Plant: present Animal: absent Centriole: Plant: absent Animal: present Chloroplast Vacuole

Question 26

LM vs EM

Answer 26

Working principle: LM: visible light EM: electron beams Magnification: number of time larger image is to specimen EM higher than that of LM Resolution: shortest distance between 2 points that can be distinguised by the viewer - inversely proportional to wave length of radiation being used - EM has higher resolving power than LM as electron beam has shorter wave length than LM Ability in contrast: amount of colour or grayscale differentation between 2 images Lens: LM: glass EM: electromagnets Environment: LM: no vaumn needed EM: vacumn necessary Stain: LM: colour dyes - methylene blue: nuclei stained blue - safrnin/light green(for plant cells): cytoplasm and cellulose green, nuclei and lignin red, chloroplast pink - haemotoxylin/eosin: nuclei stained blue, cytoplasm stained pink EM: stain containing heavy metal ions to reflect electrons Specimen: LM: living or non-living EM: non-living - specimen used for EM is usually in thinner sections for penetration of electrons, so details of cell can be seen - specimen is destroyed at the end due to bombardment by electrons - unable to survive staining by toxic heavy metal stains and high vacumn required - EM cannot allow for view of biological processes in real-time Colour: LM: usually coloured EM: black and white(image formed by the detection of electrons passing through specimen) Capturing of image: LM: eye/photgraphic film EM: software to view image/use of photographic film

Question 27

Cell Fractioning - homogenisation and differential centrifugation

Answer 27

studies of isolated organelles, used to separate out a homogenous population of subcellular organelles from cytoplasm of cell as a whole Homogenisation: disruption of cell and release of invidual cellular components: - Mechanical methods: 1. motar, pestle and abrasive material 2. homogeniser/blender 3. pressure cell 4. ultrasound 5. osomtic lysis via use of hyperosmotic homogenisation medium to rupture protoplast - Chemical dissolving of phospholipids in membrane using detergents - To protect integrity of cellular organelles 1. use of isotonic medium containing sucrose, mannitol, sorbitol 2. buffer solution to maintain suitable pH 3. keep temperature to 4°C to inhibit protease activity Differential centrifugation: isolation/separation of cellular components Method: homogenate subject to progressively higher speeds and longer durations of centrifugation, separating particles in descending size and density Principle: size, shape and density of organelle affects it sedimentation coefficient + most intracellular organelles are discrete molecules with unqiue sizes and densities - faster the rotation, the greater the gravitational force generated and smaller the particles that will sedimented - after each speed, supernatant is drawn off and can be re-centrifuged at higher speed and longer duration - series of pellets collected containing cell organelles that are smaller and smaller

Question 28

Autoradiography purpose + methodology

Answer 28

Definition: use of x-ray films to visualise molecules or fragments of molecule that have been radioactively labelled/detect DNA fragments after separation by gel electrophoresis Purpose: - identification of site of synthesis and cellular distribution of metabolic products by tagging specific specimen molecules with radioisotopes - use of LM or EM to trace secretion products and their intermediates from their synthesis sites, through cellular organelles, to their eventual destinations Method: 1. cells or tissues incubated with radioactive substances 2. after radioactive substance has been taken up, sample mounted on glass slide dipped in photographic emulsion. as radioactive isoptoes decay, darks spots are formed on the photographic emulsion, allowing for identification of the radioactive substance