Unit 2 Topic 3A Cell structures Flashcards
How to identify an eukaryotic cell by microscope?
Features that only eukaryotic cells have:
- True nucleus
- Membrane-bound organelles
+ Size (usually larger than prokaryotic but cannot use to identify)
Describe nucleus in eukaryotic cells
- have double membrane
- have nuclear membrane / nuclear envelope ==> DNA in chromosomes are bounded inside nuclear envelope
Cell walls of prokaryotic cells
- some have peptidoglycan cell walls
- some have cellulose cell walls
Define cell fractionation
Process to break cells apart and separate cellular components of different sizes to isolate some organelles
State the significance of a cell consisting of different membrane-bound organelles
- incompatible chemical reactions can take placce in the same cell
- membranes separate compartments: biological molecules (ie. enzymes) and other necessary conditions (ie. pH)
- are available in different compartments for specific reactions
What are the main functions of nucleus
- control cellular activities: by the formation of mRNA to control gene expression in protein production
- nucleolus: synthesis of ribosomes
- nuclear pores: facilitate exchange of substances between nucleus and cytoplasm (exit of mRNA)
- stores genetic information
- control cell division
- controls metabolic reactions
What are the main properties of nucleus
- double membrane bounded structure: phospholipids in phospholipid bilayer, 4 layers of phospholipids
- nucleolus: site of synthesis of ribosomes
- outer membrane of the nuclear envelope is continuous with rough endoplasmic reticulum
- cell cycle (chromosomes: long, thin, invisible chromatins that disperse during interphase, condensed, shorter, thicker during cell division)
State the main functions of mitochondrion
site of aerobic respiration by converting energy in food to energy the cell can use
State and describe the properties of mitochondrion
- rod shaped
- double membrane bound
- too small to be seen under light microscope
Describe the inner membrane of mitochondrion
- highly folded to form tubular processes: cristae
- convered with stalked particles (ATP synthase)
- contains electron carrier molecules forming the electron transport chain involved in aerobic respiration
- space enclosed by inner membrane: matrix
What is mitochondrial matrix?
- fluid which contains enzymes for Krebs cycle
- contains mitochondrial DNA and mitochondrial ribosomes
Describe the intermembrane of mitochondrion
fluid-filled
Describe the outer membrane of mitochondrion
smooth boundary of the rod-shaped mitochondria
Applications of mitochondrion
- sperms have lots of mitochondria in the middle part of the tail (provides energy for swimming)
- liver cells (high level of metabolic activities,** requires lot of energy**, large number of mitochondria to meet energy requirement)
- enzyme-secreting cells (synthesis of enzymes/exocytosis require energy)
- epithelial cell in small intestine and root hair cells: absorption of nutrients and minerals
cells with higher metabolic rate contains larger number of mitochondria
Main functions of centrioles
- maintain shape and provide support to cells
- produce spindle fibres consisting of microtubules to
- guide movements of chromosomes during cell division
- for the movement of the organelles (exocytosis vesicles are made rom spindle fibres produced by centrioles to guide movements)
Properties of centrioles
- found in animal cells only
- hollow cylinders each consisting a bundle of 9 sets of 3 microtubules arranged in a ring
Main function of ribosomes
site for protein synthesis
Properties of ribosomes
- 80s ribosomes: exist on rER and freely suspended in cytoplasm in eukaryotic cells
- 70s ribosomes: exist in mitochondria and chloroplasts and prokaryotic cells
- consists of 2 subunits (each made up of proteins and RNA)
Main functions of lysosomes
- digest other organelles by fusing with them: autophagy
- destroy old cells
- digestion of materials engulfed by the cell
Explain the process of autophagy
- Sequestration: autophagosome is formed around cytoplasm and organelles
- Transport to lysosomes: fuse with lysosomes
- Degradation: lysosomes release enzymes to degrade material in autophagosome
- All cellular materials degrade to amino acids, retired to cytosol for reuse
(not in syllabus? but useful)
Explain how lysosomes destroy old cells
Apoptosis
1. rupture and release hydrolytic enzymes (protease, nucleases, lipas, gluosidases)
2. destroy old cells in programmed destruction of cells
Example: destroy cells in the tail of tadpole to develop into a frog
Explain how lysosomes can carry out digestion of materials engulfed by the cell
- food particle engulfed into the cell by phagocytosis and form a phagosome due to the fluid mosaic property of the cell membrane (vesicle formed around the food particle)
- lysosome fuses with phagocytic vacuole
- lysosymes in the lysosome digest bacteria / other cells / macromolecules engulfed
Properties of lysosomes
- contian hydrolytic enzymes: lysozymes (involved in intracellular digestion)
- formed by **breaking off from Golgi apparatus **
Main function of Rough endoplasmic reticulum
synthesis and transport of protein
Properties of Rough ER
- cisternae: stack of flattened membranous scas
- 80S ribosomes attached on surface
- space between rER is continuous with the space between the outer and inner membrane of the nucleus
- assists with protein synthesis
Explain the role of rough ER in protein synthesis
- protein synthesised at 80S ribosomes on the rER
- move into the rER: polypeptides folded to form 3D conformation
- proteins packaged into vesicles -> pinched off at the end of the rER
- vesicles containing protein move and fuse with Golgi apparatus, where proteins are modified
Main function of the smooth ER
synthesis, transport and storage of lipids
Properties of the smooth ER
- no ribosomes attached on the surface
- a network of interconnected membrane-bounded sacs: large surface area for enzymes to attach and carry out reactions
- abundant in cells that produce a large amount of lipids
Main function of the Golgi apparatus
- modification of protein (addition of prosthetic group to produce conjugated proteins)
- packaging of proteins by producing secretory vesicles (receiving vesicles from rER, sER)
Properties of Golgi apparatus
- cisternae: stack of flattened membranous sacs
- surrounded by secretory vescicles pinched off from the Golgi apparatus
Elaborate and describe the relationship of Golgi apparatus and proteins
- proteins are modified (addition of carbohydrates through glycosylation to produce glycoprotein / activation of enzymes)
- modified proteins are packaged into secretory vesicles ==> pinched off from the Golgi apparatus
- move towards and fuse with cell surface membrane ==> release proteins outside the cell by exocytosis
What to cytoskeleton do
- strengthening and support the cell’s shape and holding organelles in place
- intracellular movement: movement of organeles
- cellular movement: movement of cilia and flagella
- changing shape of cell during endocytosis, exocytosis, phagocytosis
Properties of cytoskeleton
- made up of microtubules and microfilaments (and centrioles)
- extensive network of protein fibres
- provides pathway for vesicles to move along microtubule using ATP
Describe the role of both Golgi apparatus and rER in the formation of enzymes
- polypeptide moves into the lumen of rER to be folded into 3-d shape
- enzyme packaged into vescicle ==> transport to golgi apparatus
- modified enzymes by adding carbohydrate
- leave the cell by exocytosis
What do nucleus contain
- nucleolus (tiny rounded deeply stained strucutre)
- genetic material
- DNA coiled around histone protein
- if cell is not dividing, genetic material appears as dispersed islands
- if cell is dividing, genetic material appears as thread-like strucutres
Differences between two types of endoplasmic reticulum
rER
- covered by ribosomes
- synthesis and transport of proteins
- formation of Golgi body
sER
- not covered by ribosomes
- synthess and transport of lipids
Describe how insulin is formed and secreted from the cells of pancreas
- ribosomes on rER are reponsible for formation of primary protein structure
- folding into tertiary strucutre takes place inside rER
- modification of proteins take place inside Golgi apparatus
- modified protein (insulin) is packaged in secretary vesicles that pinch off the maturing surface and move towards the cell membrane to be exocytosed
State the comparison between ER and Golgi body
Similarity
- both are single membrane bound
Differences
- ER has interconnected sacs while Golgi body is stack-like collection of sacs
- only ER may be covered by ribosomes
- Golgi body => forming surface and maturing surface
Comparison of 80S ribosomes and 70S ribosomes
80S
- larger
- outer nuclear membrane
- rER
- free in cytoplasm
70S
- smaller
- bacterial cells
- inside mitochondrion
- inside chloroplasts
What is in the mitochondrion matrix
- DNA loops
- 70S ribosomes
- Enzymes
- Phosphate granules
Name the organelles that are surrounded by double membranes
- chloroplasts
- mitochondria
- nuclei
Compare the structure of rER with the structure of sER (2)
- both consist of membrane bound sacs called cisternae
- in both organelles, cisternae are interconnected
- rER has 80S ribosomes while sER does not
Main functions of cell wall
- provides protection to the cell, prevents physical damage
- provides structure to the cell
- prevents from osmotic bursting
Properties of cell wall
- consists of middle lamella, primary cell wall, secondary cell wall, plasmodesmata
- no lipid bilayer, fully permeable
Properties of the middle lamella
- consists of mainly pectin / calcium pectate
- gel-like substance that allows plant cells to stick together
- lies between and holds together the primary cell walls of two adjoining plant cells
Properties of the primary cell wall
- mainly composed of cellulose
- unbranched, straight polymer of β-glucose, joined by 1-4-glycosidic bonds by condensation
Define microfibrils
units of parallel cellulose moleclues held together by hydrogen bonds
- cellulose molecules are unbranched and in straight chain
- connected by hemicelluose and embedded in pectin
- flexible and extend during growth of plant cells
- criss-cross at different angles ==> mesh structure
Properties of secondary cell wall
- mainly composed of cellulose
- may also consist of hemicellulose and lignin
Define hemicellulose
- polymer made up of different types of sugar units, such as galactose, mannose, xyrose
Define lignin and its function
- complex organic polymer that is impermeable to water
- thickens and hardens cell wall
- stop further growth of plant cell
- only in secondary cell wall
Why are cellulose molecules in cellulose microfibrils parallel
- flexibility
Why are microfibrils arranged into a mesh strucutre in primary cell wall?
high tensile strength and rigidity
Define plasmodesmata and state its function
- cytoplasmic bridges through pores in cell walls of adjacent plant cells
- routes for signalling substances (intercellular communication) to pass from ctyoplasm of one cell to another
- more permeable than pits
Define and state the properties of pits
- areas around plasmodesmata with unthickened cell wall
- water moves between cells through pits
Compare the structure of primary cell wall and secondary cell wall
- both contains cellulose microfibrils
- both embedded in pectin + hemicellulose
- secondary contains lignin while primary does not
- microfibrils in primary cell wall orientated in **different directions **for each layer
- microfibrils in secondary cell wall are oriented in same direction for each layer
describe the structure of cellulose in plant cell walls (2)
- cellulose in an unbranched polymer of beta-glucose joined by 1,4-glycosidic bonds
- cellulose molecules linked by hydrogen bonds forming microfibrils, which are arranged in layer
Describe the structure of plant cell wall
- cellulose molecules lie parallel with each other
- celullose molecules joined by hydrogen bonds to form microfibrils
- layers of microfibrils criss-cross with each other forming a matrix
- the middle lamella holds the cell wall of 2 adjoining plant cells
- lignin in secondary cell walls thickens and hardens cell wall
State the main functionsof vacuoles
- enables growing plants to elongate by stretching
- cell sap store organic substances
- contractile vacuole involved in regulation of water content and waste removal (maintains osmotic balance)
Why is the size of vacuoles in plant cells larger than in animal cells?
- animals don’t need to store as much water
- plant needs vacuoles to maintain water balance
State the differences of vacuoles in mature plant cells and immature plant cells
mature plant cells: large central vacuole
immature plant cells: many small vacuole, absorbs water: elongate and increase turgor pressure
What is vacuoles enclosed by?
membrane called tonoplast
Functions of cell cap in vacuoles
- store organic substances
- such as sugar, amino acids, inorganic ions, metabolic waste and pigments
What are contractile vacuoles invovled in?
-regulation of water content and waste removal in some protozoans and unicellular algae
- absorbs water from cytoplasm and pumps water out of a cell
- important adaption to survive in hypotonic condition (net movement of water into cell, vacuole removes excess water)
Major function of chloroplast
- contains chlorophyll which converts light energy to chemical energy by photosynthesis
What are the properties and shape of chloroplast
- double-membrane bounded
- biconvex shape
- loop of DNA (circular)
- 70S ribosomes present
Define chlorophyll
- pigment in chloroplast on thylakoid
What does stroma contain and what is the function?
- jelly-like fluid
- contain enzymes needed for carbon fixation (site of dark reaction of photosynthesis)
What are the three components of the chloroplast envelope?
- outer membrane
- inner membrane
- intermembrane space
Define and state the properties of thylakoid
- flattened membranous sac
- membrane: thylakoid membrane (chlorophyll molecules on membrane)
- disk shape
- piled up into a stack: granum
define integranal lamella
- extention of thylakoid membranes connecting grana
- entire flattened sac: intergranal thylakoid)
what stores starch in chloroplast
- starch grains / amyloplast / starch ganules
- embrane bound
- insoluble in the stroma
Why are there amyloplast to store glucose in chloroplast?
- some glucose produced during photosynthesis is converted to starch
- temporarily stored in chloroplast
State properties for prokaryotic cells
- unicellular (organism made up of one cells)
- no true nucleus (DNA floating freely in cytoplasm, concentrated in nucleoid)
- no membrane-bound organelles
- peptidoglycan cell wall
- include mesosomes
- 70S ribosomes in cytoplasm
State the properties of cell wall of a bacetrial chromosome
- peptidoglycan (protein and carbohydrates) cell wall
Main functions of slime layers and capsules
- prevent dehydration of cells
- protect pathogenic (disease causing) bacteria from antibodies / phagocytes / antibiotics and in the hosts’ immune system
- some bacteria may attach on host cells with the capsule or slime layer
Define phagocytes
type of blood cell which engulf pathogens by phagocytosis
Properties of slime layers and capsules
- around cell walls of prokaryotic cells
- contains polysaccharides
State the differences between slime layers and capsules
- slime layers loosely attaches on the cell wall
- capsule attaches tightly on cell wall
Main functions of pili
- allow bacteria to adhere on surfaces
- DNA transfer between bacteria through pili in conjugation (mating process)
- protein projections on bacetria
How do virus infects bacetria
through baceriophage
- transfers DNA into bacetria through pili
Main function of flagella
- locomotion of the cells
What are flagella consists of and wehre are they present in
- microtubules
- present in some bacteria and some animal cells (sperm, swimming action)
What is the main function of cillia
- locomotion / moving substances inside organism
Suggest implications of the properties of cilla
- lumen of trachea: beating action can move mucus and unwanted materials from throat through swallowing and spitting
- oviduct: cell type that lines our oviducs have cilia that allows egg to move
Gram-positive bacteria
- thicker layer of peptidoglycan
- contains teichoic acid
- no outer membrane covering cell wall
Gram-negative bacteria
- thinner layer of peptidoglycan
- does not contain teichoic acid
- with outer membrane covering cell wall
Suggest a test to distinguish gram-positive and gram-negative bacteria
gram-staining (solvent + stain)
- stay purple: gram-postivie
- turn pink or red: gram-negative
Steps of gram-staining
- add crystal violet: primary stain to specimen (purple, purple)
- add iodine: as mordant to make dye less soluble = adhere to cell walls (purple, purple)
- add alcohol: wash away stain from gram-negative cell walls (purple, colourless)
- add safranin: counterstain = allows dye-adherance to gram-negative cell walls (purple, red)
Suggest three ways to catergorise bacteria
- by structure of cell wall
- by shape of bacteria
- by respiration requirement
What are three shapes of bacteria
- bacillus (rod)
- coccus (sphere)
- spirillus (spiral)
What are the three different types of respiration requirements of baceteria
- obligate aerobes
- obligate anaerobes
- facultative anaerobes
What are the differences between obligate aerobes, obligate anaerobes and facultative anaerobes
- obligate aerobes: aerobic respiration in presence of oxygen, can be killed in absence of oxygen
- obligate anaerobes: anaerobic respiration in absence of oxygen, can be killed in presence of oxygen
- facultative anaerobes: carry out aerobic respiration in presence of oxygen, anaerobic respiration in absence of oxygen, or both at the same time
How do you distinguish bacteria using test tube?
- obligate aerobes are concentrated near the mouth of test tube due to higher oxygen concentration
- facultative anaerobes are less concentrated in comparison
- obligate anaerobes are at the bottom of the test tube
State the endosymbiotic theory
- mitochondria and chloroplast in eukaryotic cells were once separate prokaryotic microbes
- prokaryote engulfed by phagocytosis
- evidence: presence of circular DNA and 70S ribosomes in mitochondria and chloroplasts
Organisation of cells
cells -> tissues -> organs -> systems
Define tissues
same type of a group of cells that serve the same function
Define organs
- different types of 2 or more groups of cells
- multi-functional
Define systems
- multiple organs connected to perform a large-scale function
Explain the significance of organisms made from many small microscopic cells
- total surface area to volume ratio of the organism is higher
- distance of each cell from the extracellular environment is shorter
- allow higher rate of exchange of materials of the cells with surrounding environment to accommodate the metabolic need for the metabolic activities of all its cells
what are four basic types of animal tissues
- connective
- epithelial
- muscle
- nervous
Definition of adaptains of a cell
special features to make the cell more suited for its function
Explain the adaptations of red blood cells
- no nucleus in mature red blood cells
- allow more space for packing more haemoglobins in the red blood cells
- higher rate of transport of oxygen by blood
Explain the adaptations of root hair cells
- long cytoplasmic extension
- larger surface area for absorption of water and minerals
- higher rate of absorption of water and minerals
State all structures that must be present in bacterial cells
- cell wall (peptidoglycan)
- cell membrane
- cytoplasm
- nucleoid
- 70S ribosomes
- food stores
Double membrane bound organelles in eukaryotes
- nucleus
- mitochondria
- chloroplasts
- amyloplasts
Single membrane bound organelles in eukaryotes
- Endoplasmic reticulum
- Golgi body
- Lysosomes
- Sap vacuoles
Non-membrane bound organelles in eukaryotes
- Ribosomes
- Centrosomes
- (Nucleolus)
Structures that may be present in bacterial cells
- slime layer and capsule
- flagellum
- pili
- pasmids
- mesosomes
Presence of cell wall in different types of cells
plant cells: yes (cellulose)
animal cells: no
prokaryotic cells: yes (peptidoglycan)
Presence of nucleus in different types of cells
plant cells: yes
animal cells: yes
prokaryotic cells: no (nucleoid region)
Presence of membrane-bound organelles in different types of cells
plant cells: yes
animal cells: yes
prokaryotic cells: no
Presence of chloroplasts in different types of cells
plant cells: yes
animal cells: no
prokaryotic cells: no
Presence of mitochondria in different types of cells
plant cells: yes
animal cells: yes
prokaryotic cells: no
Presence of vacuoles in different types of cells
plant cells: large central vacuole
animal cells: small vacuole
prokaryotic cells: small vacuoles (if present)
Presence of lysosomes in different types of cells
plant cells: rare or no
animal cells: yes
prokaryotic cells: no
Presence of centrioles in different types of cells
plant cells: no
animal cells: yes
prokaryotic cells: no
Presence of flagella / cilla in different types of cells
plant cells: rare (if present, simple)
animal cells: yes (complex)
prokaryotic cells: present (simple, flagellin)
Sizes of different types of cells
plant cells: 10-100μm
animal cells: 10-30μm
prokaryotic cells: 1-10μm
Shape of different types of cells
plant cells: rectangular or box-like
animal cells: irregular and flexible
prokaryotic cells: simple (sperical, rod-shaped)
Presence of endoplasmic reticulum in different types of cells
plant cells: yes
animal cells: yes
prokaryotic cells: no
Differences of genetic material in eukaryotes and prokaryotes
eukaryotes: linear DNA, histone, forms chromatin
prokaryotics: circular DNA, no histone, no chromatin
Differences in reproduction of eukaryotes and prokaryotes
eukaryotes: sexual or asexual
prokaryotes: asexual
Comparison of cellular natures of eukaryotes and prokaryotes
eukaryotes: unicellular / multicellular
prokaryotes: unicellular
State the differences between scanning electron microcsope and transmission electron microscope
scanning: 3D, maximum of 2million magnification, lower resolution
transmission: 2D, maximum of 50million magnification, higher resolution
