Cells Flashcards
What is modern cell theory?
- A cell is the smallest basic unit of life
- All living organisms are made of 1/more cells
- Cells arise from pre-existing cells by CELL DIVISION
- Cells contain genetic material passed from parent to daughter cell
- All metabolic processes occur within cells
What do all cells have?
- Cell surface membrane
- Cytosol (semi fluid substance)
- Genetic material (DNA,RNA) [carries genes]
- Ribosomes (manufacture protein)
Differences betw. Eukaryotic & Prokaryotic cells
Eukaryotes [multicellular organisms]
- Contain a membrane enclosed nucleus & membrane bound organelles
Prokaryotes [unicellular, mitochondria, chloroplasts]
- LACK a membrane enclosed nucleus & membrane bound organelles
Structure + purpose of cell surface membrane
[Phospholipid bilayer]
Consists of phospholipids arranged in a bilayer, with hydrophobic fatty acid tails facing inwards and hydrophilic phosphate heads facing the aqueous environment
Functions as selective barrier that allows passage if enough O², nutrients, waste to meet metabolic needs of the cell
Explain the structure of cell surface membrane
Exp:
- Exists as a stable boundary betw 2 aqueous compartments due to molecular arrangement. (Shelter hydrophobic tails from water, expose hydrophilic heads to water)
- Phospholipids are AMPHIPATHIC
[both hydrophobic & hydrophilic regions]
Amphipathic allows for reseal of bilayer membrane when disrupted
- Bilayer is dynamic, “fluid mosiac model”
What are the 6 parts of the nucleus?
Nuclear envelope
Nuclear matrix
Nuclear lamina
Nucleolus
Nucleoplasm
Genetic material/chromatin
Structure and function of nuclear envelope
[STRUCTURE]
- Double membraned, encloses nucleus
- Outer membrane is continuous with RER
- Intermembrane space exists betw Outer & inner membrane
- Membrane perforated by nuclear pores, each formed by a protein pore complex
[FUNCTION]
(Protein pore complex)
- Regulates exit of RNAs
- Entry of proteins, ATP & nucleotides
Structure and function of nucleoplasm
- Semi fluid substance that fills nucleus
- Contains chromatin, nucleolus, proteins(enzymes), nucleotides and ions
Structure and function of nucleolus
[STRUCTURE]
Large, densely stained area
1 or more in nucleoplasm
*Contains large loops of DNA w rRNA genes -> transcribed to produce rRNA
[FUNCTION]
1. Site of transcription of rRNA genes to produce rRNA
2. Assembly of ribosomal proteins + rRNA to form large & small units if ribosomes
(contains DNA, rRNA, ribosomal proteins)
Structure & function of chromatin
- Molecule of DNA coiled around proteins known as histones
EUCHROMATIN (lightly stained)
- loosely coiled, transcriptionally active genes
HETEROCHROMATIN (densely stained)
- tightly coiled, transcriptionally inactive genes
During nuclear division
-> chromatin threads condense to form chromosomes
Ribosome structure
70s -> Prokaryotes (chloroplast & mitochondrion)
80s -> Eukaryotes
Ribosome -> complex of rRNA & proteins [No membrane]
- Made up of 1 large & small subunit
- Subunit made up of rRNA + ribosomal formed in nucleolus
- large & small subunits assembled in cytosol to form functional ribosome
Ribosome types and their function
FREE & BOUND differences
Free [WITHIN CELL]
- proteins released in cytosol, used within cell [eg. cytosolic proteins, glycolytic enzymes]
Bound
1. membrane- anchored proteins (hormone receptors, binding site initially faces inwards)
2. protein destined for secretion (insulin)
3. Packing of hydrolytic enzymes in lysosomes
Many ribosomes are attached to single mRNA molecule during translation -> poly(ribo)somes
Polysomes increases rate
- translated simultaneously, producing many copies at same time
Structure & function of RER
[STRUCTURE]
Made of flattened sacs, interconnected and continuous w nuclear envelope
- studded w ribosomes for protein synthesis
[FUNCTION]
1) polyp. chains synthesised by ribosome (free/bound) enter RER lumen,
2) fold into 3D conformation, tertiary/quaternary structure & undergo biochemical modification eg. glycosylation
3) Transport vesicles carrying protein bud off from ER
Structure & function of SER
(5 func)
- Tubular cisternae, interconnected w each other
5 functions: (LEDmetaCa2+)
1. Synthesis & transport of lipids (oils, steroids, phospholipids)
2. SER contains ENZYMES that make phospholipids, helps to replenish phospholipid bilayer of CSM
3. Detox of drugs & poisons (liver)
4. Metabolise carbohydrates (liver)
5. Storage of Ca2+ (muscles)
Structure of GA
Stack of FLATTENED & CURVED single membrane-bound sacs (cisternae)
Cis face (receive)
Constantly formed from fusion of vesicles from RER & SER
Trans face (shipping)
Products move from cis to trans through REPEATED BUDDING & FUSION of vesicles; undergo biochemical mods,
BUD off as
1. Primary lysosome
2. Golgi vesicles
3. Secretory vesicle
Function of GA (7)
Receives proteins & lipids at cis face, further biochemical mod. via repeated budding & fusion of vesicles
- Modifies large amt of hydrolytic enzymes in primary lysosome (phagocyte)
- Glycosylation (glycolipids & glycoprotein)
- carbohydrates modified in GA - Hydroxylation (fibroblast cell)
- Add OH to collagen polypeptides - Replenishment of CSM lost via endocytosis
- Formation of primary lysosome
- Synthesis of certain macromolecules(pectin)
- Formation of cell plate in plant cells during cytokinesis
3 Structure of lysosome
- Spherical sacs 0.2-0.5 um
- Contains hydrolytic enzymes (acid hydrolases) optimal pH 5
- Storage vesicle, keep enzyme apart from rest of cell
- Maintained by proton pump on lysosomal membrane, **actively transport protons from cytosol into lysosome
What r the 3 functions of lysosome
1 Intracellular digestion
- Enables cell digest materials via endocytosis
Phagocytosis (solid) via pseudopodia
Pinocytosis (fluid)
Receptor-mediated endocytosis
2 Autophagy
- Destruction of wornout organelles
- Primary lysosome fuse with vesicles to form secondary lysosome, digested products discharged by exocytosis
3 Autolysis
- Self destruction of cell, release of contents
Describe structure of mitochondria
(Found in all eukaryotes)
- Doubled membrane, inner is selectively permeable, extensively folded into cristae
- increased SA for enzyme attachment for cellular respiration
- Contains intermembrane space, high conc. of H+ , establishes proton gradient
Contains mitochondrial matrix
- Mixture of proteins & lipids
- Circular DNA
- 70s ribosomes
- stalked particles on inner membrane (ATP synthase)
Describe function of mitochondrion
Site of synthesis of ATP for all cellular function
Lipid metabolism,
Lipid synthesis
Apoptosis - release of certain mitochondrial proteins in cytosol (cell death)
Mitochondrion moves by cytoplasmic streaming, where ATP required
Chloroplast structure & function
(3 structural components)
Site of p/s
3 membranes
Double membrane w intermembrane space + thylakoid membrane
1) Chloroplast envelope (outer & inner mem.)
- Compartmentalisation & specialisation of chloroplast for p/s
2) Thylakoid membrane (Light dpt)
Thylakoids: Stacks of flattenned interconnected sacs
Stacks of it -> Granum pl. Grana
Intergranal lamellae, phospholipid layer impermeable to protons -> proton gradient
3) Stroma (Fluid surrounding thylakoid, Light Indpt)
- Circular DNA -> genes e- carriers & enzymes in light indpt
- 70s ribosomes
- enzymes involved in p/s
- starch granules
- Gel- like medium
Centriole structure & function
(Not in plants, only eukaryotes)
- In pairs, 90° each other (found in centrosome, near nucleus)
- 9 triplets of microtubules, give a rod-like structure, not bound by membrane
FUNCTION:
Organisation of spindle fibres during nuclear division
- Single centriole found at cilia/flagellum
Structure & function of plant cellulose cell wall
made up of
1. Cellulose microfibrils
2. Pectin
3. Hemicelluloses
Pectin & hemicelluloses synthesised in GA, transported via golgi vesicles
Cellulose microfibrils synthesised directly on CSM
FUNCTION:
- provide tensile strength
- Maintain cell shape & structure
- protect plant cells against mechanical & osmotic stress
Organelles & no. of membranes
0 Phospholipid bilayer (membrane)
- ribosomes
- centrioles
1 membrane
- CSM
- ER
- GA
- Lysosome
- Vesicle
2 membrane
- Nucleus
- Mitochondria
- Chloroplast
***R/S of protein synthesis (or lipid)
- DNA in nucleus serves as template to synthesise mRNA, transported out of nuclear pore into cytosol
- mRNA either free (within cell) or bound (secreted or membrane-anchored)
mRNA-ribosome complex formed in cytosol - polyp. chain enters ER lumen, folds into 3D conformation, may undergo biochemical mods (glycosylation)
- ER vesicles bud off travel to cis face GA
- ER vesicles fuse w GA
- Further biochem mod. as protein travels thru. GA via repeated budding & fusion of vesicle
- At trans face, modded protein sorted & packaged into Golgi vesicle, bud off GA
LASTLY to 1/3 destinations
1. Secretory vesicle w secretory protein, fuses CSM secrete out contents via exocytosis (secretory pathway)
- Golgi vesicle w. embedded transmembrane protein RECEPTOR BINDING SITE FACING INWARDS fuses w CSM and gets embedded
- Primary lysosome, carries hydrolytic enzymes
Structures in all bacterium
Cell membrane
Cytoplasm
1 circular bacterial chromosome (nucleoid region)
70s ribosomes
Peptidoglycan cell wall
Structures in some bacterium
≥1 plasmid (extrachromosomal DNA)
Pilus & fimbria
Capsule/slime layer
Flagellum
Components of viruses?
/How is it identified by its structural components?
- nucleic acid/genome
- capsid
- MAY have viral envelope (phospholipid bilayer, enveloped in glycoproteins)
- NO cellular organisation (cytoplasm, ribosome)
CAPSID
- enclose & protect viral genome
- contain protein
- viral enzymes for replication
Why do viruses challenge cell theory?
Obligate intracellular parasites
Both living & non living
LIVING
- Possess genetic material
- can reproduce within host cell
- adapt to environmental conditions
NON-LIVING
- do not have cellular organisation
- cannot carry out metabolic processes on their own
- cannot reproduce independently via cell division from existing cells
