Topic 1.2 Flashcards
Cytoplasm
internal fluid component of the cell
Nucleoid
region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
Plasmids
autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)
Ribosomes
complexes of RNA and protein that are responsible for polypeptide synthesis (prokaryote ribosome = 70S)
Cell membrane
Semi-permeable and selective barrier surrounding the cell
Cell wall
rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis)
Slime capsule
a thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis
Flagella
Long, slender projections containing a motor protein that enables movement (singular: flagellum)
Pili
Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)
Protista
unicellular organisms; or multicellular organisms without specialised tissue
Fungi
have a cell wall made of chitin and obtain nutrition via heterotrophic absorption
Plantae
have a cell wall made of cellulose and obtain nutrition autotrophically (via photosynthesis)
Animalia
no cell wall and obtain nutrition via heterotrophic ingestion
Ribosomes
Structure: Two subunits made of RNA and protein; larger in eukaryotes (80S) than prokaryotes (70S)
Function: Site of polypeptide synthesis (this process is called translation)
Cytoskeleton
Structure: A filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol)
Function: Provides internal structure and mediates intracellular transport (less developed in prokaryotes)
Plasma membrane
Structure: Phospholipid bilayer embedded with proteins (not an organelle per se, but a vital structure)
Function: Semi-permeable and selective barrier surrounding the cell
Nucleus
Structure: Double membrane structure with pores; contains an inner region called a nucleolus
Function: Stores genetic material (DNA) as chromatin; nucleolus is site of ribosome assembly
Endoplasmic Reticulum
Structure: A membrane network that may be bare (smooth ER) or studded with ribosomes (rough ER)
Function: Transports materials between organelles (smooth ER = lipids ; rough ER = proteins)
Golgi Apparatus
Structure: An assembly of vesicles and folded membranes located near the cell membrane
Function: Involved in the sorting, storing, modification and export of secretory products
Mitochondrion
Structure: Double membrane structure, inner membrane highly folded into internal cristae
Function: Site of aerobic respiration (ATP production)
Peroxisome
Structure: Membranous sac containing a variety of catabolic enzymes
Function: Catalyses breakdown of toxic substances (e.g. H2O2) and other metabolites
Centrosome
Structure: Microtubule organising centre (contains paired centrioles in animal cells but not plant cells)
Function: Radiating microtubules form spindle fibres and contribute to cell division (mitosis / meiosis)
Chloroplast
Structure: Double membrane structure with internal stacks of membranous discs (thylakoids)
Function: Site of photosynthesis – manufactured organic molecules are stored in various plastids
Vacuole (large and central)
Structure: Fluid-filled internal cavity surrounded by a membrane (tonoplast)
Function: Maintains hydrostatic pressure (animal cells may have small, temporary vacuoles)
Cell Wall
Structure: External outer covering made of cellulose (not an organelle per se, but a vital structure)
Function: Provides support and mechanical strength; prevents excess water uptake
Lysosome
Structure: Membranous sacs filled with hydrolytic enzymes
Function: Breakdown / hydrolysis of macromolecules (presence in plant cells is subject to debate)
TEM
2D- through the object
SEM
3D
Structure of Phospholipids:
- Consist of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
- Consist of two non-polar tails (hydrophobic) composed of fatty acid (hydrocarbon) chains
- Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic
Arrangement in Membranes:
- Phospholipids spontaneously arrange into a bilayer
- The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids, while the two hydrophilic head regions associate with the cytosolic and extracellular fluids respectively
Properties of the Phospholipid Bilayer:
- The bilayer is held together by weak hydrophobic interactions between the tails
- Hydrophilic / hydrophobic layers restrict the passage of many substances
- Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility
- This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)
Integral proteins
permanently attached to the membrane and are typically transmembrane (they span across the bilayer)
Peripheral proteins
temporarily attached by non-covalent interactions and associate with one surface of the membrane
