Cell Ultrastructure Flashcards
(10 cards)
Components in a nucleus
Role of the nucleus, nuclear envelope, nucleoplasm, chromatin, nucleolus, centriole
Nucleus - direct protein synthesis
Nuclear envelope - 2 membranes separated by fluid-filled space, outer membrane continuous with RER, inner membrane associated with the nuclear lamina, perforated
Nucleoplasm - semi-fluid matrix, medium for the diffusion of metabolites
Chromatin - dispersed, entangled, & highly elongated threads. DNA in the nucleus, wrapped around histone proteins and packaged into chromosomes
Nucleolus - non-membrane bound structure of protein and nucleic acid, site of transcription of rRNA, assembly of ribosomal subunits
Centrioles/centrosomes - a pair of rod-like structures with 9 triplets of microtubules arranged in a ring, organise the synthesis & assembly of spindle fibres, determine the polarity of the cell
Components and function of a mitochondrion
Double membrane - inner membrane highly folded to form cristae,ETC & ATP synthase complexes present in abundance
Mitochondrial matrix - dense fluid, enzymes present for link rxn & krebs cycle, circular DNA & 70s ribosome present
circular/rod shaped
Involved in aerobic respiration to synthesise ATP molecules
Components and function of a chloroplast
Double membrane + thylakoid membranes
Granum (plural: grana) - 1 stack of thylakoid membrane connected by inter-granal lamellae, contains photosystem, ETC, ATP synthase complexes present in abundance on the thylakoid membrane
Chloroplast stroma - dense fluid, enzymes present for Calvin cycle, circular DNA & 70s ribosomes present
chloroplast - site of photosynthesis - light absorbing pigment embedded in thylakoid membrane involved in the conversion of light
Component and role of ribosome
EU - 80s, synthesised in the nucleolus
PRO - 70s, synthesised in the cytoplasm
ribosomes in clusters are known as polyribosomes
non-membranous organelle w small + large subunits containing rRNA complexed w proteins
The site of translation of mRNA to the polypeptide contains binding sites for tRNA & mRNA, enzyme peptidyl transferase activity present in the large subunit to catalyse formation of peptide bonds
Rough endoplasmic reticulum
Single membrane network of flattened membrane-bound sacs w ribosomes on its surface continuous w the nuclear envelope
Enzymes in ER lumen/cisternae space - post-translational modifications of protein synthesised by bound ribosomes
The temporary storage of secretory protein & site of protein synthesis
Smooth endoplasmic reticulum
Single membrane network of fine membranous tubules w/out ribosomes on its surface
Lipid synthesis - structural components, receptors for cell-cell adhesion, hormones, storage molecules
Detoxification of drugs & poison w enzymes
Storage of Ca+ required for muscle contraction
Golgi body
Single membrane network of flattened membrane-bound sacs/cisternae
Cis face - cisternae formed as transport vesicles fuse w the Golgi body
Trans face - cisternae are broken down to secretory vesicles/lysosomes, buds off from the Golgi body
Further post-translational modifications of proteins & lipids from ER
Sort & package protein (for secretory vesicles)
synthesis, chemical modification & transport of lipid
Aid in carbohydrate synthesis for the formation of cell walls in plants
3 functions of lysosome
A lysosome is formed when protein from Golgi body buds off the trans face, in a primary vesicle/lysosome
1. Compartmentalize hydrolytic enzymes from the rest of the cell
Provides a space where cells can digest macromolecules safely, w/out the general destruction that would occur if hydrolytic enzymes are not kept apart from the cell
2. Autophagy - digest worn-out organelles w/in the cell
A double membrane surrounds the worn-out organelle to form autophagosome, products formed are absorbed & assimilated into the cytoplasm of the cell
3. Autolysis- self-digestion of the cell
Products of digestion are absorbed & assimilated into the cytoplasm of surrounding cells, which only occurs after cell death/cell damage
[Autophagosome = double membrane vesicle that encloses cellular constituents to be digested during autophagy
Phagosome = vesicle formed by wrapping membrane around foreign matter - phagocytosis
Endosome = formed by endocytosis & involves invagination of cells’ plasma membrane]
Glycogen & Starch - amylose & amylopectin
α-glucose molecules linked by α(1,4)glycosidic bonds which are then coiled into a helix w 6 residues per turn
Helical shape held by hydrogen bonds between -OH groups in the same amylose chain
-OH groups are projected into the interior of the helix, preventing the formation of cross-links between diff amylose chains, leading to low solubility
amylose - unbranched
amylopectin - branch points formed by α(1,6)glycosidic bonds
Glycogen - similar to amylopectin but is more extensively branched & more compact than amylopectin
SPF of carbohydrates
- Large molecules & most hydrophilic -OH groups projected into the interior of helices, thus insoluble in water & can be stored in large quantities w/out greatly affecting the water potential of the cell
- Helical structure, most hydrophilic -OH group projects into the interior of helices, chains cannot cross-link to form bundles. Thus, the individual chains can fold into very compact shapes & can be stored in large quantities w/in a limited space in the cells
- Presence of various branch points & chains do not cross-link makes chains easily broken down by hydrolytic enzymes into glucose, allowing glucose to be readily supplied for use
