Anatomy of the Cell Flashcards
Composition of a Cell
water - 80%; protein - 15%; lipid 0 2.5%; carbohydrate - 1.5%; inorganic (sodium/phosphate etc.) - 1%
Eukaryotic Cell
a cell with a true nucleus
Common Features of Eukaryotic cells
outer membrane; inner cytosol; cytoskeleton; membrane bound organelles; inclusions.
Plasmalemma (Cell Membrane)
separates the cytoplasm from the outside environment. Is a layer of amphipathic phospholipid molecules with hydrophilic heads at the outer and inner surfaces and hydrophobic fatty acid chains facing towards the middle of the 2 layers. Contains integral proteins which the cell inserts into the membrane and gives the cell its ability to exocytose and endocytose material through the cell membrane.
Integral Proteins include
receptors; channels; transporters; enzymes; and cell attachment proteins.
Exocytose
move material (molecules) out of the cell.
Endocytose
substances are brought into the cell.
Properties of Plasmalemma
Is fluid, changes shape easily; is selectively permeable, highly permeable to water, oxygen, small hydrophobic molecules, virtually impermeable to charged ions (eg. Na+).
Organelles
Small, intracellular ‘organs’ with a specific function and structural organisation.
Mitochondria (organelle)
energy production
Rough Endoplasmic Reticulum (organelle)
protein synthesis
Smooth Endoplasmic Reticulum (organelle)
cholesterol and lipid synthesis/detoxification
Golgi Apparatus (organelle)
modification and packaging of secretions
Lysosomes (organelle)
hydrolytic enzymes for intracellular digestion
Nucleus (organelle)
contains genetic code
Inclusions
dispensable and may only be present for a short time. Represent components that have been synthesised by the cell itself (pigment, glycogen stores, lipid droplets, presecretion product) or taken up from the extracellular environment (endocytotic vesicle).
Cytoskeleton
function maintained by a set of filamentous cytosolic proteins, the cytoskeletal proteins. Three main types: Microfilaments composed of the protein actin; Intermediate filaments composed of six main proteins, which vary in different cell types; Microtubules composed of two tubulin proteins. These filamentous proteins attach to cell membrane and to each other by anchoring and joining proteins to form a dynamic 3D internal scaffolding.
Microfilaments
Composed of fine strands of the protein actin. Actin molecules can assemble into filaments and later dissociate making them very dynamic
Intermediate Filaments
bind intracellular elements together and to the plasmalemma. Different types divided into classes. Provide majority of structural integrity of cell.
Microtubules
hollow tubules composed of alpha and beta tubulin subunits in alternating array. Can be assembled and disassembled. Originate from centrosome and include stabilising proteins, microtubule-associated proteins (MAPS). Are polar. Important in cilia, flagella and mitotic spindle - cell movement.
Centrosome
microtubules radiate from this. Core of the centrosome contains a pair of centrioles which are composed of specialised microtubule segments.
Red Blood Cell
7 microns in diameter
Nucleus contains
chromosomes and is location of RNA synthesis. Both mRNA and tRNA are transcribed in the nucleus, and rRNA is transcribed in the nucleolus (a 1-3micrimetre diameter dense area within the nucleus).
Nucleus is enclosed by
a nuclear envelope, a double membrane with small fluid filled space (perinuclear membrane) between inner and outer membrane.
Euchromatin
DNA that is partially unwound, more dispersed, and actively undergoing transcription.
Heterochromatin
DNA is highly condensed (clumped) and not undergoing transcription.
Ribosomes
formed in the nucleus, required for protein synthesis. Each ribosome is made up of a small subunit - which binds RNA, and a large subunit - which catalyses the formation of peptide bonds.
Endoplasmic Reticulum
Forms a network of interconnecting membrane-bound compartments in the cell. Two types; rough and smooth.
Rough Endoplasmic Reticulum
Studded with ribosomes. Vital role in synthesis of proteins destined for insertion into membranes or for secretion. Cells relatively metabolically inactive have relatively little ER. Associated with protein synthesis and initiation of glycoprotein formation.
Smooth Endoplasmic Reticulum
continues processing of proteins produced in the RER. SER plays vital role as site of synthesis of lipids. Most cells contain relatively little SER
Golgi Apparatus (Complex)
composed of a group of flattened, membrane bound cisternae, arranged in sub compartments. Transport vesicles arrive from the SER/RER. Golgi cisterns function in the modification and packaging of macromolecules that were synthesised in ER (adds sugars, cleaves some proteins, sorts macromolecules into vesicles).
Mitochondria
Composed of an outer and inner membrane. Inner membrane is folded to form cristae, which increase available surface area. Function in the generation of ATP, via oxidative phosphorylation, and in the synthesis of certain lipids and proteins. Contain their own DNA and system for protein production.
Intracellular Junctions
specialised membrane structures which link cells together into a functional unit. Three types of junction: Occluding junction - link cells to form a diffusion barrier; Anchoring barrier - provide mechanical strength; Communicating junction - allow movement of molecules between cells.
Occluding Junctions (also known as tight junctions or zonula occludens)
Prevent diffusion. Appear as a focal region of close apposition between adjacent cell membranes
Anchoring Junction (also termed zonula adherens)
Two types: Adherent - attached to actin. Attaches skeleton of one cell to skeleton of another; Desmosome - very strong. Attached to intermediate filaments. Cells in epidermis are held together by thousands of desmosomes in every cell. Make skin strong.
Junctional Complex
Close association of several types of junctions found in certain epithelial tissues.
Communicating Junctions (often termed Gap Junctions)
Allow selective diffusion of molecules between adjacent cells. Each junction is a circular patch studded with several hundred pores, which were produced by connexon proteins. Found in epithelia, but also in some smooth muscle and in cardiac muscle, where it is critical for the spread of excitation.
Endocytosis
Material from extracellular space can be incorporated into the cell by endocytosis. The cell membrane invaginates, fuses and the newly made endocytotic vesicle buds into the cell.
Phagocytosis
Bacteria or larger particulate material from extracellular space can be incorporated into the cell by phagocytosis. Bacterium binds to the cell surface receptors, triggering extensions of the cell to engulf it forming a phagosome. This binds with a lysosome carrying digestive enzyme, producing a phagolysosome.
