The Cellular Level of Organisation Flashcards
Cell theory
- Cells are the building blocks of all organisms
- All cells come from the division of preexisting cells
- Cells are the smallest units that carry out life’s essential physiological functions
- Each cell maintains homeostasis at the cellular level
Cytology
The study of cellular structure and function
Two types of human cells
Sex cells (sperm and oocytes) and somatic cells (all other cells)
Functions of the plasma membrane
- To seperate the cytoplasm from the extracellular fluid
- To control entry and exit of ions, nutrients, wastes, and secretions
- To sense changes in extracellular fluid through receptors
- To stabilise tissues
Phospholipid bilayer
Hydrophilic heads on the outside and hydrophobic tails on the inside
Function of cholesterol in the plasma membrane
To stiffen the plasma membrane, making it less fluid and less permeable
Two types of membrane proteins
Integral: part of the structure of the plasma membrane
Peripheral: bound to inner or outer surface of the membrane, easily separated from it
Anchoring proteins
Attach the plasma membrane to other structures and stabilise its position
Recognition proteins (identifiers)
Recognise other cells as normal or abnormal
Enzymes
Catalyse reactions in both cytosol and extracellular fluid (can be integral or peripheral)
Receptor proteins
Sense specific extracellular ions or molecules called ligands
Carrier proteins
Bind solutes and transport them across the plasma membrane
Intergral protein channel
Allow ion and small water-soluble substances to move across the plasma membrane
Why do ions need a protein channel to enter a cell?
They don’t dissolve in lipids and thus cannot cross the phospholipid bilayer
Rafts
Areas marking the location of anchoring proteins and some kinds of receptor proteins that are confined to specific areas of the plasma membrane
Why do most integral proteins drift across the surface of the membrane?
Because the membrane phospholipids are fluid at body temperature
Complex carbohydrates of the plasma membrane
Proteoglycans, glycoproteins, and glycolipids
Carbohydrate layer on plasma membrane
Glycocalx
Functions of the glycocalx
- To form a viscous layer that lubricates and protects the plasma membrane
- To anchor the cell in place with stickiness
- Glycoproteins and glycolipids can function as receptors
- Cells involved in the immune response recognise glycoproteins and glycolipids as normal or abnormal
Cytoplasm
The general term for the material between the plasma membrane and the membrane that surrounds the nucleus
Cytosol
The intracellular fluid made made from water and various dissolved and insoluble material
Which contains more proteins: cytosol or extracellular fluid?
Cytosol
Organelles
Internal structures of cells that perform most of the tasks that keep a cell alive and functioning normally
Two types of organelles
Non-membranous: not completely enclosed by membranes, and all of their components are in direct contact with the cytosol
Membranous: isolated from the cytosol by phospholipid membranes
Inclusions
Masses of insoluble materials e.g. glycogen granules and pigment granules
Cytoskeleton
Internal protein framework that gives the cell strength and flexibility
Protein that makes up microfilaments
Actin
Function of microfilaments
- To anchor cytoskeleton to integral proteins of the plasma membrane
- Determine the consistency of the cytosol (dense, flexible network = cytosol has gelatinous consistency, widely dispersed = cytosol is more fluid)
Additional microfilament in skeletal muscle cells
Thick myosin filaments, which interact with thin actin filaments to cause contraction
Terminal web
A layer of actin filaments present in cells that form a layer or lining, e.g. the lining of the intestinal tract
Components of the cytoskeleton
Microfilaments, intermediate filaments and microtubules
Function of intermediate filaments
- To strengthen the cell and help maintain its shape
- To stabilise the position of organelles
- To stabilise the position of the cell with respect to surrounding cells
Protein that makes up microtubules
The globular protein tubulin
What is the most durable cytoskeletal element?
Intermediate filaments
Function of microtubules
- To give the cell strength, maintain its shape, and anchor the position of major organelles
- To change the shape of the cell, and to assist in cell movement
- To move vesicles or other organelles within the cell through motor proteins
- To distribute duplicated chromosomes containing DNA to opposite ends of the dividing cell (to act as spindle apparatus)
- To form structural components of organelles, such as centrioles and cilia
Which element makes up the most of the cytoskeleton?
Microtubules
Which cytoskeletal element is made of molecules that assemble and disassemble?
Microtubules
Microvilli
Small, finger-shaped projections of the plasma membrane
Function of the microvilli
To increase the surface area of the cell
Which cells are covered with microvilli
Cells involved in actively absorbing material e.g. cells lining the digestive tract
Centrosome
Region of cytoplasm located next to nucleus in the cell, microtubule-organising centre of animal cells
Where do microtubules generally begin in the cell?
Centrosome
Centrioles
A pair of cylindrical structures that aid in the formation of the spindle apparatus needed in the movement of chromosomes in cell division
Arrangement of centrioles
9+0 array
Cilia
Fairly long, slender extensions of the plasma membrane
Two types of cilia
Nonmotile primary cilium: detects environmental stimuli
Multiple motile cilia: beat rhythmically to move fluids and secretions across the cell surface
Arrangement of nonmotile primary cilium
9+0 array
Arrangement of motile cilia
9+2 array
Arrangement of basal body
9+0 array
What is the basal body made of?
Centrioles
Strokes of motile cilia
Power stroke: relatively stiff
Return stroke: relatively flexible
Where are motile cilia found?
Cells lining the respiratory and reproductive tracts, and various other locations in the body
Ciliopathies
A wide range of human disorders caused by defective primary cilia
Flagellum
Long, whip-like extension of the plasma membrane
Arrangement of the flagellum
9+2 array
Which is the only type of human cell that has a flagellum?
Sperm cells
Ribosomes
The organelles responsible for protein synthesis
Composition of ribosomes
60% RNA and 40% protein
Two subunits of ribosomes
A small ribosomal subunit and a large ribosomal subunit which both contain special proteins and ribosomal RNA (rRNA)
What must happen before protein synthesis begins?
A small and large ribosomal subunit in the cytoplasm must join together with a strand of messenger RNA (mRNA)
Two major types of ribosomes
Free ribosomes: scattered throughout the cytoplasm (the proteins they make directly enter the cytosol)
Fixed ribosomes: temporarily fixed to the endoplasmic reticulum (the proteins they make enter the ER, modified and packaged for use, and then secreted)
Proteasomes
Organelles containing protein-digesting (proteolytic) enzymes, or proteases, that remove and recycle damaged or denatured proteins and play a role in the immune response
Recycling of damaged proteins
Cytoplasmic enzymes attach chains of ubiquitin (molecular “tags”) to proteins destined for recycling. Tagged proteins are quickly transported into a proteasome where they are rapidly disassembled into amino acids and small peptides, which are released into the cytoplasm.
Endoplasmic reticulum (ER)
A network of intracellular membranes continuous with the nucleus envelope, which surrounds the nucleus
Functions of the ER
- Synthesis of proteins, carbohydrates and lipids
- Storage of synthesised molecules or materials
- Transport within the ER
- Absorb toxins and neutralise them with enzymes