The Cellular Level of Organisation Flashcards
(164 cards)
1
Q
Cell theory
A
- 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
2
Q
Cytology
A
The study of cellular structure and function
3
Q
Two types of human cells
A
Sex cells (sperm and oocytes) and somatic cells (all other cells)
4
Q
Functions of the plasma membrane
A
- 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
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Q
Phospholipid bilayer
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Hydrophilic heads on the outside and hydrophobic tails on the inside
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Q
Function of cholesterol in the plasma membrane
A
To stiffen the plasma membrane, making it less fluid and less permeable
7
Q
Two types of membrane proteins
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Integral: part of the structure of the plasma membrane
Peripheral: bound to inner or outer surface of the membrane, easily separated from it
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Q
Anchoring proteins
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Attach the plasma membrane to other structures and stabilise its position
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Q
Recognition proteins (identifiers)
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Recognise other cells as normal or abnormal
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Q
Enzymes
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Catalyse reactions in both cytosol and extracellular fluid (can be integral or peripheral)
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Q
Receptor proteins
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Sense specific extracellular ions or molecules called ligands
12
Q
Carrier proteins
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Bind solutes and transport them across the plasma membrane
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Q
Intergral protein channel
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Allow ion and small water-soluble substances to move across the plasma membrane
14
Q
Why do ions need a protein channel to enter a cell?
A
They don’t dissolve in lipids and thus cannot cross the phospholipid bilayer
15
Q
Rafts
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Areas marking the location of anchoring proteins and some kinds of receptor proteins that are confined to specific areas of the plasma membrane
16
Q
Why do most integral proteins drift across the surface of the membrane?
A
Because the membrane phospholipids are fluid at body temperature
17
Q
Complex carbohydrates of the plasma membrane
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Proteoglycans, glycoproteins, and glycolipids
18
Q
Carbohydrate layer on plasma membrane
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Glycocalx
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Q
Functions of the glycocalx
A
- 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
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Q
Cytoplasm
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The general term for the material between the plasma membrane and the membrane that surrounds the nucleus
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Cytosol
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The intracellular fluid made made from water and various dissolved and insoluble material
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Q
Which contains more proteins: cytosol or extracellular fluid?
A
Cytosol
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Q
Organelles
A
Internal structures of cells that perform most of the tasks that keep a cell alive and functioning normally
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Q
Two types of organelles
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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
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Inclusions
Masses of insoluble materials e.g. glycogen granules and pigment granules
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Cytoskeleton
Internal protein framework that gives the cell strength and flexibility
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Protein that makes up microfilaments
Actin
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Function of microfilaments
1. To anchor cytoskeleton to integral proteins of the plasma membrane
2. Determine the consistency of the cytosol (dense, flexible network = cytosol has gelatinous consistency, widely dispersed = cytosol is more fluid)
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Additional microfilament in skeletal muscle cells
Thick myosin filaments, which interact with thin actin filaments to cause contraction
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Terminal web
A layer of actin filaments present in cells that form a layer or lining, e.g. the lining of the intestinal tract
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Components of the cytoskeleton
Microfilaments, intermediate filaments and microtubules
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Function of intermediate filaments
1. To strengthen the cell and help maintain its shape
2. To stabilise the position of organelles
3. To stabilise the position of the cell with respect to surrounding cells
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Protein that makes up microtubules
The globular protein tubulin
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What is the most durable cytoskeletal element?
Intermediate filaments
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Function of microtubules
1. To give the cell strength, maintain its shape, and anchor the position of major organelles
2. To change the shape of the cell, and to assist in cell movement
3. To move vesicles or other organelles within the cell through motor proteins
4. To distribute duplicated chromosomes containing DNA to opposite ends of the dividing cell (to act as spindle apparatus)
5. To form structural components of organelles, such as centrioles and cilia
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Which element makes up the most of the cytoskeleton?
Microtubules
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Which cytoskeletal element is made of molecules that assemble and disassemble?
Microtubules
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Microvilli
Small, finger-shaped projections of the plasma membrane
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Function of the microvilli
To increase the surface area of the cell
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Which cells are covered with microvilli
Cells involved in actively absorbing material e.g. cells lining the digestive tract
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Centrosome
Region of cytoplasm located next to nucleus in the cell, microtubule-organising centre of animal cells
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Where do microtubules generally begin in the cell?
Centrosome
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Centrioles
A pair of cylindrical structures that aid in the formation of the spindle apparatus needed in the movement of chromosomes in cell division
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Arrangement of centrioles
9+0 array
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Cilia
Fairly long, slender extensions of the plasma membrane
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Two types of cilia
Nonmotile primary cilium: detects environmental stimuli
| Multiple motile cilia: beat rhythmically to move fluids and secretions across the cell surface
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Arrangement of nonmotile primary cilium
9+0 array
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Arrangement of motile cilia
9+2 array
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Arrangement of basal body
9+0 array
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What is the basal body made of?
Centrioles
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Strokes of motile cilia
Power stroke: relatively stiff
| Return stroke: relatively flexible
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Where are motile cilia found?
Cells lining the respiratory and reproductive tracts, and various other locations in the body
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Ciliopathies
A wide range of human disorders caused by defective primary cilia
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Flagellum
Long, whip-like extension of the plasma membrane
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Arrangement of the flagellum
9+2 array
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Which is the only type of human cell that has a flagellum?
Sperm cells
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Ribosomes
The organelles responsible for protein synthesis
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Composition of ribosomes
60% RNA and 40% protein
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Two subunits of ribosomes
A small ribosomal subunit and a large ribosomal subunit which both contain special proteins and ribosomal RNA (rRNA)
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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)
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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)
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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
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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.
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Endoplasmic reticulum (ER)
A network of intracellular membranes continuous with the nucleus envelope, which surrounds the nucleus
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Functions of the ER
1. Synthesis of proteins, carbohydrates and lipids
2. Storage of synthesised molecules or materials
3. Transport within the ER
4. Absorb toxins and neutralise them with enzymes
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Cisternae
Chambers within the ER that store water
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Two types of ER
```
Smooth ER (SER): no fixed ribosomes
Rough ER (RER): fixed ribosomes
```
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Functions of the SER
1. Synthesis of phospholipids and cholesterol for plasma membrane, ER, nuclear membrane and Golgi apparatus
2. Synthesis of steroid hormones
3. Synthesis and storage of glycerides in liver and fat cells
4. Synthesis and storage of glycogen in skeletal muscle and liver cells
5. Absorption of calcium ions in muscle cells, neurons and other types of cells
6. Detoxification of drugs in liver and kidney cells
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Functions of the RER
To synthesis proteins through the fixed ribosomes and then chemically modify and packaged for export to the Golgi apparatus
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Transport vesicles
Small, membranous sacs that pinch off from the tips of the cisternae of the RER and then deliver their contents to the Golgi apparatus
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Functions of the Golgi apparatus
1. Modifies and packages secretions for release from the cell
2. Adds or removes carbohydrates to or from proteins to chain their structure and function
3. Renews or modifies the plasma membrane
4. Packages special enzymes within lysosomes for use in the cytoplasm
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Protein synthesis
1. A gene on DNA produces mRNA, the template for protein synthesis
2. mRNA leaves the nucleus and attaches to a free ribosome in the cytoplasm or a fixed ribosome on the RER
3a. Proteins constructed on free ribosomes are released into the cytosol for use within the cell
3b. Protein synthesis on fixed ribosomes occurs at the RER. The newly synthesised protein folds into its 3D shape.
4. The proteins are modified within the ER. Regions of the ER then bud off, forming transport vesicles containing modified proteins and glycoproteins
5. The transport vesicles carry the proteins and glycoproteins towards the Golgi apparatus. The transport vesicles then fuse to create the forming (cis) face of the Golgi apparatus.
6. Multiple transport vesicles combine to form cisternae on the cis face. Further packaging and modification occur as the cisternae move towards the maturing (trans) face.
7. The trans face generates vesicles that carry modified proteins away from the Golgi apparatus.
8.
Lysosomes: released into the cell
Secretory vesicles: fuse with the plasma membrane and empty their products outside the cell by exocytosis
Membrane renewal vesicles: add new lipids and proteins to the plasma membrane
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Lysosomes
Vesicles that provide an isolated environment for potentially dangerous chemical reactions and contain digestive enzymes that break organic polymers into monomers
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Lysosomes functions
1. To fuse with the membrane of a damaged organelle
2. To fuse with an endosome containing fluid or solid materials from outside the cell
3. The lysosomal membrane breaks down during autolysis following cellular injury or death
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Which is smaller: lysosomes or peroxisomes?
Peroxisomes
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How are peroxisomes produced?
Through the division of exisiting peroxisomes
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Function of peroxisomes
To break down organic molecules and protect the cell from free radicals
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Mitochondria
The organelles that produce ATP for the cell
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Structure of mitocondria
Double membrane - outer membrane surrounds the organelle, inner membrane folds to create cristae which surrounds the matrix of the mitochondrion
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Why is the inner membrane of the mitochondria folded?
To increase SA
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Aerobic metabolism
1. Glycolysis - glucose molecules are broken down into 2 molecules of pyruvate which are then absorbed the the mitochondrion
2. A CO2 molecule is removed from each pyruvate molecule
3. Remnants of the pyruvate molecules undergo the citric acid cycle (CO2 released from cell, electron transferred from H to O
4. Energy released allows enzymatic conversion of ADP to ATP
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Which membranous organelle isn't in communication with the others through vesicles?
Mitochondria
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Membrane flow
The continuous movement and exchange of membrane segments
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Structure of the nucleus
Nuclear envelope - double membrane separated by a narrow perinuclear space
Nuclear pores - openings in the nuclear envelope that receive chemical communication
Nucleoplasm - contains nuclear matrix (network of fine filaments)
Nucleoli - synthesise rRNA, ribosomal subunites (made of RNA, enzymes and proteins called histones)
Nucleosome - DNA winded around histones
Chromatin - tangle of fine filaments (non-dividing cells)
Chromosomes - tight structures just before division begins
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Why doesn't DNA flow out of nuclear pores?
DNA molecules are too big
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Composition of amino acids
Three nitrogenous bases = 1 amino acid
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Gene
Functional unit of heredity, the sequence of nucleotides of a DNA strand that specifies the amino acids needed to produce a certain protein
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Gene activation
A process in which the portion of the DNA molecule containing a gene uncoils and the histones are temporarily removed
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Transcription
The synthesis of RNA from a DNA template
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mRNA
Carries the information needed to synthesis proteins
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Coding strand of DNA
The strand containing the triplets that specify the sequence of amino acids in the polypeptide
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Template strand of DNA
The strand containing the complementary triplets that will be used as a template for mRNA production
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mRNA transcription
1. Once DNA strands have separated and histone have been removed, the enzyme RNA polymerase binds to the promoter of a gene on the template strand
2. At the "start signal, RNA polymerase strings template strand nucleotides and complementary nucleotides in the nucleoplasm together through covalent bonding creating mRNA strand. T is never used in mRNA strand
3. At the "stop" signal, the enzyme and mRNA strand detach from the DNA strand
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Codon
Three-base mRNA sequence with nitrogenous bases complementary to those of the triplets in the DNA strand
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RNA processing
A process in which noncoding intervening sequences (introns) are snipped out and the remaining coding segments (exons) are spliced together
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Translation
The formation of a linear chain of amino acids (polypeptide) using the information from an mRNA strand
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Initiation (process of translation)
1. Amino acids provided by tRNA (tail of tRNA binds to amino acid)
2. tRNA anticodon bonds with a complementary mRNA codon
3. Small and large ribosomal subunits join together and enclose mRNA and tRNA (large ribosomal subunit has three sites for RNA binding: E, exit; P, polypeptide binding; A, arrival)
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Anticodon
Loop made by tRNA containing three nitrogenous bases
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Elongation (process of translation)
1. Ribosome moves one codon father. Another tRNA arrives at A, carrying amino acid 2, initiation repeats, ribosomal enzyme attaches amino acid 1 to amino acid 2
2. A third tRNA arrives at the A, tRNA at E leaves
3. Elongation continues until it reaches a stop codon
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Termination (process of translation)
A protein release factor bonds with the stop codon, releasing the polypeptide
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Signalling pathway
Form intracellular signalling molecules
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Types of membrane permeability
Impermeable, freely permeable and selectively permeable
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Diffusion
The net movement of a substance from an area of higher concentration to an area of lower concentration
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Concentration gradient
Difference between the high and low concentrations of a substance
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Factors influencing diffusion rates
1. Distance (shorter = faster)
2. Ion and molecule size (smaller = faster)
3. Temperature (hotter = faster)
4. Concentration gradient (steeper = faster)
5. Electrical gradient
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Simple diffusion
Alcohols, fatty acids, steroids, water, dissolved gases (oxygen and CO2), and lipid-soluble drugs can diffuse through the plasma membrane the membrane
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Channel-mediated diffusion
Ions and water-soluble compounds must enter the cell through channel-mediated diffusion
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Leak channels
Membrane channels that are always open
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Osmosis
Water molecules tend to flow across a selectively permeable membrane toward the solution with the higher solute concentration, because that is where the concentration of water is lower
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Osmotic pressure
An indication of the force with which pure water moves into a solution as a result of its solute concentration
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Aquaporins
Abundant water channels
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Hydrostatic pressure
Pressure generated from pushing against a fluid
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Osmolarity
The total solute concentration in an aqueous solution
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Tonicity
The effects of various osmotic solutions on cells
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Isotonic
Equal solute concentration
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Hypotonic
The solution with the lower solute concentration
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Hypertonic
The solution with the higher solute concentration
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Hemolysis
When a RBC is put into a hypotonic solution, it swells up and bursts
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Crenation
When a RBC is put into a hypertonic solution, it shrinks
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Carrier-mediated transport
The process in which integral proteins bind specific ions or organic substrates and carry them across the plasma membrane
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Characteristics of carrier-mediated transport
1. Specificity
2. Saturation limits
3. Regulation
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Symport mechanism
The carrier protein (symporter) transports 2 different molecules or ions through a membrane in the same direction
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Antiport mechanism
The carrier protein (antiporter) transports 2 different molecules or ions in opposite directions
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Facilitated diffusion
The process in which substances are passively transported across the membrane by carrier proteins. The molecule binds to the receptor site on the carrier protein, the protein changes shape, moving the molecule across the membrane and into the cytoplasm e.g. glucose
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Active transport
Process in which a high-energy bond provides the energy needed to move ions or molecules across the membrane
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Ion pumps
Carrier proteins that actively transport the cations: sodium, potassium, calcium and magnesium
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Primary active transport
The process of pumping solutes against a concentration gradient using energy from ATP
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Sodium-potassium pump
The sodium ion concentration is high in the extracellular fluid, but low in the cytoplasm (and vice versa for potassium). Leak channels allow sodium ions to diffuse into the cell and potassium ions to diffuse out. Homeostasis requires that sodium ions be ejected and potassium ions be reclaimed
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How many sodium and potassium ions are moved per 1 ATP molecule?
3 sodium ejected and 2 potassium reclaimed
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Secondary active transport
The transport mechanism itself does not require energy from ATP, but the cell often needs to expend ATP at a later time to preserve homeostasis
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Endocytosis
The process in which extracellular materials can be packaged into vesicles at the cell surface and imported into the cell
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Three major types of endocytosis
1. Receptor-mediated endocytosis
2. Pinocytosis
3. Phagocytosis
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Receptor-mediated endocytosis
The process in which cholesterol and iron irons enter the cell through clathrin-coated pits
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Pinocytosis
The formation of endosomes filled with extracellular fluid (a pocket forms in the plasma membrane that then pinches off)
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Phagocytosis
The formation of endosomes (called phagosomes) containing solid objects (cytoplasmic extensions called pseudopodia surround the object and their membranes fuse to form a phagosome which then fuses with lysosome whose enzymes digest its contents
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Exocytosis
The process in which a vesicle forms inside the cell and fuses with the plasma membrane
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Transcytosis
The process in which endocytosis produces vesicles on one side of the cell that are discharged through exocytosis on the other side of the cell
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Charges of the surfaces of the plasma membrane
The cytoplasm-facing surface has a slight negative charge with respect to the extracellular surface (only in relation to surfaces - not relevant to contents)
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Causes for the charges on the surfaces of the plasma membrane
Cytoplasm-facing surface: negative due to negatively charged protein anions that are too large to pass through any membrane ion channels
Extracellular surface: positive due to sodium cations
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Potential difference
When positive and negative charges are held apart
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Membrane potential
The potential difference across the plasma membrane
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Resting membrane potential
The membrane potential in an unstimulated or undisturbed cell
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Apoptosis
The genetically controlled death of cells
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Interphase
The stage of the cell life cycle between mitotic division
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G0 phase
An interphase cell in a non-dividing state
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DNA replication
1. Helicases unwind the DNA strands while DNA polymerase bind to exposed nitrogenous bases
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Mitosis
The duplication of the chromosomes in the nucleus and their separation into 2 identical set
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Cytokinesis
The division of the cytoplasm during mitosis, beginning in late anaphase and continuing through telephase
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Miotic rate
Rate of cell division
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Phases of mitosis
Prophase, metaphase, anaphase and telophase
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Growth factors
Various natural body substances derived from food can stimulate the division of specific types of cells
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Telomeres
Terminal segments of DNA associated proteins
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Functions of telomeres
To attach chromosomes to the nuclear matrix and protect the end of the chromosomes from damage during mitosis
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Repressor genes
Genes that inhibit cell division
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Tumor
A mass produced by abnormal cell growth and division
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Benign tumour
The cells usually remain in the tissue where the tumour originated
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Malignant tumour
The cells aren't confined to originating tissue
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Primary tumour
Tumour of origin
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Invasion
The tumour spreading process
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Cause of cancer
The abnormal proliferation of any of the cells in the body
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Oncogenes
Mutated genes
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Mutagens
Agents that can cause a mutation
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Carcigonens
Cancer-causing agents
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Cellular differentiation
The development of specific cellular characteristics and functions that are different from the original cell
