Chapter 3 - Cells Flashcards
3 major parts of a cell
- Nucleus
- Cytoplasm
Cell membrane
- Cytoplasm
Signal Transduction
series of biochemical reactions which allow cells to receive and respond to messages reaching the cell membrane
Membrane Proteins structure
- can either be globular, fibrous or rodlike in shape
- Integral meaning extending into the bilipid layer and peripheral meaning it may protrude from one or both sides
Types of Membrane Proteins
- Receptors: responds to extracellular signals
- Pores/channels/carriers: admit water/transport ions or small molecules/transport large molecules
- Enzymes
- Cell surface proteins: establish self
- Cellular adhesion molecules: enable cells to stick to each other
Cel Adhesion Molecules
proteins which guide the movement of cells
Example of CAM
a white blood cell in the blood stream needs to slow down when it reaches the cut site which happens due to a CAM protein called selectin which coats the white blood cell and provides traction. Another CAM called integrin contacts an adhesion receptor protein in the capillaries near the cut site which protrudes through the capillary space and picks up the slow passing white blood cell
○ Selectin coats WBC and anchor them to capillary walls ○ Adhesion Receptor proteins bind to integrins to help WBC leave the capillary
Integrins(CAM Process)
Integrins: on the surface of WBC which directs them through capillary walls and towards infection site
Effects of Faulty Ion Channels
- Mutations in sodium channels can cause an inability to feel pain
- Mutations in potassium channels can disrupt electrical activity of the heart and impair hearing
- Abnormal Chloride channels are the cause of cystic fibrosis due to clogged pancreas and salty sweat as a result of thick mucus which causes difficulty breathing
- Mutations in potassium channels can disrupt electrical activity of the heart and impair hearing
Endoplasmic Reticulum
a tubular transport system composed of membranous flattened sacs which goes from nucleus towards the cell membrane
○ Works in synthesizing proteins or lipids and either secretes them out of the cell or uses them as the cell membrane grows/repairs
Types of ER
○ Rough: folds proteins into their 3d shapes and ships them to the Golgi
○ Smooth: synthesizes lipids, absorbs fat from the digestive tracts and breaks down certain drugs
- Abundant in liver and skeletal cells
Cytoplasmic Organelles
- ER
- Ribosomes
- Vesicles
- GOlgi
- Mitochondria
- Lysosomes
- ## Peroxisomes
Structure of Mitochondria
- Cristae: Inner folds
- Inner membrane
- Outer membrane
Lysosomes:
contain hydrolytic enzymes which digest proteins, carbs, nucleic acids and bacteria, debris or old cell parts
- Produced in the ER and packaged in the Golgi
Peroxisomes
abundant in liver and kidney cells and contain enzymes called peroxidases which release hydrogen peroxide(H202) to break down cells and catalase to decompose hydrogen peroxide
Function of Enzymes in outside layer of Peroxisomes
○ Synthesis of bile acid used in fat digestion
○ Breakdown of lipids
○ Degradation of rare biochemicals
- Detoxification of alcohol
Cytoplasmic Structures
- Cytoskeleton
- microfilaments
- microtubules
- intermidiate filaments
- centrosomes
- cilia
- flagellum
Microfilaments
tiny rods of actin which form meshwork’s or bundles and provide cellular motility
- E.g. make up myofibrils which shorten or contract muscle cells
- E.g. microfilaments in cell membrane aid in cell motility
Microtubules
long slender tubes of tubulin 2-3x wider than microfilaments which are rigid due to having globular proteins attached in a spiral pattern
- Enables it to maintain cell shapes
- Provide conduits/channel for conveying organelles
Intermediate Filaments
take the general form of dimers(protein pairs) entwined into nested coiled rods which are suited to resist tension
- E.g. intermediate filaments made of keratins are abundant in actively dividing epidermis cells which form a strong inner scaffolding to help cells attach and form a tough protective barrier
Centrosome
a non-membranous structure consisting of two centrioles which are built of microtubules organized as 9 groups of 3
- Migrate to either side of the nucleus in cell division to produce spindle fibers
Cilia
hairlike extensions of the exposed surfaces of cells which move things along the cell surface
- Made of microtubules
- Moves things past the cell e.g. mucus down the respiratory tract
Flagellum
Relatively long, motile process that extends from the surface of a cell and causes it to move
Components of Cell nucleus
- Nucleus is enclosed in a double layered nuclear envelope
○ Inner and outer membranes are joined at places called nuclear pores
§ Pores let our mRNA but not DNA- Nucleolus: a small dense body composed of RNA and protein which has no surrounding membrane and is the site of ribosome production
Chromatin: condensed DNA around histones
Diseases at Organelle Level
- MELAS: mutation in mitochondrial DNA gene preventing someone from extracting enough ATP from nutrients
- Krabbe disease: person cannot produce myelin for nerve cells due to inability to produce on lysosome enzyme
- Tay Sachs disease: swollen lysosomes that lack one of 40 types of enzymes leading to NS failure
- ADL: lack of proteins in peroxisome membranes which leads to a fatty acid build up destroying myelin sheath on nerve cells
Diffusion
moves from areas of high to low concentrations due to the constant motion of substances
- Oxygen, carbon dioxide and lipid soluble substances
Facilitated Diffusion
require protein transporters or ion channels to move substances from an area of high to low concentration
- Non lipid soluble like electrolytes (sodium, potassium, chloride), glucose and amino acids
Osmosis
movement of water through a selectively permeable membrane using aquaporins from areas of high water concentration to low water concentration
Osmotic Pressure
ability of osmosis to generate enough pressure to move a volume of water across a membrane
§ The greater the concentration of impermeant solute particles in a solution, the greater the osmotic pressure of the solution
- Water moves towards solutions with higher osmotic pressure
Tonicity Levels
- Hypotonic: greater osmotic pressure inside the cell, therefore water movement inside the cell, leading to cell swelling
- Hypertonic: greater osmotic pressure in solution, therefore water movement outside the cell, leading to cell shrinkage and crenate
- Isotonic: same concentration as osmotic pressure, therefore not net water movement
Filtration
forcing molecules through a membrane by exerting hydrostatic pressure
○ Commonly used to separate solids from liquids or small particles from large particles
○ E.g. when blood plasma leaves capillaries, water and small solutes leave but large proteins do not coming from the BP
Active Transport
requires carriers/pumps within cell membranes to move from regions of low to high concentration, requiring ATP
○ Carrier proteins are membrane proteins which have specific binding sites for specific particles
○ The addition of ATP changes the conformation shape of the protein shuttling the molecule across the membrane
Endocytosis
molecules too big to enter through diffusion are conveyed in by a vesicle
3 types:
- pinocytosis
- phagocytosis
- receptor mediated endocytosis
Pinocytosis
‘cell drinking’ where cells take in tiny droplets of liquid with dissolved solutes
Phagocytosis
‘cell eating’ takes cells in solids as when particles come into contact with the membrane, a portion of the membrane projects outwards, surrounding the particle, and slowly drawing it inside
§ A phagosome is formed from the cell membrane which surrounds the particle
§ Typically a lysosome will then join to break down the particles into raw materials for the cell
Receptor Mediated Endocytosis
moves specific particles into the cell when the particles(ligands) bind to transmembrane protein receptors, resulting in them being brought in
Exocytosis
the packaging of substances into vesicles which fuse with the cell membrane and are released into the ECF
Transcytosis
when molecules are brought into the cell by endocytosis(receptor mediated), move through the cytoplasm and then are released by exocytosis on the other side
- e.g. transport of HIV across lining of anus or vagina,
Exosomes
a type of vesicle that buds from one cell and moves to and submerges with another cell, transporting substances between cells
○ Play a role in transmissions of diseases
○ Can remove debris, transport immune system molecules and carry both Intracellular and extracellular materials
Stages of Cell Cycle
- Interphase
○ G1
○ S
○ G2 - Mitosis
○ Prophase
○ Metaphase
○ Anaphase
○ Telophase - cytokinesis
Interphase:
- Grows and maintains routine function
- Replication of DNA
- Synthesis of all other parts of membranes, ribosomes, lysosomes, peroxisomes and mitochondria
- Centrioles of centrosome replicate in G2 phase to prepare for mitosis
Karyokinesis
the division of the nuclear contents
Prophase
- Chromatin condense and shorten into chromosomes which are composed of two identical chromatids attached by a centromere due to S replication
- 2 new pairs of centrioles move to opposite sides of the cell and assemble microtubules
- Spindle shaped arrays of microtubules form spindle fibers
- nucleolus breaks apart and nucleus envelope breaks down
Metaphase
- Spindle fibers attach to the centromeres of chromatids so each chromosome is attached by each centriole at different sister chromatids
- Microtubules align chromosomes at midway
Anaphase
- Centromeres of chromatids separate splitting into individual chromosomes
- Spindle fibers shorten pulling chromatids in separate directions to opposite side of the cell
Telophase
- Chromatids elongate back into chromatin
- nuclear envelope forms around each mass of chromatin
- Microtubules of the mitotic spindle disassemble
- Centrioles move back to the nucleus
Cytokinesis
- A cleavage furrow occurs where the cell constricts due to a contractile ring of microfilaments
- Contractile ring of actin filaments forms at right angles to microtubules and attach to the inner surface of the cell membrane
- As the ring pinches it separates the two newly formed nuclei and separates half of the organelles
Factors influencing Frequency and TIming of Mitosis
- Length of telomeres
- Fluctuating levels of kinases and cyclins control cell cycle
- Ratio between surface area of the cell membrane and cell volume
- Hormones and growth factors
- Space availability:
limitation of cell replication due to Telomeres
the same 6 nucleotide sequence at the tip of chromosomes which repeats hundreds of times acts like a candle which breaks down more and more with each mitosis replication, until it reaches a certain point where it inhibits the cell from dividing further.
○ Telomerase enzymes keep telomeres long in cell types which need to continually divide
limitation of cell replication due to Surface area of cell membrane and cell volume ratio
○ The larger the cell, the more nutrients it requires which is limited by its surface area therefore if volume increases faster than surface area, cells can divide to solve the issue
LImitation of Cell replication due to GF and Hormones
○ E.g. hormones can signal mitosis in the lining of the uterus each month, building tissue to support a possible pregnancy
GF function closer to the site of synthesis E.g. epidermal FG stimulates growth of new skin beneath a scab
Limitation of Cell reproduction due to space availability
cells are controlled through density dependent inhibition where healthy cells will not divide if in contact with other cells
different roles of Cancer Mutations
- Driver: provides selective growth advantage
- Passenger: does not cause or propel a cancers growth/spread
Majority in cell are passenger
- Passenger: does not cause or propel a cancers growth/spread
Mutated Genes which can lead to cancer
- Oncogenes: abnormal variants of genes that normally control cell cycle but get overexpressed
tumor suppressor genes: when inactivated it lifts control of cell cycle leading to uncontrolled replication
Cell Differentiation
guides cell specialization by activating and suppressing functions of many genes
Stem Cells
cells which have the ability to divide repeatedly without specialization, allowing for continual growth and renewal
- Divides mitotically to yield two identical daughter cells with which 1 remains a stem cell and the other partially specializes
Self Renewal
the ability of a stem cell to divide and give rise to at least one other stem cell
Progenitor
a partly specialized cell that is the daughter of a stem cell
- Said to be committed because its daughter cells can only become any of a restricted number of cell types
○ E.g. a neural progenitor cell cannot give rise to muscle cells
Terms for cells based on their replication potential
Totipotent: daughter cells can specialize as any cell type
- Given to fertilized egg cells and early embryo cells
Pluripotent: daughter cells can specialize into several pathways but not all
- Given to progenitor cells
Types of Cell Death
Apoptosis: programed cell death to prevent further harm/damage
- Caspase enzymes are activated where they cut up certain cell components
Necrosis: cell death resulting from damage
