Chapter 3: Cells - The Living Units Flashcards
What are Extracellular materials?
- Extracellular fluid
- Cellular secretions
- Extracellular matrix
What is Extracellular fluid?
Includes interstitial fluid, blood plasma, and cerebrospinal fluid.
ECF dissolves and transports substances. Includes amino acids, sugars, fatty acids, regulatory substances, and wastes.
What are cellular secretions?
Includes substances that aid in digestion and some act as lubricants
What is Extracellular matrix?
The most abundant Extracellular material. Most cells are in contact with jellylike substance made of proteins and polysaccharides. Cells secrete, and it is an organized mesh in the Extracellular space.
How much of the plasma membrane is made of cholesterol?
About 20% of the plasma membrane. It makes the membrane stiffer
What are the kinds of membrane proteins?
- Transport
- Receptors for signal transduction
- Enzymatic activity
- Cell-cell recognition
- Attachment to the cytoskeleton and ECM
- Cell to cell joining
What are the three kinds of cell junctions?
Tight junctions
Desmosomes
Gap Junctions
What do tight cell junctions do?
A series of integral protein molecules that fuse together like ZipLock. Forms an impermeable junction.
What do desmosomes cell junctions do?
These serve as anchoring junctions — mechanical couplings like rivets. On the inside of the cell, it has a button like thickening called plaques. Cells are held together by protein filaments (cadherins) and extracellularly by keratin filaments (part of the cytoskeleton) extend within the cell to hold it together.
What are gap junctions?
Allows selective communication between cells.
What is diffusion?
Movement of molecules or ions from an area of high concentration to an area of low concentration.
What is osmosis?
Movement of H2O from low concentration to high concentration.
What determines whether a given substance can cross the plasma membrane?
Lipid solubility and Size
However, small molecules can diffuse across if not lipid soluble, and other molecules can be transported by carrier molecules such as an ion channel or transport protein
What is tonicity?
This refers to the ability of a solution to change the shape (or plasma membrane tension) of cells by altering the cells’ internal water volume (tono = tension)
Isotonic means both solutions are the same and cells retain their normal shape
Hypertonic means the Extracellular solution has a higher concentration of non penetrating solutes, and thus the cell loses water
Hypotonic means the cytoplasm has lower concentration, and thus the cell takes on water and can burst
What is the difference between osmolarity and tonicity?
Osmolarity is based SOLELY on its total solute concentration. In contrast, Tonicity is based on how the solution affects cell volume, which depends on (1) solute concentration and (2) solute permeability of the plasma membrane.
What is the definition of primary active transport?
The process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP using transport proteins called “pumps”
Define Secondary Active Transport
Driven by energy stored in concentration gradients of ions created by primary active transport pumps. Secondary active transport systems always move more than one substance at a time using a contransport proteins)
What are the two types of Vesicular Transport?
Endocytosis, exocytosis
Also transcytosis (moves substances into, across, and then out of the cell) common in endothelium cells
And Vesicular trafficking, which moves substances from one area in the cell to another.
What defines endocytosis? What are the three kinds?
Is the main way the cell brings in bulk solids, most macromolecules, and fluids (or transporting them across).
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
What is phagocytosis?
“Cell eating”
The cell engulfs relatively large or solid material (such as clump of bacteria, cell debris)
Uses pseudopods to envelop.
Forms “phagosome”
Most cases, fuses with a lysosome to be digested
Often white blood cells
What is Pinocytosis?
“Cell drinking”
Infolding plasma membrane surrounds a very small volume of Extracellular fluid containing dissolved molecules.
It is a routine function in most cells.
A non selective way of sampling Extracellular fluid.
Membrane absorbed is recycled back to the plasma membrane
What is receptor mediated endocytosis?
The main mechanism for specific endocytosis and transcytosis of most macromolecules. Endocytosis mediated by protein receptors.
What is exocytosis?
“Exporting” products or waste.
Vesicles have v-snares that bind to t-snares on the plasma membrane and release their contents.
What is the typical resting membrane potential?
-50 to -90 millivolts (mV)
What composes the cytoplasm?
The cytosol - viscous fluid in which other cytoplasmic elements float.
Inclusions - chemical substances that may or may not be present depending on the cell type (stored nutrients, glycogen granules, lipid droplets, and pigment granules)
Organelles - machinery of the cell.
What is the mitochondria and what does it do?
Provides most of ATP supplies. Kidney and liver cells have hundreds of mitochondria.
Enclosed by 2 membranes: outer and inner which folds inward, forming shelf-cristae that protrude into the matrix (gel substance).
Enzymes in it break down products of food (glucose and others) to water and carbon dioxide.
Some of this energy is captured in ATP (ADP + phosphate group)
What are ribosomes and what do they do?
Two subunits that fit together. Sites of protein synthesis dictated by RNA (from DNA).
Can be free or bound to rough ER
What is endoplasmic reticulum (ER) and what does it do?
An extensive system of interconnected tubes and parallel sacs (cisterns).
Rough ER and smooth ER
Rough ER has ribosomes. The Rough ER takes the amino acid chain and finishes folding it, then send it to the Golgi apparatus
Also manufactures phospholipids for the cell membrane
Smooth ER (no ribosomes) metabolizes lipids (synthesize other lipids) synthesizes steroid based hormones, detoxifies drugs, breaks down glycogen to form free glucose (especially liver), stores calcium ions
What is the Golgi apparatus and what does it do?
Its main job is to modify, concentrate, and package the proteins and lipids made at the rough ER and destined for export from the cell.
What are peroxisomes and what do they do?
Resembling small lysosomes, they contain powerful enzymes (oxidases and catalases)
Especially numerous in kidney and liver cells.
What are lysosomes and what do they do?
Spherical membranous organelles that contain hydrolytic (digestive) enzymes.
Large and abundant in phagocytes. Can digest almost all kinds of biological molecules. Can be called acid hydrolases
Digests particles
Degrades stressed or dead cells (autophagy)
Preforms metabolic functions (breaking down glycogen)
Breaks down bone to release calcium.
What is the endomembrane system and what does it do?
System of organelles that 1: produce, degrade, store, and export biological molecules, and 2: degrade harmful substances. Includes ER, Golgi, secretory vesicles, and lysosomes, as well as nuclear envelope.
What are the three types of “rods” that make up the cytoskeleton? What do they do?
- Microfilaments - made of spherical protein subunits called actin. Flexible. Involved in cell motility. Can often break down and reform, changing cell shape. can pinch one cell into two (cell division). In muscle cells, they act with myosin to generate contractile forces.
- Intermediate filaments - Tough, insoluble protein fibers like woven ropes. Made of twisted subunits “tetramer fibrils”. Most stable of the types.
- Microtubules - largest diameter. Hollow tubes made of spherical protein subunits called “tubular”. Most radiate from small region near the nucleus called “centrosome” remarkably dynamic
What is the centrosome and centrioles? What do they do?
Anchor microtubules
What are cilia?
Whiplike, motile cellular extensions that occur in large numbers on exposed cell surfaces. Moves substances in one direction.
When about to form, centrioles multiply and line up and “sprout” / extend membrane outward.
What are flagella?
Only on sperm, projections by centrioles that propel the sperm.
What are microvilli?
Tiny, finger like extensions of the plasma membrane from an exposed cell surface. Increase plasma membrane surface tremendously mostly on absorptive cells.
What is chromatin?
Composed of 30% DNA
60% Histone proteins (package/bind together)
10% RNA chains, newly formed or forming.
What is a nucleosome?
Eight histone proteins wrapped by 2 winds of the DNA double helix
What are the two major periods of the cell cycle?
Interphase - cell grows and carries on its usual activities
Cell division (multicultural phase) - cell divides into two cells
What is Interphase? What are its sub phases?
The period from formation to division. (Metabolic or growth phase)
G1 (growth)
S (Growth and DNA synthesis)
G2 (Growth and final preparations for division
What is the G1 phase? (Gap 1)
Cell is metabolically active, synthesizing proteins and growing. Most variable in terms of length of time. Can last from minutes to years.
What is S phase of Interphase?
DNA is replicated. New histones are made and assembled into chromatin.
What is the G2 phase of Interphase?
The final phase of Interphase - brief. Enzymes and other proteins needed for division are synthesized and moved to proper sites. By the end of the phase, centrioles replication is complete.
G2/M checkpoint, when cell ensures that all DNA is replicated and repaired.
What are the two events in the M (mitotic) phase?
Mitosis and cytokinesis
What happens in the Mitotic phase?
The nucleus divides. Divided into Prophase, metaphase, anaphase, and telophase.
How is cell division regulated?
Both internal and external factors.
Ratio of cell surface/cell wall. As cell grows, volume increases more rapidly than surface area. Bigger cells need more nutrients. This limits how big a cell can be.
Chemical signals such as growth factors and hormones.
Availability of space. Cells often stop replicating when they begin touching. (Contact inhibition)
How does the book define genes?
A segment of DNA that carries instructions for creating one polypeptide chain. We have 20,000 specific genes.
What are the four nucleotide bases?
A, G, T, and C
What are Exons?
The sections of DNA that code for proteins.
Introns are long intervening sequences that serve as control elements
What nucleotide bases does RNA have?
A, G, U, and C
U replaces T(in DNA)
What are the three types of RNA?
Messenger RNA (mRNA) - Carries DNA info to be synthesized
Ribosomal RNA (rRNA) - forms the ribosomes
Transfer RNA (tRNA) - connect amino acids to the polypeptide chain based on DNA info
What happens in Prophase (Mitosis)?
Chromatin coils to form Chromosomes
Nucleoli disappears
Two centrosome separate and act as focal points for growth of a microtubule assembly (mitotic spindle) that propel centrosome in opposite directions.
What happens at the end of Prophase (1st phase of Mitosis)?
Nuclear envelope breaks up, allowing the spindle to interact with the chromosomes
Spindles (kinetochore microtubules) attach to center of chromosomes
Other spindles (nonkinetochore microtubules) slide past each other forcing the poles apart
Kinetochore microtubules pull on each other which draws the chromosomes to the center
What happens in Metaphase (mitosis)?
Two centrosome are at opposite poles
Chromosomes are aligned in the center (metaphase plate)
At the end, enzymes to separate the chromatids are activated
What happens in Anaphase (mitosis)?
This is the shortest phase. Chromosomes split into chromatids
Kinetochore microtubules shorten, pulling each chromosome toward the pole it faces
Nonkinetochore microtubules lengthen and push two poles apart
What happens in Telophase/Cytokenesis (mitosis)?
Sets of chromosomes at opposite ends of the cell uncoil and resume their threadlike chromatin form.
New nuclear envelopes form around each chromatin mass. Nucleoli reappear.
The spindle breaks down and disappears
Mitosis ends, the cell is briefly “binucleate” and each is identical
Cytokinesis begins during anaphase and continues beyond telophase, actin microfilaments form a furrow that pinches the cell apart.
What is a codon?
The three-nucleotide base that determines specific amino acids. Three call for “stop”
What is the start codon? What are the stop codons?
Star: AUG
Stop:
UAA
UAG
UGA
What are the three events of RNA translation?
Initiation
Elongation (codon recognition and then peptide bond formation and then translocation
Termination
What is the process of Rough ER processing of proteins (image)?
