Cells Flashcards
What are the three main regions of a cell?
Cell membrane, nucleus, cytoplasm
What is the organized mesh that holds cells together?
Extracellular matrix
Describe the extracellular matrix.
Gelatinous substance composed of proteins and carbohydrates
Fluids make up what percentage of body mass in women and what percentage in men?
55% in women, 60% in men
What percentage of human body fluid is intracellular?
67%
What is the fluid mosaic model?
A model of the plasma membrane depicting a phospholipid bilayer with integral proteins.
What is the main function of extracellular fluid (ECF)?
Dissolve and transport substances
What is the function of interstitial fluid?
Surrounds and bathes cells in tissues; contains amino acids, sugars, fatty acids, regulatory substances, and wastes. Cells must extract from this mix the exact amounts of substances they need.
What molecule makes up 20% of the plasma membrane’s lipids and provides structure to the membrane?
Cholesterol
What are peripheral proteins?
Proteins that are not embedded in the plasma membrane but lie adjacent to the cytoplasmic side of it, helping to support it. They attach loosely to integral proteins or anchor to the plasma membrane.
What is the glycocalyx?
The fuzzy, sticky, carbohydrate-rich area at the cell surface composed of glycoproteins and glycolipids
What cell feature is unique to each type of cell and helps to serve as an identity molecule for cell to cell recognition?
The glycocalyx
What kind of cell junction involves a series of occludins that fuse to form an impermeable junction that prevents molecules from passing through? Where is this type of junction found?
Tight junction; between epithelial cells of the digestive tract
What type of cell junction involves the mechanical coupling of cadherins to prevent cell separation? Where would you find this type of junction?
Desmosomes; abundant in the skin and in heart muscle, which are both subjected to great mechanical stress
What type of cell junction involves connection via hollow cylinders called connexons? Where are these junctions found?
Gap junctions; in electrically excitable tissue such as heart and smooth muscle
What molecules is the plasma membrane permeable to?
Nonpolar molecules such as oxygen, carbon dioxide, and steroids, as well as small polar molecules such as water
What molecules is the plasma membrane impermeable to?
Large polar molecules such as glucose and ions (Na+, K+, Cl-)
What is resting membrane potential?
The potential difference across a cell membrane due to separation of oppositely charged particles on either side.
Where does voltage due to resting membrane potential occur in the cell? Why does it only occur there?
Only at the membrane surface because the rest of the cell and the extracellular fluid are neutral.
What is the difference between a chemical gradient and an electrical gradient?
Chemical gradient refers to the concentration gradient (high to low) while the electrical gradient refers to the potential of ions to cross membranes (positive to negative)
Potassium moves out of the cell due to its __________ gradient and into the cell due to its _________ gradient.
Chemical, electrical
What kinds of solutes move through the plasma membrane via facilitated diffusion?
Some ions, some amino acids, and monosaccharides
What are two types of facilitated diffusion?
Channel-mediated and carrier-mediated
What channels are always open and allow ions or water to move according to concentration gradients?
Leakage channels
What channels open or close due to changes in chemical or electrical gradients?
Gated channels
What are aquaporins?
Transmembrane proteins that construct water-specific channels in the plasma membrane that allow single-file diffusion of water molecules
Where are aquaporins abundant?
Red blood cells, kidney tubule cells, and other cells involved in water balance
What term describes the total concentration of solute particles in a solution?
Osmolarity
What is hydrostatic pressure?
The “pushing” force on water due to the presence of more fluid in one region than another (pushes water out of a cell)
What is osmotic pressure?
The “pulling” force on water due to the presence of solutes in solution (draws water into the cell)
What is tonicity?
The ability of a solution to change the shape of cells by altering the cell’s water volume
What happens to a cell when it is placed in a hypotonic solution?
Swelling and lysis
What happens to a cell when it is placed in hypertonic solution?
Crenation
What is the difference between osmolarity and tonicity?
Osmolarity is based on the total solute concentration, tonicity is based on both concentration and solute permeability of the plasma membrane
What is primary active transport?
Transport of a molecule across the plasma membrane directly driven by hydrolysis of ATP by transport proteins called pumps
What is secondary active transport?
Transport across the plasma membrane driven by energy stored in concentration gradients of ions created by the primary active transport pumps. Always move more than one substance at a time.
Describe the action of the sodium-potassium pump.
1 molecule of ATP drives 3 sodium ions out of the cell and two potassium ions into the cell
Describe the mechanism of secondary active transport. What is its source of energy?
Uses a cotransport protein to couple the downhill movement of one solute to the uphill movement of another. The electrochemical gradient created by primary active transport is its source of energy.
What is a symport system? What is an example of this?
Two transported substances being moved through a pump in the same direction; sodium diffusion assisting glucose into the cell via a cotransporter protein
What is an antiport system? What is an example of this?
Transported substances move through a membrane in opposite directions; sodium/hydrogen ion cotransporter uses the sodium gradient to pump hydrogen out of the cell
What is transcytosis? Where is this type of transport commonly found?
Vesicular transport that moves substances through a cell membrane from one side to the other; common in epithelial cells lining blood vessels
What is vesicular trafficking?
A vesicular transport that moves substances from one area to another; energized by ATP or GTP
What are three types of endocytosis?
Phagocytosis, pinocytosis, and receptor-mediated endocytosis
What is the main mechanism for specific endocytosis and transcytosis of most macromolecules by body cells?
Receptor-mediated endocytosis
_________ causes ionic imbalances that polarize the membrane, while ___________ maintain that membrane potential.
Diffusion; active transport processes
Resting membrane potential is maintained mainly by what two things?
The concentration gradient of potassium and the differential permeability of the plasma membrane to potassium and other ions
What charged molecules and ions predominate inside of the cell?
Potassium cations and protein anions
Why does the inside of the cell have an overall negative charge?
The plasma membrane is somewhat permeable to K+ via leakage channels, but is impermeable to the protein anions that predominate within the cell
Which way does the concentration gradient of potassium go?
Out of the cell
Which way does the electrical gradient of potassium go?
Into the cell
What is the membrane potential when the concentration gradient promoting potassium exit exactly opposes the electrical gradient promoting potassium entry?
-90 mV
Why doesn’t chloride contribute to the resting membrane potential of the cell?
It’s concentration and electrical gradients exactly balance each other out
What effect does sodium’s strong attraction to the cell’s interior by both its concentration and electrical gradients have on the resting membrane potential?
Reduces it to -70 mV
Why doesn’t sodium have a larger effect on the resting membrane potential?
The membrane is much more permeable to potassium than to sodium
What would happen to the ions on either side of the plasma membrane if only passive forces were at work?
They would eventually reach equilibrium and the electrochemical gradient would be neutralized
What pump plays the largest role in maintaining membrane potential?
Sodium-potassium pump
What are cell adhesion molecules and what are they made of?
Cell surface components that anchor cells, allow cells to migrate, provide SOS signals, and act as mechanical sensors of the ECM, initiating cellular responses to changes; they are made of glycoproteins
What receptor exerts its effect indirectly through a specific protein and acts as a middleman to activate or inactivate membrane-bound enzymes or ion channels, generating intracellular chemical signals and connecting plasma membrane events to internal metabolic activity?
G protein-coupled receptor
What are two important second messengers that participate in intracellular signaling? What do they typically activate?
Cyclic AMP and ionic calcium; typically activate protein kinase enzymes which transfer phosphate groups from ATP to other proteins
Describe the inner membrane of the mitochondria.
Folds inward, forming cristae that protrude into the mitochondrial matrix, and has membrane-bound enzymes
What do the enzymes embedded in the mitochondrial cristae do?
Participate in aerobic cellular respiration by breaking down intermediate products to water and carbon dioxide. Captures released energy for phosphate group attachment to ADP.
What do free ribosomes make?
Soluble proteins that function in the cytosol or are imported into other organelles
What do membrane-bound ribosomes make?
Proteins destined for incorporate into cell membranes or lysosomes, or for export from the cell
What does the rough endoplasmic reticulum do?
Synthesizes all proteins secreted from cells, as well as phospholipids and integral proteins that form the plasma membrane.
Where does lipid synthesis occur in the rough endoplasmic reticulum?
On the cytosolic face
What does the smooth endoplasmic reticulum do?
Metabolizes lipids, synthesizes cholesterol and phospholipids, steroid-based hormones, detoxifies drugs and chemicals, breaks down stored glycogen to form glucose, stores calcium ions
What does the Golgi apparatus do?
Modifies, concentrates, and packages cellular proteins and lipids made in the rough ER for export out of the cell
What three types of vesicles bud off of the Golgi apparatus? What part of the Golgi do they bud from?
Secretory vesicles that carry proteins for secretion, vesicles carrying membrane components, and lysosomes that carry digestive enzymes. These vesicles bud off of the trans face of the Golgi.
What enzymes do peroxisomes contain? What is their purpose?
Oxidases and catalases; neutralize free radicals
Where are peroxisomes most abundant?
Liver and kidney cells
What types of cells are lysosomes most abundant in?
Phagocytes
How does a lysosomal membrane maintain the pH within its boundaries?
Contains H+ pumps and ATPases that gather hydrogen ions from the cytosol to maintain acidic pH
What are the functions of a lysosome?
Digests particles, degrades stressed or dead cells and nonfunctional organelles, breaks down and releases glycogen, breaks down bone to release calcium ions
What organelles are included in the endomembrane system?
ER, Golgi, secretory vesicles, lysosomes, and the nuclear envelope
What are the thinnest cytoskeleton elements, made of semi-flexible strands of actin?
Microfilaments
What are the functions for microfilaments?
Cell motility, changing and maintaining cell shape, distributing tension
Which cytoskeletal rod is responsible for cleavage furrows and amoeboid motion?
Microfilaments
What are the tough, insoluble protein fibers that are made of twisted units of tetramer fibrils called?
Intermediate filaments
What are some functions for intermediate filaments?
Attachment to desmosomes, resistance of pulling forces exerted on the cell
What is the most stable and permanent of the cytoskeletal elements?
Intermediate filaments
What cytoskeletal element is made of hollow tubes made of tubulin?
Microtubules
Where do most microtubules radiate from?
The centrosome
What are the functions for microtubules?
Determine overall cell shape and organelle distribution, framework for motor proteins to move organelles and molecules around the cell
Each centriole consists of a pinwheel array of ____ _____ of microtubules.
Nine triplets
What forms the basis of flagella and cilia?
Basal bodies
What are the motor proteins attached to cilium doublets called?
Dynein arms
What are cytoplasmic extensions that increase surface area and aid in absorption called? What are they made of?
Microvilli; Actin filaments
What is the inner membrane of the nuclear envelope lined by? What is it made out of?
The nuclear lamina, a network of rod-shaped proteins assembled to form intermediate filaments
Where are ribosomal subunits assembled?
Nucleoli
Describe the composition of chromatin.
30% DNA, 60% histone proteins, 10% newly formed or forming RNA chains
What are nucleosomes?
Fundamental units of chromatin: DNA wound around clusters of eight histone proteins
What would you find on histone proteins in non dividing cells?
Methyl groups
What would you find on histone proteins in dividing cells?
Acetyl groups
What is the period from cell formation to cell division, during which all routine activities are carried out?
Interphase
What subphase of interphase includes ample metabolic activity and concludes when the centrioles have started to replicated?
G1 phase
During what interphase subphase does DNA replicate?
S phase
What enzymes are activated or deactivate by proteins and initiate cascades essential for cell division?
Cyclin-dependent kinases (activated and deactivated by cyclin proteins)
During what interphase subphase are enzymes and other proteins needed for division synthesized and centriole replication completed?
G2 phase
What must occur before the cell officially enters mitosis?
A successful G2/M phase checkpoint revealing no need for further DNA replication or repair
What enzyme forms the new complementary strands of DNA during replication?
DNA polymerase
Name the mitosis phase: chromosomes become visible, nucleoli disappear, and a spindle forms as microtubules lengthen from the centrosomes.
Early prophase
Name the mitosis phase: nuclear envelope breaks down, kinetochore microtubules attach to kinetochores at the centrosomes, nonkinetochore microtubules force the poles apart, and chromosomes begin to move to the midline.
Late prophase
Name the mitosis phase: chromosomes are aligned at the spindle equator and are each attached to kinetochore microtubules. Enzymes begin separating sister chromatids.
Metaphase
Name the mitosis phase: shortest phase, enzymes complete sister chromatid separation and the microtubules pull the chromosomes to either pole. Nonkinetochore microtubules lengthen to push the poles apart.
Anaphase
Name the mitosis phase: begins when migration to the poles of the cell has been completed, chromosomes begin to uncoil, a new nuclear envelope forms, and nucleoli reappear. The spindle breaks down.
Telophase
What is the term used to describe the division of the cytoplasm that begins during late anaphase?
Cytokinesis
What is the contractile ring that creates the cleavage furrow made of?
Actin filaments (microfilaments)
Describe the initiation phase of transcription.
Transcription factors bind to the promoter of the gene after they have stimulated histones to loosen. RNA polymerase initiates transcription.
Describe the elongation phase of transcription.
RNA polymerase moves along the template strand, adding RNA nucleotides to the growing mRNA strand
During what phase of transcription would you find a DNA-RNA hybrid?
Elongation
Describe the termination phase of transcription.
Synthesis ends when RNA polymerase reaches a termination signal in the template strand and mRNA is released.
What must happen to the completed pre-mRNA prior to its exit from the nucleus?
Spliceosomes must remove introns and splice together exons (mRNA processing)
Where does an mRNA:ribosome complex go if a short leader peptide called an ER signal sequence is detected in the protein being synthesized?
To the rough ER for processing
What guides the mRNA:ribosome complex to the rough ER?
A signal recognition particle on the growing polypeptide.
What pathway disposes of individual proteins that are misfolded, damaged, or unneeded?
Ubiquitous-proteasome pathway
What are ubiquitins?
Proteins that attach to other proteins, marking them for destruction by proteasomes
