Chapter Three Flashcards
1
Q
Fluid mosaic model
A
- A continually moving “sea” of fluid lipids that contain a mosaic of many different proteins.
- Some proteins float freely like icebergs.
- Others are anchored at specific locations.
2
Q
Plasma membrane function
A
- Surrounds and protects the cell
- Controls the flow of substances in and out of the cell (semi-permeable)
- Participates in cell signaling
- Provides attachment to other cells
3
Q
Plasma Membrane Structure
A
- Lipid bilayer arrangement - 2 back-to-back layers made up of 3 types of lipids:
-
Phospholipids have polar and non-polar parts
- Polar heads face outward and are hydrophilic
- Non-polar tails face inward (towards each other) and are hydrophobic
- Cholesterol is a structural component that helps hold the phospholipids together.
-
Glycolipids are only found in the layer that faces the extracellular fluid.
- Act in cell signaling
4
Q
What are the two types of membrane proteins?
A
- Integral (transmembrane) proteins
- Peripheral proteins
5
Q
Ion channel
A
Allow certain ions to pass in and out of the cell
integral
6
Q
Carrier Proteins
A
Transport specific substances across the membrane
integral
7
Q
Receptor proteins
A
Bind to specific substance to cause change in cell
integral
8
Q
Enzyme
A
act as catalysts to speed up cellular processes
Integral and peripheral
9
Q
Linker protein
A
helps cells attach to other cells
integral and peripheral
10
Q
Cell identity marker
A
distinguishes your cells from anyone else’s
glycoprotein
11
Q
Membrane fluidity and permeability
A
- The cell membrane is a fluid structure
- Most membrane lipids and proteins can move easily in the bilayer
- Cholesterol is embedded within the membrane.
• Serves to stabilize the membrane and reduce fluidity.
• Makes the membrane less permeable to very small water-soluble molecules - Cell membranes are selectively permeable
• Allows small non-polar, uncharged molecules to pass through
• The proteins help polar, charged molecules to pass through
• Macromolecules (too large) can only pass through by endocytosis and exocytosis.
12
Q
Concentration and electrical gradients
A
- Concentration (chemical) gradient
• Difference in the concentration of a chemical between one side of the membrane and the other. - Electrical gradient
• Difference in the concentration of ions between one side of the membrane and the other.
• Responsible for the “Membrane Potential”
• Inside of the cell is more negative - Together the 2 gradients make up the electrochemical gradient.
• Most chemicals and ions will move down their gradient.
• From an area of high concentration to an area of lower concentration until equilibrium (balance) is achieved.
13
Q
Passive processes
A
- no energy required
- simple diffusion
- facilitated diffusion
- osmosis
14
Q
Active processes
A
- requires energy
- vesicular transport
15
Q
Simple Diffusion
A
- Caused by the random motion of molecules.
- Involves the movement of molecules from an area of greater concentration to an area of lower concentration:
- Until equilibrium is reached and molecules are more evenly distributed (diffuse).
- Diffusion of a substance across a membrane can happen only if:
1. The membrane is permeable to that substance.
2. A concentration gradient exists (concentration of the substance is higher on one side of the membrane than the other).
16
Q
Facilitated diffusion
A
- Used to transport solutes that are too polar or charged to move through the membrane by simple diffusion.
- Similar to simple diffusion in that molecules move from areas of higher concentration to lower concentration.
- Uses membrane proteins that function as channels or as carriers.
• Allow molecules to move across cell membrane.
• The number of carrier or channel proteins in the cell membrane limits the rate of this process.
• Examples:
• K+ channels
• Glucose transporters - The number of carrier proteins available on the plasma membrane determines the rate of facilitated diffusion.
• More carrier proteins = increase rate
• Once all of the carriers are occupied, transport maximum is reached.
• Similar to a completely saturated sponge.
17
Q
Facilitated diffusion of glucose
A
• Glucose is the body’s preferred energy source for making ATP.
• Enters the body’s cells through facilitated diffusion.
• The hormone insulin causes the cell to insert more glucose
carrier proteins into the cell membrane.
• Allows the cell to pick up glucose more rapidly from the blood.
• What happens if the body can no longer utilize or produce
insulin?
• Diabetes Mellitus
18
Q
Osmosis
A
- Osmosis = diffusion of water across a selectively permeable membrane.
• From an area of higher water concentration to an area of lower water concentration
• Membrane is permeable only to water – not solutes - Osmotic pressure
• Pressure created by the concentration of solutes (lack of water) on one side of a membrane.
• Higher osmotic pressure = more impermeable solutes, less water
• Lower osmotic pressure = less impermeable solutes, more water - Remember: water will move down its concentration gradient
• Moves from area of low osmotic pressure (more water) to high osmotic pressure (less water).
• To make solutes less concentrated
19
Q
Tonicity
A
measure of a solution’s ability to change the volume of cells by
altering their water content
20
Q
Isotonic solution
A
- concentration of water and solutes is same on outside and inside.
• No change - Equal amounts of water move in and out - no change to the cell
21
Q
Hypertonic Solution
A
- solution has higher osmotic pressure
• Greater concentration of solutes outside cell
• Water moves out of cell into surrounding solution = cell shrinks (crenation). - Water moves out of the cell – cell shrinks (crenation)
22
Q
Hypotonic Solution
A
- solution has lower osmotic pressure
• Lower concentration of solutes outside cell
• Water moves into cell = cell swells and can burst (cytolysis) - More water moves into the cell – cell swells and can burst (hemolysis)
23
Q
Active transport
A
- Used to move substances against their concentration or electrical gradient.
• From an area of low concentration to an area of higher concentration. - Requires energy (ATP)
• Often uses proteins as “pumps”.
• Example: The sodium-potassium pump (Na+-K+ATPase - Energy derived from ATP changes the shape of a transporter protein which pumps a substance across a plasma membrane against its concentration gradient
24
Q
Transport in vesicles (endocytosis vs exocytosis)
A
- Endocytosis
• The cell membrane wraps around a large particle to form a vesicle (phagocytosis)
• Phago- = to eat
• The vesicle moves the particle into the cell to be used or destroyed.
• Example = a white blood cell engulfs a bacteria cell to destroy it. - Exocytosis
• The opposite of endocytosis
• Vesicle containing a particle docks with inside of membrane
• Membrane opens up to release particle
25
Cytoplasm
* Consists of all the cellular contents between the plasma membrane and the nucleus
* 2 components:
* Cytosol (intercellular fluid)
* Organelles
* Cytosol is the fluid portion of cytoplasm that makes up about 55% of the total cell volume
* mostly water plus various dissolved and suspended components
* Most cell activities occur in the cytoplasm where nutrients are received, processed, and stored
* Organelles have specific functions
26
Endoplasmic Reticulum (ER)
* A network of membranes in the shape of flattened sacs or tubules
* provides tubular transport system inside the cll
* participates in the synthesis of protein and lipid molecules
* 2 types:
* Rough ER: studded with ribosomes, synthesizes glycoproteins and phospholipids
* Smooth ER: no ribosomes, synthesizes fatty acids and steroids
27
Ribosomes
* site where protein synthesis occurs
* composed of 2 subunits- protein and rRNA
* Can be attached to the ER or scattered throughout the cytoplasm
28
Golgi Complex
* Composed of flattened sacs.
* Refines, packages, modifies, and delivers proteins.
* Proteins from the ER arrive at the Golgi enclosed in vesicles.
* Vesicles fuse with Golgi apparatus, and the contents are modified.
* The modified proteins are released from the Golgi in transport vesicles.
* The transport vesicles can move to and fuse with the cell membrane to release its contents to the outside of the cell (exocytosis).
29
Mitochondria
* Energy producer for the cell
* Produce and store ATP through aerobic respiration.
* ATP is what cells use for energy.
* Very active cells such as muscle cells contain many thousands of mitochondria.
* Mitochondria can divide (replicate) and contain their own DNA.
• Mitochondrial DNA (mtDNA) is passed on from mother to offspring.
• Can be used to trace maternal lineage.
30
Lysosomes
* “garbage disposals” of the cell
* Tiny membranous sacs that contain enzymes that break down old cell components and bacteria
31
Peroxisomes
* localized to liver and kidney cells
* contain enzymes that function in the synthesis of bile acids, breakdown of lipids, and detoxification of alcohol
32
Microfilaments and Microtubules
* Thin, threadlike structures that serve as the cytoskeleton of the cell.
* Microfilaments – rods of proteins that can move and flex to provide the cell with movement.
* Microtubules – tubes of proteins that are important in
cell division.
33
Centrosome
* Structure near the Golgi apparatus and nucleus.
* Made up of 2 cylinders called centrioles.
* Help form and organize microtubules.
* Functions in the separation of chromosomes during cell division.
34
Cilia and Flagella
* Motile extensions from the cell surface.
* Cilia help move substances across cell surface.
* Flagella help cell to propel the cell (sperm cells).
35
Vesicles
* Membranous sacs that store or transport substances within a cell.
* Formed either from the cell membrane, the endoplasmic reticulum, or the Golgi apparatus.
36
Nucleus
* Largest organelle in the cell.
• Surrounded by a nuclear envelope.
• Contains nuclear pores that allow the passage of certain substances.
* Nucleus contains the following structures:
• Nucleolus – dense body composed of RNA and protein.
• Chromatin – consists of loosely coiled fibers of protein and DNA.
* During cell division chromatin condenses to form structures called chromosomes.
37
Protein Synthesis
* A large part of a cell’s function is determined by its shape.
* Much of a cell’s shape is formed from proteins.
* Most of the cell’s activities are devoted to synthesizing various proteins.
* Proteins are formed by connecting amino acids in particular orders.
* The order in which amino acids are connected is determined by the genetic “code”.
* Gene expression is the process of using DNA as a template for the synthesis of a specific protein.
* Protein synthesis consists of 2 processes:
* Transcription
* Translation
38
Transcription
* Occurs in the nucleus
* Genetic information from DNA is copied into RNA.
* A specific section of DNA is unraveled to expose nucleotides.
* DNA Nucleotides = A, T, C, G
* RNA nucleotides pair up with DNA nucleotides
* RNA Nucleotides = A, U, C, G
* The newly formed mRNA strand moves out of the nucleus and attaches to a ribosome.
* mRNA = messenger RNA
* The code for each amino acid is represented as a triplet of nucleotides (codon)
* Example: CAG
39
Translation
* Translation = mRNA →protein
* Occurs in ribosomes
* mRNA codons pair up with tRNA anticodons
* tRNA = transfer RNA
* Example = CAG →GUC
* Each anticodon triplet carries a specific amino acid.
* GUC = amino acid A
* AUG = amino acid B
* The order of mRNA codons determines the order of tRNA anticodons, which determines the order of amino acids.
* As the amino acids are joined, they assemble to form a new protein molecule.
40
Cell Division
* Process in which cells reproduce themselves
* The cell cycle is a series of changes a cell undergoes from the time it is formed until it reproduces.
* Consists of 2 key periods:
* Interphase – when a cell is not dividing
* Mitotic phase (mitosis) – when a cell is dividing
41
Interphase
* A period of great metabolic activity.
* Cell grows and synthesizes new molecules and organelles.
* Interphase can be broken into different phases.
* S-phase – DNA is replicated in preparation for cell division (synthesis phase).
* G1 and G2 phases – cell grows and other structures are duplicated (growth phase).
42
Prophase
* First stage of mitosis.
* DNA (chromatin) condenses into paired chromosomes.
* Centrioles migrate to poles.
* Microtubules organize into spindle fibers.
* Nucleolus and nuclear envelope disappear.
43
Metaphase
* Spindle fibers attach to centromeres on chromosomes.
* Chromosomes align at center of the cell (metaphase plate).
44
Anaphase
* Centromeres split.
* Identical sets of chromosomes move to opposite poles of the cell.
* Beginning of cytokinesis\*
45
Telophase
* Nuclear envelope and nucleolus begin to reappear.
* Chromosomes disperse into chromatin.
46
Cytokinesis
* Cytoplasmic division
• Begins in late anaphase.
• Continues as a contractile ring (cleavage furrow) that pinches the two new cells apart.
• The two daughter cells contain identical genetic information.
• When cytokinesis is complete, interphase begins.
47
Somatic vs. Germ cells
* Somatic cells = any cell of the body other than a germ cell.
* All go through mitosis
* Result is 2 daughter cells with 46 identical chromosomes each.
* 2 diploid cells
* Germ Cells (gametes)
* Go through meiosis
* Like mitosis, but with 2 stages of division
* Result is 4 daughter cells, each with a different set of 23 chromosomes.
* 4 haploid cells
