Chapter 2 Molecules And Cells Flashcards
What is this model? What is composed of?
Fluid mosaic model.
Lipid, proteins, and carbohydrates.
Phospholipid characteristics
Amphipathic: hydrophobic and hydrophilic
Polar head
Non-polar tail
- Saturated if fatty acid tails do not have any double bonds
- Unsaturated if double bonds are present
Phospholipid Characteristics 2
Phospholipids become more rigid when cold
Fish living in polar environments incorporate moreunsaturated fatty acids to prevent stiffness
unsaturated-double bond
saturated- no double bond
Cholesterol
Reduces the effect of temperature variations on membrane fluidity
Increases membrane fluidity by preventing phospholipids from being tightly packed
Provides rigidity at high temperatures
increases fluidity when cold and decreases it when warm
Types of membrane proteins and functions
Intergral and peripheral
channels, transporters (carriers), enzymes, receptors, and structural proteins.
Levels of protein structure
Primary - linear sequence of AA composing the polypeptide chain
Secondary- twist or bend upon themselves to form a more complex structure: alpha helix or beta pleated sheets (hydrogen bonds)
Tertiary-3d shape of polypeptide chain; unique for each protein (combo beta and alpha)
Quarternary- (hemoglobin)
Denaturation
the unfolding of proteins by hostile in enivorments
temp, pH,
Carbohydrates
Carbohydrates are covalently bound to proteins and lipids
Types
Glycoprotein
Glycolipids
Proteoglycans
Always on the outside of the cell and may serve as attachment sites for extracellular proteins and as cell-recognition sites
Epithelia
Forms a boundary by covering a body or organ surface or lining a cavity
Characteristics:
Cellularity
Polarity
Ennervated
Avascular
Regenerative
Supported by connective tissue
Epithelia
Junctions
Tight Junctions- hold cells together and prevents substances from passing between cells
Septate Junctions- found in invertebrates
Desmosomes- hold cells together and found in tissues that stretch
- Skin
- Heart
Junctions 2: gap junctions
Composed of connexons
- Made up of connexins
Allows passage of small molecules from one cell to another
Electrical synapse (communicates with electricty)
6 protein subunits is a hemichannel
ions move through
Intercellular transport
Paracellular and Transcellular
Metabolism
All of the chemical reactions occurring within the animal
Main types
Catabolic- breaks down complex to simple
Anabolic- builds simple to complex
Metabolic rate: The speed of these reactions
Reactant concentration, temperature, particle size influence speed
speed can be increased by using enzymes
What are enzymes?
Catalysts that speed up reactions without being modified
- Can be used to regulate the speed of chemical reactions
- Reactions can go in both directions (Law of Mass Action) (tells which way a rxn goes)
Bind with, and act upon substrates to produce products
Enzymes Characteristics
Have 3D shapes
- Substrates (ligands) bind at the active site
- Weak, non-covalent bonds
- May have more than one active site
- Binding is specific due to chemical and electrochemical properties
- Binding changes the shape of the enzyme
- Cooperativity
- Positive vs. negative
- Homotropic vs. heterotropic
Allosteric regulation: Non-substrate binding alters catalytic rate
Enzyme kinetics
Enzymes display saturation kinetics
Maximum velocity determined by:
- Enzyme quantity
- Enzyme effectiveness
Hyperbolic (Michaelis-Menton)
- Enzyme usually has 1 binding site
Sigmoid
- Enzyme has multiple binding sites
Enzyme kinetics continued
Affinity
Probability that an enzyme and substrate interact to form a complex
- At normal substrate concentrations, high affinity enzymes produce a faster reaction velocity
Apparent Michaelis Constant (Km)
- Substrate concentration needed to attain 50% of Vmax
Enzymatic regulation of cell function
Two Methods
- The types and amounts of enzymes within a cell determine which metabolic pathways are functional
- Constitutive vs. inducible enzymes
- Controlled by gene expression and degradation
- Promoters, enhancers, and transcription factors
- The activity of the enzymes may be altered to control the rate of the metabolic pathways
- Allosteric and covalent modulation
- Upregulation/downregulation
- Feedback inhibition
- Rate-limiting and branch-point enzymes are strategically important
Isozymes
Isozymes:Different forms of an enzyme within a species
Interspecific enzyme homologs: Different forms of an enzyme encoded by homologous genes in different species
Multiple forms of an enzyme occur at all levels of organization
Several types of one enzyme catalyze the same reaction
- Amino acid sequences differ
- Many forms have evolved due to genetic mutations
- May have different regulatory and catalytic properties
Protein Maintenance
Many stresses can denature proteins such as enzymes, making them nonfunctional
- Temperature
- Low cellular levels of O2
- Toxic chemicals
Molecular chaperones can correct reversible denaturation
- Also active when proteins first made
- Heat shock proteins are best known examples
Protein Maintainance Continued
The ubiquitin-proteasome system
Destroys unnecessary proteins
- E1 activates ubiquitin
- E2 attaches ubiquitin to a lysine within the target protein (polyubiquination may occur)
- The tagged protein is chopped into smaller proteins by a proteosome
- Peptidases break down the smaller proteins into amino acids
Protein Synthesis
Transcription- synthesis of mRNA from DNA
Regulated by DNA promoters and transcription factors
Translation- protein made from mRNA template
Occurs on free ribosomes
- Protein goes to nucleus, mitochondrion, or cytoplasm
Occurs on rough endoplasmic reticulum
- Protein is destined for lysosome, secretion, or plasma membrane
Regulation
- Translation can be globally regulated
- Specific regulation by mRNA 5’- and 3’- UTR sequences
