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Questions and Answers
What defines the primary structure of a protein?
How does sickle cell anemia illustrate the importance of amino acid sequence?
Which level of protein structure involves local folding due to hydrogen bonding?
What is the potential consequence of altering the order of amino acids in a protein?
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What can result from a change in the nucleotide sequence of DNA?
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What characteristic distinguishes the inner surface of the plasma membrane from the outer surface?
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Which type of transport across the plasma membrane requires energy input?
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What factor would most likely increase the rate of diffusion of a substance across the plasma membrane?
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Which type of molecules can diffuse directly through biological membranes?
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What effect does an increase in solvent density have on diffusion rates?
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What is the maximum number of different atoms that carbon can form covalent bonds with?
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Which of the following best describes the geometry of methane?
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What happens to the energy stored in covalent bonds of hydrocarbons when they are burned?
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Which of the following statements is true about double bonds in hydrocarbons?
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Which of the following is NOT one of the four major classes of macromolecules?
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What is the primary structural component of prokaryotic cell walls?
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Which of the following best characterizes eukaryotic ribosomes compared to prokaryotic ribosomes?
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What is the role of the nucleolus within the nucleus?
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How do plant cell walls differ from prokaryotic cell walls?
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What distinguishes centrosomes in animal cells from those in plant cells?
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What are cristae and where are they found?
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Which statement best describes the endomembrane system in eukaryotic cells?
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What is the primary function of the central vacuole in plant cells?
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What is the main purpose of the nuclear pores in the nuclear envelope?
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Why are prokaryotic cells typically smaller than eukaryotic cells?
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What is the primary role of channel proteins in facilitated diffusion?
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What characterizes a hypotonic solution?
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Which type of active transport directly uses ATP as its energy source?
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How do carrier proteins function in facilitated transport?
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Which of the following statements is true regarding osmosis?
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What distinguishes phagocytosis from pinocytosis?
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Which type of pump is characterized by transporting two different molecules or ions in the same direction?
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What is the primary reason energy is required for active transport?
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What occurs during exocytosis?
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Study Notes
Carbon
- Key component of macromolecules
- Forms covalent bonds with up to four different atoms
- Serves as a "backbone" for the macromolecules
- Has four electrons in the outer shell
- Forms four covalent bonds to fill the outer shell, allowing it to achieve the "octet rule"
Hydrocarbons
- Carbon + Hydrogen (Ex: Methane)
- Covalent bonds between atoms store energy, which is released when the molecules are burned
- The energy released from hydrocarbons is used to heat homes and power cars
Methane
- Binds to four hydrogens to satisfy the octet rule
- Has a tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart
Hydrocarbon Chains
- Carbon forms single bonds with other atoms, resulting in a tetrahedral shape.
- Two carbon atoms form a double bond, resulting in a planar (flat) shape.
- Single bonds can rotate, while double bonds cannot.
Hydrocarbon Rings
- Carbon can form five and six-membered rings (closed chain)
- Single or double bonds connect the carbons in the ring
- Nitrogen can substitute for carbon
- Benzene is an important hydrocarbon ring used in various molecules, including amino acids, cholesterol, and its derivatives.
Four Major Classes of Macromolecules:
- Carbohydrates
- Lipids
- Proteins
- Polypeptides - a chain of amino acids joined together in peptide linkages
- Proteins - a polypeptide or multiple polypeptides
- Often combined with non-peptide prosthetic groups
- Have unique structures and functions
- Many proteins are modified following translation (the process of creating a new protein)
Protein Structure
- The shape of a protein is crucial for its function
- Protein shape is determined by four levels of structure:
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
Primary Protein Structure
- The unique sequence of amino acids in a polypeptide
- Protein function can be compromised if the order of amino acids is altered
- The amino acid sequence is based on the gene encoding the protein
- A change in the nucleotide sequence of DNA can lead to a change in the amino acid sequence, potentially affecting protein structure and function
Sickle Cell Anemia
- An example of how a change in one amino acid can impact human health
- Normal hemoglobin has glutamic acid at position seven
- Sickle cell hemoglobin replaces glutamic acid with valine
- This single amino acid change in the 600 amino acids that code for human hemoglobin alters the shape of red blood cells from disc-shaped to crescent shaped.
Secondary Protein Structure
- Local folding of the polypeptide
- α-helix – formed by hydrogen bonding between oxygen in the carbonyl group and an amino acid four positions down the chain
- β- pleated sheet – formed by hydrogen bonding between atoms in the polypeptide backbone (not the side chains)
Tertiary Protein Structure
- The three-dimensional structure of a single polypeptide chain
- Interactions between R-groups (side chains) of amino acids contribute to the tertiary structure, including:
- Hydrophobic interactions
- Hydrogen bonds
- Ionic bonds
- Disulfide bridges
Quaternary Protein Structure
- The arrangement of multiple polypeptide chains (subunits) into a functional protein
- Held together by non-covalent interactions
Prokaryotes
- Primarily unicellular organisms
- Lack internal membrane-bound organelles (nucleus, mitochondria, etc.)
- Most have a cell wall containing peptidoglycan
- Believed to be much like the first cells
- Organisms in the domains Archaea and Bacteria are Prokaryotes
Generalized Structure of a Prokaryotic Cell
- Chromosomal DNA is localized in a nucleoid
- Ribosomes are in the cytoplasm
- The cell membrane is surrounded by a cell wall
Prokaryotic Cells are Smaller than Eukaryotic Cells
- The surface area to volume ratio is more favorable for moving material in and out of the cell
- They lack modifications found in eukaryotes that aid internal transport
Factors Limiting Cell Size
- Surface area-to-volume ratio
- As cells get bigger, volume increases faster than surface area
Eukaryotic Plasma Membrane
- Phospholipid bilayer with embedded proteins
- Provides a selectively permeable barrier, regulating what enters and leaves the cell.
Cytoplasm
- Region between the plasma membrane and the nuclear envelope
- Contains organelles suspended in a gel-like cytoskeleton plus the cytoskeleton itself
- Composed of 70-80% water, but its semi-solid consistency is due to the proteins within it.
Nucleus
- Usually only one per cell
- Usually the largest organelle
- Larger than most prokaryotic cells
Nuclear Envelope
- A double membrane that separates DNA from the cytoplasm and separates transcription from translation
- Nuclear pores perforate this membrane, connecting the nucleoplasm to the cytoplasm
- These pores regulate the flow of molecules back and forth; large molecules require a nuclear localization signal (NLS) to pass.
Nucleolus
- A region inside the nucleus where ribosomes are assembled from RNA and proteins
Ribosomes
- Made of two different-sized subunits; slightly larger in eukaryotes
- Composed of special RNA (rRNA) and proteins
- During protein synthesis, ribosomes assemble amino acids into proteins
Mitochondrion
- Site for conversion of stored energy (macromolecule molecular bonds) to a more useful form (ATP)
- Inner membrane is folded, with folds called cristae
- The area enclosed is the mitochondrial matrix
Peroxisomes
- Reactions that break down fatty acids and amino acids occur here.
- May detoxify poisons
Contrasting Animal and Plant Cells
- Both have microtubule organizing centers (MTOCs), but animal cells have centrioles associated with the MTOC; this complex is called the centrosome
- Animal cells have lysosomes, plant cells do not
- Plant cells have a cell wall, chloroplasts, other specialized plastids, and a large central vacuole; animal cells do not
Animal Cells Include:
- Intermediate filament
- Ribosomes
- Rough endoplasmic reticulum
- Nucleus
- Nucleolus
- Chromatin
- Golgi apparatus
- Golgi vesicle
- Cytoplasm
- Vacuole
- Peroxisome
- Secretory vesicle
- Smooth endoplasmic reticulum
- Lysosomes
- Microfilament
- Centrosomes
- Microtubule
- Plasma membrane
- Mitochondria
Plant Cells Include:
- Plasmodesmata
- Cell wall
- Plasma membrane
- Cytoplasm
- Central vacuole
- Cytoskeleton
- Chloroplast
- Plastid
- Peroxisome
- Golgi apparatus
- Mitochondria
- Ribosomes
- Nucleus
- Rough and smooth endoplasmic reticulum
Centrosome
- Consists of two centrioles that lie at right angles to each other
- Each centriole is a cylinder made up of nine triplets of microtubules
- Nontubulin proteins hold the microtubule triplets together
Plant Cell Walls
- A rigid protective structure external to the plasma membrane
- Differ from prokaryotes as they are made up of cellulose rather than peptidoglycan
Chloroplasts
- Double-membrane organelles; have their own ribosomes and DNA, similar to mitochondria
- The inner membrane encloses an aqueous fluid (stroma), which contains a set of interconnected and stacked fluid-filled membrane sacs called thylakoids. Each stack of thylakoids is a granum (plural = grana).
The Central Vacuole
- Plant cells have a large vacuole that occupies most of the area of the cell
- Helps regulate water concentration under changing environmental conditions and contributes to cell expansion
The Endomembrane System
- Consists of internal membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins
- Includes:
- Nuclear envelope
- Lysosomes
- Vesicles
- Endoplasmic reticulum
- Golgi apparatus
- The plasma membrane
Plasma Membranes
- Asymmetric
- Inner surface differs from outer surface
- Interior proteins anchor fibers of the cytoskeleton to the membrane
- Exterior proteins bind to the extracellular matrix (outside of the cell)
- Glycoproteins bind to substances the cell needs to import
Transport
- The plasma membrane is selectively permeable, allowing some molecules to pass through, but not others
- This allows cytosol solutions (inside the cell) to differ from extracellular fluids
- Transport across a membrane can be passive (requiring no energy) or active (requiring energy (ATP))
Passive Transport
- The simplest type is diffusion
- Diffusion: occurs when a substance from an area of high concentration moves down its concentration gradient
- Only small non-polar molecules (O2, CO2, lipid hormones) can diffuse through biological membranes
Factors That Affect Diffusion Rates
- Concentration gradient - greater difference, faster diffusion
- Mass of the molecules - smaller molecules diffuse more quickly
- Temperature - molecules move faster (more fluid) at higher temperatures
- Solvent Density - dehydration increases the density of the cytoplasm, which reduces diffusion rates
- Solubility - more non-polar (lipid-soluble) materials diffuse faster
- Surface area - increase in surface area speeds up diffusion rates
- Distance traveled - the greater the distance, the slower the rate; important factor affecting the upper limit of cell size
- Pressure - in some cells (i.e., kidney cells), blood pressure forces solutions through membranes, speeding up diffusion rates
Facilitated Passive Transport
- Facilitated transport (a.k.a. facilitated diffusion) moves substances down their concentration gradient through transmembrane integral membrane proteins
- Two types of facilitated transport proteins:
- Channel proteins
- Carrier proteins
Channel Proteins
- The top, bottom, and inner core are composed of hydrophilic amino acids, attracting ions &/or polar molecules
- Some are always open
- Others are gated, only opening when a signal is received
- Important examples:
- Aquaporins - specific to H2O
- Muscle cells have gated ion channels that allow muscle contraction when opened.
Carrier Proteins
- Specific to a single substance
- They bind to that substance, change shape, and “carry it” to the other side
- Many allow movement in either direction, as concentration gradients change
Osmosis
- The diffusion of water across the membrane
- Water always moves from an area of higher water concentration to a lower water concentration
- Differences in water concentration occur when a solute cannot pass through the selectively permeable membrane
Osmolarity
- Describes the total solute concentration (salt, sugar, etc.)
- Low osmolarity - less solute, more water
- Hypotonic: extracellular fluid has lower osmolarity (less solute, more water outside the cell) than the cytosol - water enters the cell
- Isotonic: extracellular fluid has the same osmolarity (equal solute and water inside and outside of the cell) than the cytosol - water does not move
- Hypertonic: extracellular fluid has higher osmolarity (high solute, less water outside the cell) than the cytosol - water leaves the cell
Active Transport
- Used anytime an ion or molecule (like glucose) is transported through a membrane protein
- Against its concentration gradient (from low to high concentration) or against its electrochemical gradient
- Energy is always required for active transport
- Two types of active transport:
- Primary - where ATP provides the energy
- Secondary - where an electrochemical gradient provides the energy
- Occurs through transmembrane, integral carrier proteins called pumps
- There are 3 types of pumps:
- Uniporter: carries one molecule or ion
- Symporter: carries two different molecules or ions in the same direction
- Antiporter: carries two different molecules or ions in different directions
Electrochemical Gradient
- Arise from the combined effects of concentration gradients and electrical gradients
Primary Active Transport
- Moves an ion or molecule up its concentration gradient, using energy from ATP hydrolysis
Secondary Active Transport
- Uses an electrochemical gradient, created by primary active transport to move a different substance against its concentration gradient
Bulk Transport
- Used when cells need to import or export molecules/particles that are too large to pass through a transport protein
- A type of active transport requiring energy
- Importing by bulk transport is called endocytosis (into the cell); exporting is called exocytosis (outside of the cell)
- Two types of endocytosis:
- Phagocytosis - (cellular eating), the cell membrane surrounds a particle and engulfs it
- Pinocytosis - (cellular drinking), the cell membrane invaginates, surrounds a small volume of fluid, and pinches off
Exocytosis
- Vesicles containing substances fuse with the plasma membrane
- The contents are then released to the exterior of the cell
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Description
Explore the fascinating world of carbon and hydrocarbons through this quiz. Learn about the properties of carbon, the structure of hydrocarbons, and the significance of covalent bonds. Test your understanding of hydrocarbon chains and rings as well.
