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Questions and Answers
What is the role of nitrogenous bases in the DNA structure?
During transcription, which nucleotide base in RNA replaces thymine from the DNA template?
What occurs at the ribosome during protein translation?
Which pair of nitrogenous bases correctly reflects base pairing in DNA?
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What feature of the DNA structure allows for complementary base pairing?
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What are the basic units of life according to cell theory?
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Which part of the cell is responsible for protein synthesis?
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Which of the following correctly describes the function of a transmission electron microscope?
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What is the main advantage of electron microscopes over compound light microscopes?
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What component is NOT common to all cells?
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What type of bond is formed when two monosaccharides are linked together?
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Which monosaccharide is involved in the formation of sucrose?
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What is the main structural characteristic of cellulose?
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What type of lipids primarily serve as building blocks for hormones?
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In starch, which type of glycosidic bond connects glucose monomers?
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Which characteristic distinguishes triglycerides from phospholipids?
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What describes the structural form of ribose when it forms a ring?
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Which of the following is a characteristic of lipids?
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What characteristic of plasma membranes contributes to the differing functions of their inner and outer surfaces?
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Which statement best describes passive transport across the plasma membrane?
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Which of the following factors does NOT affect the rate of diffusion?
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What role do glycoproteins play in the plasma membrane?
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What process allows only small non-polar molecules to pass directly through a biological membrane?
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What is the primary function of lysosomes in animal cells?
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Which component of the endoplasmic reticulum is primarily involved in protein synthesis?
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What is the primary role of the Golgi apparatus in cellular processes?
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What distinguishes the smooth endoplasmic reticulum from the rough endoplasmic reticulum?
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Which component of the cytoskeleton is primarily responsible for providing a framework for motor proteins?
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What is the primary function of plasmodesmata in plant cells?
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What is the significance of carbohydrate molecules in the plasma membrane?
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How does cholesterol affect membrane fluidity?
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Which of the following best describes the fluid mosaic model of the plasma membrane?
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What property of phospholipids allows them to form a bilayer in the plasma membrane?
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Study Notes
Monosaccharides
- Exist as linear chains or ring-shaped molecules.
- Five- and six-carbon monosaccharides exist in equilibrium between linear and ring forms.
- Ring forms are locked into alpha or beta positions.
- Fructose and ribose also form rings.
- They form five-member end rings as opposed to the six-membered ring of glucose.
Disaccharides
- Formed when two monosaccharides are linked in a dehydration reaction.
- Example: Glucose + Fructose = sucrose (disaccharide).
- Two monomers are joined by a glycosidic bond.
- Water is released.
- Carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group.
- Glycosidic linkage is formed between carbon 1 in glucose and carbon 2 in fructose.
- Results in 1,2 glycosidic linkages.
Other Common Disaccharides
- Maltose (grain sugar).
- Lactose (milk sugar).
- Sucrose (table sugar).
- All are created via the formation of covalent glycosidic linkages.
Polysaccharides
- Long chains of monosaccharides joined by glycosidic linkages.
- May be branched or unbranched.
- May consist of multiple layers of monosaccharides.
- Molecular weight could be >10,000 Daltons.
- Polysaccharides can be distinguished by their glycosidic linkages.
Starch
- Composed of Amylose and Amylopectin.
- Monomers are joined in two linkage types: α 1-4 glycosidic bonds and α 1-6 glycosidic bonds.
- Amylose = unbranched glucose monomers in α 1-4 glycosidic bonds.
- Amylopectin = branched glucose monomers in α 1-4 and α 1-6 glycosidic bonds.
Cellulose
- A polysaccharide found in the cell wall of plants.
- Glucose monomers are linked in unbranched chains by β 1-4 glycosidic linkages.
- Every glucose monomer is flipped relative to the next one, resulting in a linear, fibrous structure.
Chitin
- The hard exoskeleton of arthropods is composed of the polysaccharide chitin.
- Contains nitrogen.
Lipids
- Diverse group of non-polar hydrocarbons.
- Non-polar hydrocarbons are hydrophobic.
Function of Lipids
- Long-term energy stores.
- Provide insulation from the environment for plants and animals.
- Serve as building blocks for some hormones.
- Important components of cellular membranes.
Types of Lipids
- Fats.
- Oils.
- Waxes.
- Phospholipids.
- Steroids.
Fats and oils
- Fats – contain two main components: Glycerol and one or more phosphate groups.
- Types of Nitrogenous Bases: Pyrimidine – cytosine, thymine, uracil; Purines – adenine, guanine.
- Types of Pentose Sugars: Deoxyribose (found in DNA) and Ribose (found in RNA).
DNA Exhibits a Double Helix Structure
- The sugar and phosphate lie on the outside of the helix.
- Nitrogenous bases are stacked in the interior.
- The strands of the helix run in opposite directions (antiparallel orientation).
- Each base from one strand interacts via hydrogen bonding with a base from the opposing strand.
Base-pairing in DNA
- The two strands run antiparallel to one another.
- One strand runs 5’ to 3’.
- The other 3’ to 5’.
- Adenine forms hydrogen bonds with thymine (A-T).
- Guanine base pairs with cytosine (G-C).
The DNA Code can be Written (Transcribed) into RNA
- DNA can express a particular gene by synthesizing RNA via the process of transcription.
- RNA base sequence is complementary to the DNA sequence but in RNA, the base uracil is used in place of thymine.
- Example of transcription: if DNA sequence is AATTGCGC then mRNA complement is UUAACGCG.
RNA and the Production of Proteins
- Various forms of RNA play important roles in protein translation.
- Ribosomes are made up of proteins and rRNA – the mRNA transcript binds with ribosomes and the rRNA has catalytic activity.
- The bases of the mRNA are read in sets of three bases (codons).
- The tRNA base pairs with the codon and delivers the correct amino acid.
- Peptide linkages are made at the ribosome—polypeptide continues to grow.
Protein Translation Overview
- Ribosome has two parts: a large subunit and a small subunit.
- The mRNA sits in between the two subunits.
- A tRNA molecule recognizes a codon on the mRNA.
- Binds to it by complementary base pairing.
- Adds the correct amino acid to the growing peptide chain.
Cells
- Are the building blocks of all organisms.
- In a single-celled organism, the cell is everything.
- Size varies; most are too small to be seen by the naked eye.
- Microscopes make small cells easier to see.
Multicellular Organisms are Organized in a Hierarchy
- Cells are the basic unit.
- Tissues are composed of interconnected cells with a common function.
- Several tissues combine to form an organ.
- Organs working together make up an organ system.
- Multiple systems that function together form the entire organism.
The Two Parameters Most Important in Microscopy
- Magnification and Resolving Power.
Magnification
- The process of enlarging an object in appearance.
Resolution
- The ability of a microscope to distinguish two adjacent structures as separate.
- The higher the resolution, the better the clarity and detail of the image.
Microscopes with Different Optical Systems Produce Images for Different Studies
- Compound light microscopes bend visible light to provide magnification.
- Transparent objects (like cells) must be treated with chemical stains to distinguish different parts.
Electron Microscopes
- Achieve higher magnification and resolution using beams of electrons.
- Transmission electron microscopes can show fine detail within cells.
- Scanning electron microscopes provide 3-D exterior views.
Cell Theory
- An underlying principle of biology.
- Cells are the basic units of life.
- All living organisms are made of cells.
- All cells come from preexisting cells.
Cells have 4 Common Components
- An enclosing plasma membrane that separates the cell’s interior from the environment.
- Cytoplasm made of cytoskeleton in which other components of the cell are found.
- DNA - the genetic material of the cell.
- Ribosomes which synthesize proteins.
Characteristics of Prokaryotes
- Lack membrane-enclosed internal compartments (e.g. Lysosomes).
Lysosomes
- In animal cells, contain digestive enzymes that breakdown large biomolecules and even out organelles.
Endoplasmic Reticulum (ER)
- Interconnected membranous sacs and tubules.
- Modifies proteins (Rough ER) and synthesizes lipids (Smooth ER).
Rough Endoplasmic Reticulum
- Ribosomes attached to the cytoplasmic surface manufacture proteins.
- New proteins are modified (by folding or obtaining side chains) in the lumen of the RER.
- Makes phospholipids for cellular membranes.
- Phospholipids or modified proteins are not destined to stay in the RER, they reach their destinations via transport vesicles.
Smooth Endoplasmic Reticulum
- Is continuous and has few or no ribosomes on its surface.
Functions of SER
- Synthesis of carbohydrates, lipids, and steroid hormones.
- Detoxification of medications and poisons.
- Storage of Ca++.
Golgi Apparatus
- Lipids and proteins get sorted, packaged and tagged, while within transport vesicles, to get to the right place.
- The receiving side of the apparatus is called the CIS face; the opposite side is the TRANS face.
- Transport vesicles from the ER fuse with the CIS face and empty their contents into the lumen of the Golgi apparatus.
- As the proteins and lipids travel through the Golgi, they are further modified so they can be sorted (this involved adding short chaining of sugar molecules).
Cytoskeleton
- A network of protein fibers.
- Has several functions: helps maintain the shape of the cell, hold some organelles in specific positions, and allows movement of cytoplasm and vesicles within the cell.
Three Components of Cytoskeleton
- Microfilaments.
- Intermediate filaments.
- Microtubules.
- Each are different sizes and have different functions.
Microfilament
- Narrowest of the three types (movement and structure).
- Involved in movement (has no role in cell movement, just structure).
- Determine and stabilizes shape (movement and structure)
- Made from actin monomers.
Microtubules
- Widest component of the three.
- Provide framework for moto proteins to move structures within a cell.
- Made of tubulin dimers.
Cilia and Flagella
- Cilia is shorter and more numerous than Flagella.
Extracellular Structures
- Plant cell wall: Supports, acts as a barrier to infection, and connects cells via plasmodesmata.
- Extracellular matrix in animals (3 components): Collagens and fibrous proteins, Glycoproteins, Linking proteins.
Intercellular Junctions
- Provide direct channels of communication between cells.
- Plants and animals do this differently.
Plasmodesmata
- Channels that pass between cell walls in plants to connect cytoplasm and allow materials to move from cell to cell.
Gap Junctions Connect Animal Cells
- Form channels that allow ions, nutrients, and other materials to move between cells.
- Develop when 6 proteins form an elongated doughnut-like structure in the plasma membrane.
Plasma Membrane Functions
- Defining the outer border of all cells and organelles.
- Managing what enters and exits the cell.
- Receiving eternal signals and initiating cellular responses.
Fluid Mosaic Model
- A mosaic of components (phospholipids, cholesterol, proteins, and carbohydrates) that give the membrane a fluid character.
Phospholipids
- 2 fatty acid chains (non-polar) – hydrophobic tails.
- A glycerol molecule, a phosphate group (polar) - hydrophilic head.
- Each fatty acid can either be saturated or unsaturated:
- Carbons are saturated (maximum amount of hydrogen) with H- all single C-C bonds.
- Unsaturated is when at least one double C=C bond occurs.
Phospholipid Bilayer
- Arrange themselves in a bilayer.
- Polar head face outward.
- Hydrophobic tails face inward.
Proteins
- The second major component of membrane.
- Functions as transporters, receptors, enzymes, or in binding and adhesion.
- Integral proteins – integrated completely into the bilayer.
- Peripheral proteins – occur only on the surfaces.
Integral Proteins
- Has one or more regions that are hydrophobic and others that are hydrophilic.
- The location and number of regions determine how they arrange within the bilayer.
Carbohydrates
- Located on the exterior surface of the plasma membrane, bound to either proteins (forming glycoproteins (sugar + protein)) or to lipids (forming glycolipids (sugar + lipid)).
Receptor Proteins
- Our immune systems T cells have CD4 receptor glycoproteins that recognize HIV as “self”.
Membrane Fluidity
- The membrane needs to be flexible but not so fluid that it cannot maintain its structure.
- Fluidity is affected by:
- Phospholipid type - phospholipids with saturated fatty acids can pack together more closely than theses with unsaturated fatty acids (therefore, more SFA, more rigid, less fluidity).
- Temperature - cold temperatures compress molecules making membranes more rigid.
- Cholesterol - acts as a fluidity buffer, keeping membranes fluid when cold and from not getting too fluid when hot.
Plasma Membranes
- Are asymmetric.
- The inner surface differs from the outer surface.
- For example:
- 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 (allows 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 either:
- Passive - requiring no energy.
- Active - requiring energy (ATP).
Passive Transport
- The simplest type of passive transport 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 gradients - greater difference, faster diffusion.
- Mass of the molecules - smaller molecules diffuse more quickly.
- Temperature - molecules move faster (more fluid) when temperatures are higher.
- Solvent density - dehydration increases density of cytoplasm which reduces diffusion rates.
- Solubility - more non-polar (lipid-soluble) materials, diffuse faster.
- Surface area - increase surface area speeds up diffusion rates.
- Distance traveled - the greater the distance, the slower the rates; important factor of affecting 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. …
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Description
This quiz covers the structure and formation of carbohydrates, focusing on monosaccharides, disaccharides, and polysaccharides. Learn about the ring forms of sugars, glycosidic linkages, and examples of common disaccharides such as sucrose and lactose. Test your understanding of these essential biological molecules!
