Podcast
Questions and Answers
Which type of tissue is responsible for binding and supporting other tissues?
Which type of tissue is responsible for binding and supporting other tissues?
What is the function of dendrites in a neuron?
What is the function of dendrites in a neuron?
Transmit impulses from tips to the rest of the neuron
Muscle tissue is responsible for involuntary activities.
Muscle tissue is responsible for involuntary activities.
False
What is the function of the cell membrane?
What is the function of the cell membrane?
Signup and view all the answers
What are the functions of membrane proteins?
What are the functions of membrane proteins?
Signup and view all the answers
Transmembrane proteins have both hydrophobic and hydrophilic regions.
Transmembrane proteins have both hydrophobic and hydrophilic regions.
Signup and view all the answers
______ contains almost all of the cell's hereditary information.
______ contains almost all of the cell's hereditary information.
Signup and view all the answers
Match the organelles with their descriptions:
Match the organelles with their descriptions:
Signup and view all the answers
What is the characteristic of the β-pleated sheet in terms of its chain arrangement?
What is the characteristic of the β-pleated sheet in terms of its chain arrangement?
Signup and view all the answers
What is the primary driving force behind the folding of soluble proteins into globular structures?
What is the primary driving force behind the folding of soluble proteins into globular structures?
Signup and view all the answers
What is the characteristic of the α-helix in terms of its handedness?
What is the characteristic of the α-helix in terms of its handedness?
Signup and view all the answers
What is the role of hydrogen bonding in the formation of the β-pleated sheet?
What is the role of hydrogen bonding in the formation of the β-pleated sheet?
Signup and view all the answers
What is the result of the tightest turn a polypeptide chain can make in a β-turn?
What is the result of the tightest turn a polypeptide chain can make in a β-turn?
Signup and view all the answers
What is the primary driving force behind the formation of tertiary structure in proteins?
What is the primary driving force behind the formation of tertiary structure in proteins?
Signup and view all the answers
What is the consequence of the flexibility of the polypeptide chain at points of instability?
What is the consequence of the flexibility of the polypeptide chain at points of instability?
Signup and view all the answers
What is the characteristic of the parallel β-pleated sheet?
What is the characteristic of the parallel β-pleated sheet?
Signup and view all the answers
What is the result of the formation of other noncovalent bonds between side-chain groups?
What is the result of the formation of other noncovalent bonds between side-chain groups?
Signup and view all the answers
What is the characteristic of the β-pleated sheet in terms of its H bond formation?
What is the characteristic of the β-pleated sheet in terms of its H bond formation?
Signup and view all the answers
Study Notes
Cell Structure and Functions
- Cell membrane: dynamic, fluid structure that encloses the cell and maintains differences between the cytosol and extracellular environment.
- Membrane structure: thin film of lipid and protein molecules held together by non-covalent interactions.
- Lipid molecules: arranged in a continuous double layer, about 5 nm thick, providing the basic fluid structure and impermeable barrier to water-soluble molecules.
- Lipid molecules constitute about 50% of the mass of animal cells, with approximately 10^9 lipid molecules in the plasma membrane of a small animal cell.
Membrane Proteins
- Perform most of the membrane's specific tasks, giving each type of cell membrane its characteristic functional properties.
- Amounts and types of membrane proteins vary highly, with some membranes having less than 25% protein (e.g., myelin membrane) and others having approximately 75% protein (e.g., internal membranes of mitochondria and chloroplast).
- There are always more lipid molecules than protein molecules in the cell membrane, with about 50 lipid molecules for each protein molecule.
Membrane Protein Functions
- Transport
- Enzymatic activity
- Signal transduction
- Intercellular joining
- Cell-cell recognition
- ECM attachment
Transmembrane Proteins
- Amphiphilic, with hydrophobic regions passing through the membrane and interacting with the hydrophobic tails of lipid molecules, and hydrophilic regions exposed to water on either side of the membrane.
- Covalent attachment of a fatty acid chain increases the hydrophobicity of some transmembrane proteins.
Peripheral Membrane Proteins
- Do not extend into the hydrophobic interior of the lipid bilayer.
- Bound to either face of the membrane by non-covalent interactions with other membrane proteins.
- Can be released from the membrane by gentle extraction procedures, exposure to solutions of very low or high ionic strength, or extreme pH.
Nucleus
- Spherical or oval structure containing almost all of the cell's hereditary information.
- Nuclear envelope: double membrane structure that surrounds the nucleus.
- Nuclear pores: control the movement of substances between the nucleus and cytoplasm.
- Nucleoli: spherical bodies where rRNA is synthesized.
DNA Packaging
- Nuclear DNA contains histones.
- Nucleosomes: 165 bp of DNA + 8 molecules of histones.
- Chromatin: threadlike appearance of DNA when not reproducing.
- Chromosomes: chromatin becomes short, thick bodies during cell division.
Endoplasmic Reticulum
- Extensive network of flattened membranous sacs or tubules called cisterns.
- Continuous with the nuclear envelope.
- Rough ER: studded with ribosomes.
- Smooth ER: no ribosomes on its surface, synthesizes phospholipids, fats, and steroids.
Ribosomes
- Sites of protein synthesis.
- Proteins synthesized to attached ribosomes enter cisterns within the ER for processing and sorting.
- In some cases, enzymes attach the proteins to carbohydrates to form glycoproteins or to phospholipids.
Golgi Complex
- An organelle consisting of 3-20 cisterns.
- Proteins synthesized by attached ribosomes are initially transported in this organelle.
- Proteins are modified and move from one cistern to another via transfer vesicles that bud from the cistern's edges.
- Enzymes in the cisterns modify the proteins to form glycoproteins, glycolipids, and lipoproteins.
Lysosomes
- Formed from Golgi complexes that look like membrane-enclosed spheres.
- Single-membraned and lack internal structure.
- Contain 40 kinds of digestive enzymes that break down various molecules, including bacteria.
- Abundant in human WBC.
Vacuoles
- Space or cavity in the cytoplasm that is enclosed by a membrane called the tonoplast.
- In plant cells, vacuoles occupy 5-90% of the cell volume, depending on the type of cell.
- Some serve as storage of proteins, sugars, organic acids, and inorganic ions; also, metabolic poisons and wastes (in plants).
- Help bring food to the cell.
- May take up water, enabling plant cells to increase in size and provide rigidity to leaves and stems.
Mitochondria
- Spherical or rod-shaped, appearing throughout the cytoplasm.
- Double-membrane: outer smooth, inner series of folds (cristae).
- Center part: matrix.
- No. in the cell varies, with liver having 1000-2000 mitochondria.
- Contains 70s ribosomes and some DNA of their own, as well as the machinery needed to replicate, transcribe, and translate the information encoded by their DNA.
Chloroplasts
- Found in green algae and plants.
- Membrane-enclosed structure containing pigment chlorophyll and enzymes required for photosynthesis.
- Thylakoids: flattened membrane sacs that contain chlorophyll.
- Grana: stacks of thylakoids.
Peroxisomes
- Single-membrane-bound organelles.
- Contain one or more enzymes that use molecular oxygen to remove hydrogen atoms from specific organic substrates.
- Do not contain DNA or ribosomes.
- Usually contain 50 different enzymes involved in different biochemical pathways.
Centrosome
- Located near the nucleus.
- Two components: pericentriolar area and centriole.
- Pericentriolar material: region of the cytosol composed of a dense network of small protein fibers; organizing center for the mitotic spindle; microtubule formation in nondividing cells.
- Centrioles: composed of nine clusters of three microtubules (triplets) arranged in a circular pattern.
Cellular Compartmentalization
- Advantages of compartmentalization:
- Allows the cell to carry out different metabolic activities due to the established physical boundaries.
- Generate a specific micro-environment to spatially or temporally regulate a biological process.
- Establish specific locations or cellular addresses for which processes should occur.
Tissues
- Groups of cells with a common structure and function.
- Four types:
- Epithelial: outside of the body and lines organs and cavities.
- Connective: binds and supports other tissues.
- Nervous: senses stimuli and transmits signals.
- Muscle: capable of contracting when stimulated by nerve impulses.
Peptide Bond Formation
- Peptide bond formation is a highly endergonic process, requiring the hydrolysis of high-energy phosphate bonds.
- Water is removed during the process, resulting in a bond between the α-carboxyl group of one amino acid and the α-amino group of another.
Characteristics of the Peptide Bond
- The peptide bond is planar, with adjacent α-carbons, carbonyl oxygen, α-amino nitrogen, and associated hydrogen atoms lying in the same plane.
- The peptide bond has a partial double-bond character due to resonance, preventing rotation around the bond axis.
- Peptide bonds are resistant to denaturation by heat or high concentrations of urea, but can be hydrolyzed by strong acid or base at elevated temperatures.
Conformation of Proteins
- A protein in its native state has a unique three-dimensional structure (conformation).
- Primary structure refers to the linear sequence of amino acids joined by peptide bonds, forming a covalent "backbone" of the polypeptide.
- The amino acid sequence is coded for by DNA and determines the final three-dimensional form of the protein.
Amino Acid Characteristics
- Basic amino acids have side chains with net positive charges at neutral pH, including histidine, arginine, and lysine.
- Proline is an imino acid with an aliphatic side chain, bonded to both the nitrogen and α-carbon atoms, and is more conformationally restricted due to its ring structure.
Post-Translational Modifications
- More than 100 different kinds of amino acids can be formed through post-translational modifications, including:
- Hydroxylation of prolines and lysines in collagen
- Methylation of lysines and histidines in muscle myosin
- Carboxylation of glutamates in blood clotting and bone proteins
- Phosphorylation of serine, threonine, and tyrosine molecules
Peptides and Polypeptides
- Peptide chains refer to the linking of amino acids.
- Polypeptides are composed of many amino acids linked together.
- Amino acids in polypeptide chains are referred to as residues.
Secondary Structure
- α-helices have 3.6 amino acid residues per turn, with a right-handed (clockwise) orientation.
- β-pleated sheets form through hydrogen bonds between peptide bonds in different chains.
- β-pleated sheets can be parallel or antiparallel, depending on the direction of the chains.
Tertiary Structure
- Tertiary structure refers to the spatial relations of more distant residues.
- Folding of polypeptide chains occurs due to associations between secondary structures, resulting in a state of lowest energy (greatest stability) for the protein.
- Hydrophobic side chains are located in the interior of the structure, while hydrophilic side chains are on the outside, in contact with water.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Learn about the dynamic structure of cell membranes, their composition, and functions in maintaining cellular environments.
