Biological Membranes and Phospholipids Quiz

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Questions and Answers

How does an increase in carbon number influence the melting temperature of phospholipids?

Increases the melting temperature (correct)

Has no effect on melting temperature

Initially increases and then decreases melting temperature

Decreases the melting temperature

What type of organized structure is formed by phospholipids in aqueous environments?

Monolayers

Micelles

Liposomes only

Bilayers (correct)

Which of the following statements is true about the Danielli-Davison Model?

It has been proven to be incorrect. (correct)

It remains a widely accepted model in modern biology.

It accurately describes the structure of biological membranes.

It was later determined to be energetically favorable.

What is the primary structural motif found in all biological membranes?

Lipid bilayer Signup and view all the answers

What type of methods includes immunofluorescence for studying biological membranes?

Biochemical/Cell biological methods Signup and view all the answers

What is the primary function of the cytoskeleton within a cell?

Structural support and movement of materials Signup and view all the answers

Which statement accurately describes ribonucleoprotein (RNP) granules?

They consist of RNA and proteins and lack a membrane. Signup and view all the answers

What has led to lipid droplets being classified as organelles?

Recognition of their functional roles. Signup and view all the answers

What does a higher protein: lipid ratio in cell membranes indicate?

Higher biological activity Signup and view all the answers

Which class of lipids serves as the 'backbone' in glycerophospholipids?

Glycerol Signup and view all the answers

What is the composition of glycoproteins in cell membranes?

More than 90% Signup and view all the answers

Which feature distinguishes prokaryotic cells from eukaryotic cells?

Organization of internal organelles Signup and view all the answers

Which cellular structure is primarily responsible for ATP and sugar production via photosynthesis?

Chloroplasts Signup and view all the answers

What is the primary function of the cell membrane?

Signal transduction Signup and view all the answers

Which organelle is primarily responsible for protein synthesis?

Ribosomes Signup and view all the answers

In which form do small, soluble aggregates develop before becoming large insoluble protein aggregates?

Oligomeric aggregates Signup and view all the answers

How does membrane compartmentalization enhance cellular function?

By segregating conflicting biochemical processes Signup and view all the answers

What role does the Golgi apparatus play in a cell?

Protein processing and modification Signup and view all the answers

Which of the following is NOT a function of the cell membrane?

Energy production Signup and view all the answers

What is a characteristic of lysosomes within the cell?

Digestion and recycling of cellular waste Signup and view all the answers

What is the main function of the smooth endoplasmic reticulum (SER)?

Synthesis of lipids Signup and view all the answers

What type of bond forms ceramide from sphingosine and fatty acids?

Amide bond Signup and view all the answers

Which statement about sphingomyelin is correct?

It is the only sphingolipid that is a phospholipid. Signup and view all the answers

What characterizes cholesterol in its structure?

It has a polar, 3-beta-hydroxyl group. Signup and view all the answers

How do phospholipids arrange themselves when mixed with water?

They form bilayers. Signup and view all the answers

What is the primary reason for the formation of organized lipid structures?

To maximize polar-nonpolar interactions. Signup and view all the answers

What discovery did Overton make regarding membrane permeability?

Non-polar substances pass through membranes quicker than polar substances. Signup and view all the answers

What was a key criticism of the Danielli-Davson model of membrane structure?

It was energetically unfavorable and inaccurate regarding protein arrangement. Signup and view all the answers

What does the 'Unit Membrane' Hypothesis propose about cellular membranes?

They possess a trilaminar structure. Signup and view all the answers

What role do PAR proteins predominantly play in cells?

They are responsible for the polarization of proteins and organelles. Signup and view all the answers

How do MTs (microtubules) contribute to cell polarity?

They are uniformly polarized with their (-) ends facing the apical side. Signup and view all the answers

What happens to mislocalized PKC during transport?

It is phosphorylated and released into the apical domain. Signup and view all the answers

What is the primary function of Rab proteins in polarized trafficking?

To determine the target membrane for proteins. Signup and view all the answers

Which protein assists in linking the spectrin network in a cell?

Ankyrin Signup and view all the answers

What is the outcome if mislocated proteins cannot relocalize?

They undergo degradation by lysosomes. Signup and view all the answers

Which components make up the Par-complex in cells?

PAR3, PAR6, aPKC Signup and view all the answers

What role does JAM play in cell polarity?

It helps anchor Par3 to the membrane. Signup and view all the answers

How does Rho-GTPase contribute to cell polarity?

By activating adhesion and relocalizing PAR proteins. Signup and view all the answers

What dual mechanism exists for sorting proteins in polarized epithelial cells?

Direct and indirect transport methods. Signup and view all the answers

Which enzyme is responsible for separating DNA strands during replication?

Helicase Signup and view all the answers

How does topoisomerase relieve torsional strain during DNA replication?

By creating breaks in the DNA strands Signup and view all the answers

In which phase of the cell cycle does DNA replication occur?

S phase Signup and view all the answers

What role does RPA play during DNA replication?

It protects single-stranded DNA from degradation Signup and view all the answers

What triggers the activation of DNA damage checkpoints?

Accumulation of ssDNA Signup and view all the answers

Which protein is responsible for binding and inactivating E2F in the cell cycle?

Rb Signup and view all the answers

Which protein complex does Atm interact with upon encountering DNA breaks?

MRN Signup and view all the answers

What is the role of p21 in the cell cycle?

It is a CDK inhibitor that arrests cell cycle progression Signup and view all the answers

How is p53 activated in response to DNA damage?

By phosphorylation, releasing it from Mdm2 Signup and view all the answers

Which mechanism allows for coordinated regulation of cell cycle events?

Dependent pathway (domino theory) Signup and view all the answers

What occurs during telophase of mitosis?

Nuclear envelopes reform around separated chromosomes Signup and view all the answers

In the context of cell cycle control, what is the role of Ras?

It phosphorylates MAPK and promotes cell growth Signup and view all the answers

What is the outcome of hydroxyurea treatment in the cell cycle?

Depletes dNTP pools, halting DNA synthesis Signup and view all the answers

Which statement about prokaryotic cell cycles is correct?

They use a histone-kinase two-component system for progression Signup and view all the answers

Study Notes

Prokaryotic vs. Eukaryotic Cells

Prokaryotic cells lack internal organelles, while eukaryotic cells do have them.
Cell walls are present in prokaryotic cells, but not in eukaryotic cells.
Flagella are present in prokaryotic cells, absent in eukaryotic cells.

Organelle Functions

Organelles are specialized structures in cells with specific functions.
Cell membranes separate intracellular and extracellular environments.
Membranes act as selective permeability barriers.
Membranes regulate biochemical processes in different cell compartments.

Membrane Compartmentalization

Increases the efficiency of biochemical reactions in the cell by increasing local substrate concentration.
Segregates anabolic and catabolic reactions into different compartments
Examples include fatty acid synthesis (in cytosol) and fatty acid oxidation (in mitochondria).

Conventional Cellular Compartments

Nucleus: Houses genetic information.
Ribosomes: Protein synthesis.
Rough Endoplasmic Reticulum (RER): Protein synthesis and processing.
Smooth Endoplasmic Reticulum (SER): Lipid synthesis.
Golgi Apparatus: Protein processing.
Lysosomes: Digestion and recycling.
Peroxisomes: Oxidation of fatty acids.
Vacuoles: Storage of oils, carbs, waters, or toxins.
Mitochondria: ATP production.
Chloroplasts: ATP and sugar production via photosynthesis.
Cytoskeleton: Structural support and cell movement.
Plasma Membrane: Selective permeability, maintains a suitable intracellular environment, and provides structural support.
Cell Wall: Protection and structural support (in plant cells).

RNA Granules

Nucleoprotein granules that contain RNA and proteins
Important for cellular function in nucleus and cytoplasm
Disintegrate when RNase-L activates.

Lipid Droplets

Considered organelles now.
Molecular aggregates found in cells.

Composition of Membranes

Membranes are composed of lipids, proteins, and carbohydrates.
Glycerophospholipids make up 3 classes of lipids.
Sterols, sphingolipids, and glycerophospholipids are lipids.
Proteins (including glycoproteins and glycolipids), are also components.
The lipid to protein ratio affects the biological activity of membranes.

Glycerophospholipids (GPLs)

Glycerol is the backbone of GPLs.
The head group is attached to the phosphate group of glycerol by an ester-linkage.
Fatty acid tails are attached to positions C-1 and C-2.

Polyunsaturated Fatty Acids (PUFAs)

Examples are EPA, DHA, and arachidonic acid.
More than one double bond (db)
Numbering starts at the carboxyl end (COOH)
"Omega-#" numbering starts at the methylated end (CH3)

Unsaturation Effects

More unsaturated FAs= decrease in melting temperature.
This is due to the "bent chain" structure of unsaturated fatty acids.
This can lead to the decreased membrane viscosity in membranes.

Sphingolipids

"Backbone" sphingosine is an amino alcohol.

Membrane Lipids

Amphipathic (polar head, and nonpolar tail)
Hydrophobic effect= spontaneous assembly into structured in mixed lipid-water systems
Maximizes NP-NP and P-P interactions
Minimizes overall energy from water/low entropy
Organize into: bilayers, liposomes/vesicles, and micelles

Historical Perspectives

Overton= relation of membrane passage to chemical nature.
Danielli-Davson model= a sandwich-like model of membrane structure (globuler proteins above and below hydrophobic bilayer)
Robertson's unit membrane hypothesis= true about all cell membranes
Singer-Nicolson's fluid mosaic model: proteins "float" within plane of membrane, and can move freely within cell's bilayer
Detergents disrupt protein-lipid interactions and denature them (preventing protein and lipid interaction for separation via centrifugation)

General Composition

The composition of membranes vary in different cell types and subcellular compartments
Generally, proteins to lipid ratio is higher in higher biological activity.

Cell Compartmentalization and Functions

Cells are compartmentalized to optimize biochemical processes and protect cellular structures.

Protein Transport and Localization

Cytosolic proteins are destined to be translocated to mitochondria, are primarily unfolded.
These proteins are coated by chaperone proteins that maintain their unfolded state until reaching the mitochondria's interior and use specific signal sequences to target their desired destination.
The process usually requires some form of energy transfer.
The outer and inner membranes of the mitochondria have protein translocators (TOM and TIM).

Protein Signal Sequences

N-terminal signals initiate import into matrix
Hydrophobic signal= stops translocation when it binds to the TIM23 complex
Second signal= directly into the inner membrane using OXA complex.
Signal sequences give protein polarity.

Protein Sorting in the ER

Protein translation begins in cytosol, then mRNA is exported to the cytoplasm to be recognised by exportin proteins which then exits the nucleus.
The signal recognition protein (SRP) binding to a signal sequence on a growing polypeptide halts the translation.
This also targets the growing polypeptide chain into the ER lumen= co-translational translocation of protein into the ER.
ER signal sequences help transport protein complexes by recognising ribosomes or membrane into the ER
After synthesis, the polypeptide enters the ER lumen, and signal peptidase cuts of the signal sequence.

Vesicular Trafficking

Endocytosis: uptake of extracellular material into vesicles (e.g., clathrin-mediated endocytosis).
Exocytosis: release of material from vesicles to the extracellular environment (e.g., secretory vesicles).
Proteins and lipids are sorted in the ERs and Golgi complex based on addresses for sorting in different compartments.
Vesicles carry cargo as they are transported according to targeting signals
COP is used for sorting of vesicles directed from ER to Golgi and vice versa
The signal sequence is processed before the polypeptide enters the ER lumen

Protein Glycosylation

Glycosylation is critical in the ER and Golgi, involving the addition of sugars to proteins to modify their structure, function, and targeting
Various glycosylation types (N-linked, O-linked) occur with different pathways to form glycoprotein
Functions of glycosylation include quality control or protein folding, interaction, and delivery of proteins, and in some cases, altering the proteins’ solubility

Retrieval

ER-resident proteins (e.g., proteins with KDEL sequence) are retrieved from the Golgi complex to the ER by transport vesicles.

Hydrophobic effect

Lipids in aqueous solutions are driven by minimizing the free energy via formation into organized structures
Minimizes free energy and maximizes favorable interactions (polar-polar and nonpolar-nonpolar)

Biophysical Methods

Microscopy
Spectroscopy
X-ray diffraction
Biochemical methods (e.g., immunofluorescence and chemical modification)

Polarity

Establishing cell polarity in development involves asymmetric distribution of proteins and lipids. • Mechanisms of polarity include breaking symmetry, recruitment of specific proteins and polarisation of the cytoskeleton, and vesicles.

Cell Polarity and Maintenance

Cells maintain their polarity state through the interaction of proteins and lipids, and through the maintenance and reinforcement of polarized states through the establishment of polarity in various cellular functions

Cell Junctions

Various types of cell junctions like adherens junctions and desmosomes.
Cadherins= transmembrane proteins that facilitate cell-cell adhesion
Integrins= transmembrane proteins that facilitate cell-ECM adhesion
Junctions play critical roles in establishing and maintaining cell polarity

Polarized Cytoskeleton

Microtubules (MTs) are uniformly polarized and are responsible for directional transport in cells.
Reinforce polarity by establishing directionality and movement
Golgi, ER, and Nucleus position are consistent and directional depending on position in a cell.

Core PCP complex

Establishes and maintains planar cell polarity.

Signal Transduction and Cellular Communication

Signal transduction= instrumental in cellular adaptation and survival.
Exosomes= mechanisms for transfer of intracellular components.
Proteins= dynamic structural fluctuations.
Cellular and intercellular communication are driven by basic survival needs.
Cellular communication relies on signaling molecules.

Signal Transduction Contexts

Signal transduction is used by cells to adapt and survive.
Cells use several types and timing of signal transduction.
Cells use compartments to control signal and pathway.
Cells employ feedback loops and cross-talk between signaling pathways.
Biomolecular condensates serve as highly dynamic and specific signaling centres.

Types of Post-Translational Modifications (PTMs)

Acetylation, Methylation, Phosphorylation, Ubiquitination, Sumoylation, and S-nitrosylation can alter protein activity, localization, binding interactions, and even stability, all regulating its downstream function.

Cell Cycle Checkpoints

Ensure cell cycle progression is correct.
Stops cell cycle if there are any issues
Specific proteins are crucial to detect and respond to DNA errors and damages

Cell Cycle Regulation

Cyclin-dependent kinases (CDKs)= regulate cell cycle progression by phosphorylation of target proteins
Cell cycle checkpoints= ensure that errors don't progress to downstream stages= critical for preventing cell cycle progression in the presence of DNA damage

Pathways of DNA Damage Sensing and Repair

The recognition of DNA damage triggers a complex cascade of events to repair DNA.
This involves the activation of kinases such as ATM and ATR to phosphorylate proteins that eventually lead to cell cycle arrest/repair.

Apoptosis

Initiated by caspases- cysteine proteases that cleave specific cell substrates.
These enzymes result in cellular components being degraded and the cell is signalled to be eliminated (apoptosome)
Apoptosis is a critical mechanism for eliminating cells with damaged DNA, preventing their propagation.

Stem Cell Types and Differentiation

Totipotent (zygotes), Pluripotent (ES cells), Multipotent (hematopoietic), Oligopotent (neural), and unipotent stem cells (muscle, erythrocytes)= specific potency in differentiation
Differentiated by DNA methylation (open or closed chromatin); chemicals, mechanical forces, and cytokines
Cytokine, chemical or mechanical forces are used to promote or prevent differentiation.

Introduction to iPSCs

Induced pluripotent stem cells= normal somatic cells transformed to a stem cell (pluripotent) with 4 transcription factors.
Common delivery methods are adenovirus, lentivirus and sendaiviruses.

Basic Principles of Animal Research

Ethical rules must be followed in animal research.
Research should only be conducted if it follows ethical guidelines and is scientifically relevant.

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Description

Test your knowledge on the structure and function of biological membranes, particularly focusing on phospholipids. Explore topics such as the Danielli-Davison Model, cytoskeleton functions, and the role of lipids and proteins in membrane dynamics. This quiz is essential for understanding cellular biology and membrane biochemistry.