Biology Chapter: Cell Membrane and Types

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Questions and Answers

What is the primary function of ribosomes in a cell?

Energy production

Genetic material storage

Site of protein synthesis (correct)

Degradation of waste materials

Which structure in the cell is responsible for the assembly of ribosomes?

Nuclear envelope

Endoplasmic reticulum

Chromatin

Nucleolus (correct)

What form does DNA take when combined with proteins?

Gene clusters

Chromatin (correct)

Chromosomes

Nucleotides

What is the role of the nuclear envelope?

Controls movement of molecules across it Signup and view all the answers

How do primary lysosomes differ from secondary lysosomes?

Secondary lysosomes originate from primary lysosomes during digestion Signup and view all the answers

What is the endomembrane system primarily responsible for?

Protein processing and transport Signup and view all the answers

What are the primary components that ribosomes consist of?

Ribosomal RNA and proteins Signup and view all the answers

What role do lysosomes play during phagocytosis?

They hydrolyze macromolecules into monomers Signup and view all the answers

Which feature distinguishes eukaryotic cells from prokaryotic cells?

Larger size compared to prokaryotic cells Signup and view all the answers

What is the role of ribosomes in prokaryotic cells?

Site of protein synthesis Signup and view all the answers

Which structure helps bacteria adhere to other cells?

Fimbriae Signup and view all the answers

What component is primarily found in bacterial cell walls?

Peptidoglycan Signup and view all the answers

What is the primary function of the cytoskeleton in prokaryotic cells?

Maintaining cell shape Signup and view all the answers

What type of microscopy was initially used to study organelles?

Light microscopy Signup and view all the answers

Which of the following is a characteristic of prokaryotic cells?

Rigid cell wall outside the membrane Signup and view all the answers

Which function is NOT associated with the cell membrane?

Producing energy through respiration Signup and view all the answers

What is the primary function of ligands in relation to receptors?

Change receptor shape upon binding Signup and view all the answers

What is the significance of the dissociation constant (KD) in receptor-ligand interactions?

It indicates the binding strength of ligands to receptors. Signup and view all the answers

Which type of receptor is specifically designed to bind large or polar ligands?

Membrane receptors Signup and view all the answers

How do agonists function in receptor binding compared to ligands?

They bind to the receptor and promote the same effects as the ligand. Signup and view all the answers

What is 'cross talk' in the context of signaling pathways?

Interactions between multiple signaling pathways Signup and view all the answers

Which receptor class is responsible for the catalyzation of phosphorylation of proteins?

Protein kinase receptors Signup and view all the answers

What role do second messengers play in signal transduction cascades?

They act as intermediaries that amplify the signal. Signup and view all the answers

What is one of the main functions of gated ion channels in receptor signaling?

Regulate ion flow in and out of the cell Signup and view all the answers

What is the main role of the cytoskeleton in a cell?

It serves as a structural unit and helps maintain cell structure. Signup and view all the answers

What category of cytoskeletal proteins is primarily involved in the shape and motility of the cell?

Microfilaments Signup and view all the answers

Which function is NOT associated with the extracellular matrix?

Transports nutrients across the cell membrane. Signup and view all the answers

How do organelles move within the cell?

They are carried along microtubules by motor proteins. Signup and view all the answers

What is one of the major components of the extracellular matrix that provides structural support?

Fibrous proteins such as collagen. Signup and view all the answers

What do microtubules primarily facilitate within the cell?

They form the 'road' for transporting cellular components. Signup and view all the answers

What is the theory of endosymbiosis primarily focused on?

The development of cellular organelles from prokaryotic cells. Signup and view all the answers

Which of these correctly describes the role of intermediate filaments in a cell?

They provide mechanical support and tensile strength. Signup and view all the answers

What is the main function of a phosphorylation cascade in a signaling pathway?

It amplifies the signal through sequential protein activations. Signup and view all the answers

Which molecules are generated when PIP2 is hydrolyzed?

IP3 and DAG Signup and view all the answers

What does the term 'second messenger' typically refer to in signal transduction?

Small molecules that facilitate signal propagation inside the cell. Signup and view all the answers

How can phosphorylation affect proteins in signaling pathways?

It can cause both activation and inhibition of protein activity. Signup and view all the answers

What role do gap junctions play in signaling between cells?

They enable rapid transfer of ions and communication between cells. Signup and view all the answers

What response might a cell show when signaled to open ion channels?

Alteration in the permeability of the cell membrane. Signup and view all the answers

What is the significance of phosphorylation in cellular signaling?

It provides a simple means of regulation by adding or removing phosphates. Signup and view all the answers

How do cells generally respond to signaling molecules?

By activating various intracellular signals and pathways. Signup and view all the answers

Study Notes

Cell Membrane

The cell membrane controls what enters and leaves the cell
It helps maintain a constant internal environment
It plays a role in communication and receiving signals
It often has proteins for binding and adhering to adjacent cells

Cell Types

Prokaryotic cells lack membrane-enclosed internal compartments
- Examples: bacteria and archaea
Eukaryotic cells contain membrane-enclosed organelles
- Examples: plants, animals, fungi

Prokaryotic Cells

Enclosed by a cell membrane
DNA is located in a region called the nucleoid
Cytoplasm contains the rest of the cell's contents
Ribosomes are the site of protein synthesis
Most prokaryotes have a rigid cell wall outside of the cell membrane
Bacteria cell walls contain peptidoglycan, and some have an additional outer membrane
Some bacteria have a slimy capsule of polysaccharides
Photosynthetic bacteria have an internal membrane system containing molecules needed for photosynthesis
Cytoskeleton maintains cell shape and plays a role in cell movement and cell division
Some prokaryotes swim using flagella, composed of flagellin
Pili help bacteria adhere to other cells
Fimbriae are shorter structures that help bacteria adhere to surfaces

Eukaryotic Cells

About 10 times larger than prokaryotic cells
Membrane-enclosed organelles carry out specific functions
Most eukaryotic cells have similar organelles
Organelles were first studied using light microscopy and then electron microscopy
Specific stains target molecules to determine the chemical composition of organelles
Cell fractionation separates organelles by size or density for chemical analysis

Ribosomes

The site of protein synthesis
Similar structure in prokaryotes and eukaryotes
Consist of two subunits: ribosomal RNA (rRNA) and more than 50 different proteins

Nucleus

Usually the largest organelle
Contains most of the cell's DNA
Site of DNA replication
Site where gene transcription is turned on or off
Assembly of ribosomes begins in a region called the nucleolus
Surrounded by the nuclear envelope, a double membrane
Nuclear pores control the movement of molecules across the envelope
The outer membrane is continuous with the endoplasmic reticulum
DNA combines with proteins to form chromatin in long, thin threads called chromosomes
Before cell division, chromatin condenses, and individual chromosomes become visible under a light microscope

Plant Cells

Have cell walls
Have certain vacuoles that store small molecules in water and add stiffness to the structure
Contain chloroplasts where photosynthesis occurs

Endomembrane System

An interconnected system of membrane-enclosed compartments
Allows for the proper processing of proteins and coordinates protein folding
Tiny, membrane-surrounded vesicles shuttle substances between various components
Membranes and their contents are in constant motion

Lysosomes

Contain digestive enzymes that hydrolyze macromolecules into monomers
Break down large macromolecules and their components into building blocks for new molecules
Originate from the Golgi apparatus

Food Digestion (Endocytosis)

Food molecules enter the cell by phagocytosis, forming a phagosome
Phagosomes fuse with primary lysosomes to form secondary lysosomes
Enzymes in secondary lysosomes hydrolyze food molecules

Waste Removal (Exocytosis)

Waste is ejected by exocytosis

Cytoskeleton

Serves as a structural unit within the cell
Helps maintain cell structure, movement, and organization of internal components
Composed of three major categories of cytoskeletal proteins: microtubules, microfilaments, and intermediate filaments

Microtubules

Structures found dispersed throughout the cell
Act as the "road" for the cell, with all things inside attaching to them
Form the infrastructure of the cell

Microfilaments

Determine the shape of the cell
Allow for motility and movement of the cell

Intermediate Filaments

Underline the structure of the cell

Organelle Movement Within the Cell

Things are carried within the cell along microtubules (the "road") by motor proteins
Motor proteins are responsible for translocation across microtubules through either the positive or negative ends
Motor proteins cannot move on their own

Extracellular Matrix

Holds cells together in tissues
Contributes to the properties of bone, cartilage, and skin
Filters materials passing between different tissues
Orients cell movements during development and tissue repair
Plays a role in chemical signaling
Composed of fibrous proteins like collagen, gel-like proteoglycans, and other proteins

Cell Wall

Composed of extracellular matrix proteins
Rigid but flexible support for plants
Barrier against disease organisms
Contributes to plant form as growing cells expand

Endosymbiosis Theory

Proposes that mitochondria and plastids arose when one cell engulfed another cell

Signal Transduction

Cells respond to chemical signals from inside or outside the cell

Signal Transduction Pathway

Begins with a signal that binds to a receptor protein, initiating a cascade of events within the cell
Leads to a specific cellular response

Receptor Proteins

Have specific binding sites for chemical signal molecules, called ligands
Ligands fit a three-dimensional site on the receptor, causing a change in shape
Binding is reversible and the ligand is not altered

Cross Talk

Interactions between multiple signaling pathways
One pathway might turn on a cellular response, while another turns it off
Occurs within and between different signaling pathways

Agonists

Have the same effect as the ligand, stimulating a response

Antagonists (Inhibitors)

Bind to the receptor, preventing the ligand from binding and inhibiting the signal transduction pathway

Cellular Response

The effect of a signaling pathway on the cell

Receptor Kd

Dissociation constant, a measure of the affinity between a receptor and its ligand
Lower Kd indicates higher affinity
Some receptors have very low Kd values, allowing them to bind at very low ligand concentrations

Medical Relevance of Receptor Kd

Drugs can function as ligands
Kd is important for determining dosages, minimizing harm, and maximizing effectiveness

Membrane Receptors

Bind large or polar ligands (e.g., insulin)
Located outside the cell

Intracellular Receptors

Bind small or nonpolar ligands that can diffuse across the cell membrane (e.g., estrogen.)

Receptor Classes in Eukaryotes

Gated ion channels: Allow ions to enter or leave the cell
Protein kinase receptors: Catalyze phosphorylation of themselves and/or other proteins, causing a change in conformation.
G protein-coupled receptors: Signal binding activates a G protein, which then activates an effector protein.

Cascade in the Signal Transduction Pathway

Amplifies the signal through a series of events involving multiple proteins
A single activated receptor can initiate signaling across many proteins, leading to the activation of other proteins downstream
The cascade results in signal amplification

Second Messengers

Small molecules that mediate some steps in a cascade
Often involved in relaying the signal from the activated receptor to initiate the signaling cascade inside the cell

PIP2

A membrane phospholipid that can be hydrolyzed into two secondary messenger molecules:
- IP3 (released into the cytoplasm)
- DAG (remains in the membrane)

Role of Phosphorylation in Signaling Pathways

Protein modification where a phosphate group can be added to a protein
Addition of a phosphate group can either activate or inhibit a protein
Phosphorylation often plays a role in signal transduction pathways, leading to specific cellular responses

Cell Junctions and Signal Transduction

Gap junctions are ion channels that allow the rapid movement of ions between cells
These junctions facilitate communication between cells

Cellular Responses to Signals

Opening ion channels
Changing enzyme activity
Differential gene expression

Role of Intracellular Communication in Multicellular Life

Facilitates the development and function of complex multicellular organisms
Allows for coordinated actions between different cells, contributing to organismal processes

Hormones

Travel to distant cells, usually through the circulatory system
Act as ligands, binding to receptor proteins on target cells

Summary of Cell Signaling

Cells have various signaling pathways
Signals can originate from inside or outside the cell
Signaling pathways involve a cascade of events and second messengers
Signal transduction leads to specific cellular responses that allow cells to interact and function within a greater context

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Description

Explore the fundamental aspects of cell membranes and the differences between prokaryotic and eukaryotic cells. Understand how the cell membrane functions to control entry and exit, and the unique characteristics of prokaryotic cells. This quiz covers essential concepts necessary for mastering cellular biology.