Biology Organelles and Cell Membrane

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Questions and Answers

What is the primary function of mitochondria in the cell?

Cell division

ATP synthesis (correct)

Protein synthesis

Waste removal

What is the folded internal membrane of mitochondria called?

Cristae (correct)

Matrix

Cytoplasm

Outer membrane

In what part of the mitochondria does the citric acid cycle occur?

Matrix (correct)

Cytoplasm

Outer membrane

Cristae

Which process generates the most ATP during aerobic respiration?

Electron transport system Signup and view all the answers

What type of protein forms the smallest elements of the cytoskeleton?

Actin Signup and view all the answers

Which cytoskeletal element is known for its strength and durability?

Intermediate filaments Signup and view all the answers

What is the diameter range of intermediate filaments?

7 to 11 nm Signup and view all the answers

What characterizes membranous organelles?

They are completely enclosed by a membrane. Signup and view all the answers

From where do microtubules extend in the cell?

Centrosome Signup and view all the answers

Which of the following is a non-membranous organelle?

Ribosomes Signup and view all the answers

What is the primary structure of the plasma membrane?

Phospholipid bilayer Signup and view all the answers

Integral proteins in the plasma membrane are primarily responsible for which function?

Creating channels for solute transport Signup and view all the answers

Which statement about peripheral proteins is true?

They are easily separated from the membrane. Signup and view all the answers

What role do anchoring proteins play in the plasma membrane?

Attaching the plasma membrane to other structures Signup and view all the answers

What function do recognition proteins serve in the plasma membrane?

Detecting molecules in the immune system Signup and view all the answers

What distinguishes transmembrane proteins from other integral proteins?

They span the entire membrane. Signup and view all the answers

What is the role of a solvent in a solution?

It dissolves the solutes. Signup and view all the answers

Which of the following is NOT a factor influencing diffusion rates?

Density of the solution Signup and view all the answers

What occurs during facilitated diffusion?

A carrier protein assists molecules that are too large to pass through phospholipids. Signup and view all the answers

How does osmotic pressure affect the movement of pure water?

It indicates the force with which water moves into the solution. Signup and view all the answers

What is the primary characteristic of an isotonic solution?

Equal solute concentration with the cell. Signup and view all the answers

What happens to animal cells in a hypertonic solution?

They lose water and may crenate. Signup and view all the answers

What is the difference between osmolarity and tonicity?

Osmolarity refers to solute concentration, while tonicity refers to the effect of the solution on the cell. Signup and view all the answers

Which process described requires the input of energy?

Active processes Signup and view all the answers

What structural arrangement is found in cilia?

Nine doublets forming a cylinder Signup and view all the answers

Which structure is responsible for the synthesis of proteins?

Ribosomes Signup and view all the answers

What is the primary function of the nucleus?

To act as the control center for cellular operations Signup and view all the answers

What are microvilli used for in a cell?

Increasing surface area for absorption Signup and view all the answers

What is the nuclear envelope?

A double membrane surrounding the nucleus Signup and view all the answers

Which of the following statements about centrioles is true?

They help form spindle fibers during cell division Signup and view all the answers

How do nuclear pores function?

They facilitate communication between the nucleus and the cytosol Signup and view all the answers

Which of the following correctly describes triplets in microtubules?

Nine microtubules forming an arrangement in the centriole Signup and view all the answers

What occurs during translocation in protein synthesis?

A ribosome moves down the mRNA strand. Signup and view all the answers

What does the stop codon signify during elongation?

The completion of a polypeptide chain. Signup and view all the answers

Which phase of the cell cycle involves DNA replication?

S phase Signup and view all the answers

What role does helicase play during DNA replication?

It unwinds and unzips the DNA. Signup and view all the answers

In which stage of the cell cycle do cells prepare for division by making necessary proteins?

G2 phase Signup and view all the answers

What is produced from the lagging strand during DNA replication?

Okazaki fragments Signup and view all the answers

What is the outcome of semi-conservative replication?

Each daughter DNA strand contains one original and one new strand. Signup and view all the answers

What occurs during prophase in mitosis?

Chromosomes condense and the nuclear membrane breaks down. Signup and view all the answers

Study Notes

Organelles

Two types of organelles: membranous and non-membranous
Membranous Organelles: enclosed by a phospholipid membrane
- Examples: mitochondria, nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes
Non-Membranous Organelles: not enclosed by a membrane, components are in direct contact with the cytosol
- Examples: cytoskeleton, centrioles, microvilli, cilia, flagella, and ribosomes

Cell Membrane

Forms a barrier between the cell and its environment
Consists of a phospholipid bilayer with scattered proteins
- Phospholipid Bilayer:
  - Thin and delicate (6-10 nm)
  - Hydrophilic heads face outward, hydrophobic tails face inward
  - Creates a barrier between the cytoplasm and extracellular fluid
- Proteins:
  - Integral Proteins: embedded in the membrane, pass all the way through (transmembrane proteins), can form channels or pores
  - Peripheral Proteins: bound to the inner or outer surface of the membrane, easily separated
- Functional Classes of Membrane Proteins:
  - Anchoring Proteins: connect the plasma membrane to other structures
  - Recognition Proteins: recognized by cells of the immune system
  - Receptor Proteins: bind to specific extracellular molecules (ligands)
Diffusion: movement of molecules from an area of high concentration to low concentration
- Factors Influencing Diffusion Rate: distance, molecule size, temperature, gradient size, electrical forces
- Facilitated Diffusion: transport of large molecules with the help of carrier proteins (no ATP required)
- Osmosis: diffusion of water across a selectively permeable membrane from an area of high water concentration to low concentration
Osmotic Pressure: force with which pure water moves into a solution due to solute concentration
Osmolarity: solute concentration of a solution
Tonicity: effect of a solution on a cell
- Isotonic: equal solute concentration inside and outside the cell (no net movement)
- Hypertonic: higher solute concentration outside the cell (water moves out, cell shrinks)
- Hypotonic: lower solute concentration outside the cell (water moves in, cell swells)
Filtration: bulk flow of substances driven by a pressure gradient (no ATP required)
Active Processes: require energy (ATP)

Mitochondria

Powerhouses of the cell
Responsible for ATP synthesis
Double-layered membrane
- Cristae: folded inner membrane, increases surface area for ATP production
- Matrix: liquid enclosed by the inner membrane
Aerobic Respiration: multi-step process for ATP production
- Glycolysis: glucose breakdown into pyruvate (occurs in cytoplasm, produces 2 ATP)
- Citric Acid Cycle: pyruvate breakdown into carbon dioxide, hydrogen, and 2 ATP (occurs in mitochondrial matrix)
- Electron Transport System: hydrogen atoms used to create 32 ATP, oxygen combines with hydrogen to form water

Cytoskeleton

Provides internal framework, strength, and flexibility
Composed of microfilaments, intermediate filaments, and microtubules
- Microfilaments: smallest, primarily composed of actin, found in the cell periphery
- Intermediate Filaments: strong and durable, various protein types, present throughout the cytoplasm
- Microtubules: largest, extend from the centrosome, involved in cell division

Centrioles

Cylindrical structures composed of microtubules arranged in nine triplets
Located at the centrosome
Involved in cell division, forming spindle fibers that move chromosomes to the poles

Cilia

Long, slender extensions for propelling fluids or solids
Microtubules arranged in nine doublets around a central pair

Microvilli

Finger-shaped extensions of the plasma membrane
Core of microfilaments for stiffness
Increase surface area for nutrient absorption

Ribosomes

Responsible for protein synthesis
Consist of two subunits: small and large
Attached to the endoplasmic reticulum

Nucleus

Control center of the cell
Contains genetic information (DNA)
Directs protein synthesis
Usually the largest and most prominent structure in the cell
Nuclear Envelope: surrounds the nucleus, double membrane with pores
- Nuclear Pores: allow communication between the nucleus and cytoplasm

DNA Replication

Process of duplicating DNA
Occurs during the S-phase of the cell cycle
Steps:
- Helicase: unwinds and unzips the DNA
- DNA Polymerase: adds complementary nucleotides to create two daughter strands
- Lagging Strand: synthesized discontinuously, forming Okazaki fragments that are glued together by Ligase
- Leading Strand: synthesized continuously
- Semi-Conservative Replication: each daughter strand has one original and one new strand
Sister Chromatids: two identical strands of DNA connected at the centromere
- Kinetochore: raised region on the centromere where spindle fibers attach

Cell Cycle

Cycle of growth and division
Interphase:
- G1: cell growth, normal functions, organelle duplication
- S: DNA replication
- G2: preparation for division
- G0: a resting state where cells permanently stop dividing
M Phase: mitosis and cytokinesis
Mitosis: identical nuclear division in somatic cells (body cells), for repair and replacement
- Prophase: nuclear membrane breaks down, chromosomes condense, spindle fibers form
- Metaphase: chromosomes line up at the equator of the cell, attached to spindle fibers at the kinetochore
- Anaphase: sister chromatids separate and move to opposite poles
- Telophase: nuclear membrane reforms, chromosomes decondense, cytokinesis begins
Meiosis: nuclear division in sex cells (gametes), resulting in genetically diverse daughter cells

Protein Synthesis

Steps:
- Transcription: DNA is copied into mRNA
- Translation: mRNA is translated into a polypeptide chain by ribosomes
  - mRNA: messenger RNA, carries the genetic code from DNA to ribosomes
  - tRNA: transfer RNA, carries amino acids to the ribosomes
  - Ribosome: reads mRNA and assembles amino acids into a polypeptide
  - Codon: three-nucleotide sequence on mRNA that specifies an amino acid
  - Anticodon: three-nucleotide sequence on tRNA that complements a codon
  - Elongation: process of adding amino acids to the polypeptide chain
  - Translocation: shift of tRNA from one site on the ribosome to another
  - Chain Termination: stop codon signals the ending of polypeptide synthesis
Polypeptide Folding: polypeptide chain folds into a specific three-dimensional shape to become a functional protein
Protein Structure: primary, secondary, tertiary, and quaternary

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Description

Test your knowledge on the various types of organelles, including membranous and non-membranous structures. This quiz also covers the essential functions and composition of the cell membrane, highlighting its importance in cellular processes. Brush up on your biology concepts!