General Zoology Lecture 4: Ribosomes

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Questions and Answers

What is the main function of free ribosomes in an animal cell?

Synthesis of proteins for release outside the cell

Catalyzing the formation of peptide bonds

Synthesis of proteins that are used within the cell (correct)

Decoding mRNA during protein synthesis

Which of the following describes the role of the large ribosomal subunit in protein synthesis?

Catalyzing the formation of peptide bonds between amino acids (correct)

Binding mRNA to initiate translation

Decoding transfer RNA molecules

Translating mRNA into amino acid sequences

What determines the type of protein synthesized by a ribosome in a cell?

The type of amino acids available

The location of the ribosome within the cell (correct)

The availability of mRNA molecules

The size of the ribosome

How do ribosomal subunits behave during the synthesis of a specific protein?

They are temporarily assembled and disassembled Signup and view all the answers

What are the three sites present in the large ribosomal subunit for tRNA association?

A, P, E Signup and view all the answers

What is primarily the function of the small ribosomal subunit?

To decode mRNA sequences Signup and view all the answers

What occurs when multiple ribosomal subunits admit an mRNA molecule?

A polysome structure is formed Signup and view all the answers

Which type of ribosome is associated with the endoplasmic reticulum?

Attached ribosome Signup and view all the answers

What is the first stage in the assembly of intermediate filaments?

Formation of dimers Signup and view all the answers

Which statement about the structure of intermediate filaments is true?

They are characterized by a rope-like structure of eight protofilaments. Signup and view all the answers

Which function is NOT associated with intermediate filaments?

Facilitate intracellular transport Signup and view all the answers

How are tubulin subunits characterized in microtubules?

They are assembled from GTP-αβ tubulin heterodimers. Signup and view all the answers

What distinguishes the assembly process of intermediate filaments from that of actin filaments and microtubules?

Intermediate filaments are apolar. Signup and view all the answers

Which network is formed by intermediate filaments in a cell?

Connecting network for cell attachment Signup and view all the answers

What is the diameter of microtubule fibers?

25 nm Signup and view all the answers

Which motor proteins are associated with the function of microtubules?

Kinesin and dynein Signup and view all the answers

What is the first stage in the assembly of microtubules?

Nucleation Signup and view all the answers

Which protein is responsible for the transport of organelles along microtubules?

Kinesin Signup and view all the answers

What is the primary purpose of cilia in mammalian cells?

To move substances around the cell Signup and view all the answers

How many protofilaments wrap around to form the circular structure of a microtubule?

13 Signup and view all the answers

What constitutes the internal core of a cilium?

Axoneme Signup and view all the answers

Which component of the microtubule structure is GTP-bound in its β-subunit?

β-tubulin Signup and view all the answers

What is one major structural difference between cilia and flagella?

Cilia are shorter and more numerous Signup and view all the answers

How do protofilaments assemble into a microtubule?

By lateral association and stabilization Signup and view all the answers

What determines the shape of cells according to Nikolai Koltsov's proposal?

The cytoskeleton Signup and view all the answers

Which of the following correctly lists the main types of cytoskeletal components in eukaryotic cells?

Microfilaments, Intermediate filaments, Microtubules Signup and view all the answers

Which function of the cytoskeleton relates to the transport of organelles?

Intracellular transport Signup and view all the answers

How does the cytoskeleton contribute to cell motility in single-celled organisms?

Through the use of cilia or flagella Signup and view all the answers

What is the role of the active site within the ribosome?

Linking amino acids to form peptide bonds Signup and view all the answers

Which statement about the cytoskeleton's capability is accurate?

It can rapidly grow or disassemble based on cellular needs. Signup and view all the answers

What is NOT a function of the cytoskeleton?

Energy conversion Signup and view all the answers

Which of the following best describes the protein filaments forming the cytoskeleton?

Dynamic structures composed of identical proteins Signup and view all the answers

What is the motor protein found in microtubule A of cilia?

Dynein Signup and view all the answers

What is the arrangement of microtubules at the proximal end of the basal body?

9 + 0 arrangement of triplet microtubules Signup and view all the answers

Which statement is true regarding the structure of centrioles?

Together with the basal body, they form the microtubule organizing center (MTOC). Signup and view all the answers

Which of the following describes the centriole's microtubule arrangement?

Centrioles consist of nine triplets of microtubules arranged in a ring. Signup and view all the answers

What is the relationship between centrioles and centrosomes?

Centrosomes consist of two centrioles positioned perpendicular to each other. Signup and view all the answers

What role does the dynein motor protein play in the structure of microtubules?

It helps the microtubules slide along each other when ATP is present. Signup and view all the answers

Which statement accurately describes the arrangement of microtubules in the basal body?

It consists of a 9 + 0 arrangement of triplet microtubules at the proximal end. Signup and view all the answers

What structure prevents lengthwise sliding of microtubule doublets in a cilium?

Nexin and radial spokes Signup and view all the answers

What is the primary location of centrosomes?

Near the nucleus in animal cells. Signup and view all the answers

Which of the following describes the structure of centrioles within a centrosome?

Arranged as 9 triplets of microtubules in a ring formation. Signup and view all the answers

What is the function of centrioles in relation to cilia and flagella?

They act as basal bodies during the formation of cilia and flagella. Signup and view all the answers

How do radial spokes function in microtubule organization?

They provide structural support to microtubule doublets. Signup and view all the answers

What type of protein is nexin in relation to microtubules?

A structural protein linking adjacent microtubule doublets. Signup and view all the answers

Study Notes

General Zoology (1) - Lecture 4

Ribosomes:
- Found in both prokaryotic and eukaryotic cells
- In eukaryotes, also found in mitochondria and chloroplasts
- Prokaryotic ribosomes are generally smaller than eukaryotic
- Function as a "micro-machine" for protein synthesis
- About 10 billion protein molecules in a mammalian cell, and ribosomes produce all of them
Ribosome Structure:
- Formed from two subunits: large and small ribosomal subunits
- The two subunits are not equal in size, with the large subunit being approximately twice the size of the small subunit
- Exist in a free state (not attached) until required for use
Ribosome Molecular Structure:
- Composed of nucleic acids and proteins
- Ribosomal RNA (rRNA) accounts for approximately two-thirds of the ribosome's mass
- Ribosomal proteins account for approximately one-third of the mass
Ribosome Synthesis:
- Proteins and rRNA that form the ribosomal subunits are made in the nucleolus
- Exported through nuclear pores into the cytoplasm
Prokaryotic vs. Eukaryotic Ribosomes:
- Prokaryotic ribosomes have an Svedberg value of 70S
- Eukaryotic ribosomes have an Svedberg value of 80S
Types of Ribosomes in Animal Cells:
- Free ribosomes: Floating freely in the cytoplasm, synthesizing proteins used within the cell
- Attached ribosomes: Attached to the endoplasmic reticulum, synthesizing proteins for intracellular or extracellular use
Function of Ribosomal Subunits in Protein Synthesis:
- Small subunit: Decoding function, links with mRNA and attaches to the larger subunit.
- Large subunit: Catalytic function (catalyzing peptide bond formation between amino acids)
- Ribosomal RNA (rRNA) performs the function of an enzyme in the large subunit
Ribosomal Subunits Are Not Static:
- Separate after protein production
Location of Ribosomes in a Cell Determines Protein Type:
- Location within the cell determines the proteins synthesized
Ribosomal Subunit Sites:
- A (aminoacyl) site
- P (peptidyl) site
- E (exit) site

Cytoskeleton

Introduction:
- Cytoskeleton proposed in 1903 by Nikolai Koltsov
- A complex dynamic network of interlinking protein filaments present in the cytoplasm of all cells
- Extends from the cell nucleus to the cell membrane
- Composed of similar proteins in various organisms
Types of Cytoskeletal Filaments:
- Microfilaments
- Intermediate filaments
- Microtubules
General Functions of Cytoskeleton:
- Provides structural support
- Facilitates intracellular transport of vesicles and organelles
- Enables cell motility (e.g., crawling movement in Amoeba, cilia/flagellar movement in Paramecium)
- Enables motility in multicellular organisms (e.g. muscle contraction, movement of sperm, white blood cells, and phagocytes)
- Plays a critical role in cell division, aiding in chromosome alignment and separation (cytokinesis)

Microfilaments (Actin Filaments)

Structure:
- Solid protein rods
- Composed of actin protein
- 7 nm in diameter; Smallest cytoskeletal filament
- Two strands wound in a spiral shape
- Individual actin molecules are referred to as G-actin (Globular actin)
- F-actin (Filamentous actin): The polymerized form that is two strands intertwined
Polymerization Steps:
- Nucleation: G-actin with ATP binds to form ATP-bound actin monomers that aggregate to form short oligomers (nuclei)
- Elongation: Nuclei elongate from both ends through addition of ATP-actin monomers
- Stationary and Steady States: The elongating F-actin is relatively stable; ATP-bound actin hydrolyzes to ADP-bound actin at the negative end. Tropomyosin and cap Z proteins will stabilize the actin filaments and prevent depolymerization

Intermediate Filaments

Function:
- Provides structural support and flexibility within animal cells.
Structure:
- 10-12 nm in diameter
- Composed of 70 different fibrous protein subunits
- Subunits classified by tissue distribution
- Includes:
  - Nuclear lamina (in the nucleus)
  - Acidic and basic keratins (in the skin epithelium)
Assembly:
- Dimers -> Tetramers -> Protofilaments -> Filaments
- Apolar filaments (no distinct plus or minus ends)

Microtubules

Structure:
- Stiff, hollow, unbranched, and inextensible tubes
- 25 nm in diameter
- Made up of protein subunits: a-tubulin and b-tubulin (GTP-bound) heterodimers
- A-tubule contains a motor protein called dynein.
- B-tubule linked to A-tubule through nexin.
Function:
- Intracellular transport (e.g., vesicles along the ER, Golgi apparatus, plasma membrane)
- Organelle movement
- Associated with motor proteins (kinesin and dynein)
- Form spindle fibers (important for cell division)
- Form cilia and flagella
Assembly:
- Protofilaments -> Sheets -> Tubes (13 protofilaments)
- Nucleation and Elongation (growth from both ends)

Cilia and Flagella Structure

Axoneme:
- Composed of microtubules
- 9 pairs of microtubules surrounding 2 central microtubules (9+2 arrangement)
- Dynein arms and nexin link proteins connect the microtubules
Basal Bodies:
- 9+0 arrangement of triplet microtubules (at base) that form during cilium development and are identical in structure to centrioles

Centrosome

Location: Near the nucleus in animal cells
Structure: Contains two centrioles at right angles to each other(orthogonal)

General Information on protein synthesis for ribosomes

Ribosomes are critical for protein synthesis
Ribosome location affects the proteins they synthesize
The structure of ribosomes includes a large and small subunit
Ribosome assembly is not permanent; they separate once protein production is complete
Various cellular components are involved in protein synthesis.

Other Information

The given text describes various types of cellular structures and their roles
Different arrangements of microtubules characterize cilia, flagella, basal bodies, and centrioles.
Many cellular structures/components are mentioned such as ribosomes, cytoskeleton, microfilaments, intermediate filaments and microtubules.
The dynamic nature of some proteins, like microtubules, which are associated with motor proteins is also mentioned.

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Description

Explore the essential role of ribosomes in both prokaryotic and eukaryotic cells in this quiz on General Zoology. Learn about their structure, molecular composition, and the process of protein synthesis. Test your understanding of ribosomal function and significance in cell biology.