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During Prophase I of Meiosis I, what occurs to the chromosomes?

  • They uncoil and become diffuse.
  • They move to the poles of the cell.
  • They condense and become visible. (correct)
  • They replicate to form duplicate chromosomes.

    • What is a key difference between Meiosis I and Mitosis?

  • Meiosis I produces four diploid cells.
  • Meiosis I occurs in somatic cells.
  • Meiosis I has two successive cell divisions.
  • Homologous chromosomes align together in Meiosis I. (correct)

    • During Metaphase I of Meiosis I, what occurs to the chromosomes?

  • They move to the poles of the cell.
  • They uncoil and become diffuse.
  • They replicate to form duplicate chromosomes.
  • They align in the middle of the cell. (correct)

    • What is the result of Meiosis II?

    <p>Four haploid cells with unpaired sister chromatids.</p> Signup and view all the answers

    What attaches to the kinetochores during Meiosis I?

    <p>Chromosomes</p> Signup and view all the answers

    During Anaphase I of Meiosis I, what occurs to the chromosomes?

    <p>Homologous chromosomes separate.</p> Signup and view all the answers

    What occurs to the sister chromatids during Meiosis I?

    <p>They remain attached at the centromere.</p> Signup and view all the answers

    During Prophase I of Meiosis I, what process can occur between homologous chromosomes?

    <p>Crossing over</p> Signup and view all the answers

    What is the main purpose of meiosis?

    <p>For reproduction</p> Signup and view all the answers

    How many daughter cells are produced in meiosis?

    <p>4</p> Signup and view all the answers

    What occurs during synapsis in meiosis I?

    <p>Crossing over</p> Signup and view all the answers

    What is the role of kinetochores in meiosis?

    <p>Attached to microtubules</p> Signup and view all the answers

    What is the main difference between meiosis I and meiosis II?

    <p>Number of chromosome sets</p> Signup and view all the answers

    What is the outcome of crossing over during meiosis I?

    <p>Genetic diversity</p> Signup and view all the answers

    What is the primary function of chromosome condensation in meiosis?

    <p>To prepare chromosomes for separation</p> Signup and view all the answers

    What is the stage of meiosis that resembles mitosis?

    <p>Meiosis II</p> Signup and view all the answers

    During which stage of Meiosis I do homologous chromosomes join together at regions called chiasmata?

    <p>Prophase I</p> Signup and view all the answers

    What is the primary difference between Meiosis I and Mitosis?

    <p>Homologous chromosomes joining together</p> Signup and view all the answers

    What is the term for the regions where homologous chromosomes are swapped during Meiosis I?

    <p>Chiasmata</p> Signup and view all the answers

    During which stage of Meiosis do chromosomes condense?

    <p>Prophase I</p> Signup and view all the answers

    What is the term for the process of swapping regions of homologous chromosomes during Meiosis I?

    <p>Crossing over</p> Signup and view all the answers

    What is the stage of Meiosis that follows Meiosis I?

    <p>Meiosis II</p> Signup and view all the answers

    What is the term for the region where microtubules attach to chromosomes during Meiosis?

    <p>Kinetochores</p> Signup and view all the answers

    During which stage of Meiosis do nuclear envelopes break down?

    <p>Prophase I</p> Signup and view all the answers

    What is the primary function of ligand-gated ion channel receptors?

    <p>To allow the flow of specific ions into the cell</p> Signup and view all the answers

    What is unique about the structure of G protein-coupled receptors?

    <p>They are associated with the plasma membrane</p> Signup and view all the answers

    What is the primary function of enzyme-coupled receptors?

    <p>To catalyze enzymatic reactions</p> Signup and view all the answers

    What is the characteristic of steroid receptors?

    <p>They are cytoplasmic receptors</p> Signup and view all the answers

    Which type of receptor is involved in the signaling system described in Fig. 11.07?

    <p>G Protein-coupled Receptors</p> Signup and view all the answers

    What is the role of GTP in the G protein-coupled receptor signaling system?

    <p>To activate the G protein</p> Signup and view all the answers

    What is the significance of the gate returning to the closed position in ligand-gated ion channel receptors?

    <p>It prevents the constant activation of the next nerve cell</p> Signup and view all the answers

    What is the result of the signaling system returning to the resting state?

    <p>The system is reset and the receptor returns to its original shape</p> Signup and view all the answers

    What percentage of human proteins are cell-surface receptors?

    <p>30%</p> Signup and view all the answers

    What is an example of a G protein-coupled receptor?

    <p>Adrenaline receptor</p> Signup and view all the answers

    What is the significance of G protein-coupled receptors in humans?

    <p>They are involved in the response to 60% of drugs</p> Signup and view all the answers

    What is an example of a ligand that binds to ligand-gated ion channel receptors?

    <p>Dopamine</p> Signup and view all the answers

    What is the role of GDP in the G protein-coupled receptor signaling system?

    <p>To deactivate the G protein</p> Signup and view all the answers

    What is the function of the enzyme activated by the G protein?

    <p>To trigger a cellular response</p> Signup and view all the answers

    What is the result of the G protein binding to the receptor?

    <p>The receptor shape changes to allow the G protein to bind</p> Signup and view all the answers

    What is the role of the ligand in the G protein-coupled receptor signaling system?

    <p>To bind to the receptor and trigger a response</p> Signup and view all the answers

    What is the primary mechanism by which thermoreceptors in the skin detect heat signals?

    <p>by changing shape to allow ions to flow through</p> Signup and view all the answers

    What type of signalling molecule is estrogen?

    <p>Lipid-soluble</p> Signup and view all the answers

    What is the primary function of signal transduction in cellular signalling?

    <p>to convert the signal into a response</p> Signup and view all the answers

    What is the term for the process by which a signalling molecule binds to a receptor and changes its shape?

    <p>Signal reception</p> Signup and view all the answers

    What is the primary characteristic of long-distance signalling, also known as endocrine signalling?

    <p>It is mediated by hormones</p> Signup and view all the answers

    What is the term for the type of signalling that involves the release of signalling molecules from one cell and their binding to receptors on nearby cells?

    <p>Paracrine signalling</p> Signup and view all the answers

    What is the primary function of cell junctions in direct cell-to-cell signalling?

    <p>to allow direct communication between cells</p> Signup and view all the answers

    What is the term for the type of signalling that involves the release of signalling molecules from one cell and their binding to receptors on distant cells?

    <p>Endocrine signalling</p> Signup and view all the answers

    What is the primary function of the G protein in the G protein-coupled receptor signaling system?

    <p>To activate the enzyme that triggers a cellular response</p> Signup and view all the answers

    What happens to the G protein when it binds to GTP?

    <p>It becomes active</p> Signup and view all the answers

    What is the result of the G protein hydrolyzing GTP to GDP?

    <p>The signaling system is turned off</p> Signup and view all the answers

    What type of receptor is involved in the signaling system described in Fig. 11.07?

    <p>G protein-coupled receptor</p> Signup and view all the answers

    What is an example of a G protein-coupled receptor?

    <p>Adrenaline receptor</p> Signup and view all the answers

    What is the role of the ligand in the G protein-coupled receptor signaling system?

    <p>To bind to the receptor</p> Signup and view all the answers

    What is the primary mechanism by which G protein-coupled receptors trigger a cellular response?

    <p>Activation of the enzyme</p> Signup and view all the answers

    What is the result of the signaling system returning to the resting state?

    <p>The signaling system is turned off</p> Signup and view all the answers

    What is the primary function of ligand-gated ion channel receptors in the nervous system?

    <p>To open a channel, allowing ions to flow into or out of the cell</p> Signup and view all the answers

    What is the primary mechanism by which G protein-coupled receptors transmit signals?

    <p>By activating an enzyme that generates a second messenger</p> Signup and view all the answers

    What is the role of the G protein in the G protein-coupled receptor signaling pathway?

    <p>To activate an enzyme that generates a second messenger</p> Signup and view all the answers

    What is the primary function of enzyme-coupled receptors?

    <p>To activate an enzyme that generates a second messenger</p> Signup and view all the answers

    What is the primary characteristic of steroid receptors?

    <p>They bind to ligands in the nucleus</p> Signup and view all the answers

    What is the significance of the gate returning to the closed position in ligand-gated ion channel receptors?

    <p>It terminates the signal, allowing the cell to return to its resting state</p> Signup and view all the answers

    What is the result of the G protein binding to the receptor in the G protein-coupled receptor signaling pathway?

    <p>The G protein activates an enzyme that generates a second messenger</p> Signup and view all the answers

    What is the primary function of G protein-coupled receptors in humans?

    <p>To regulate a wide range of physiological processes, including sensation, movement, and hormone regulation</p> Signup and view all the answers

    What is the primary function of signal transduction in cellular signalling?

    <p>To relay signals from the receptor to affect cellular responses</p> Signup and view all the answers

    What is the term for the type of signalling that involves the release of signalling molecules from one cell and their binding to receptors on nearby cells?

    <p>Paracrine signalling</p> Signup and view all the answers

    What is the primary characteristic of long-distance signalling, also known as endocrine signalling?

    <p>Release of signalling molecules from one cell and binding to receptors on distant cells</p> Signup and view all the answers

    What is the term for the process by which a signalling molecule binds to a receptor and changes its shape?

    <p>Signal reception</p> Signup and view all the answers

    What type of signalling molecule is estrogen?

    <p>Lipid-soluble</p> Signup and view all the answers

    What is the primary function of receptor-ligand binding in cellular signalling?

    <p>To change the shape of the receptor protein</p> Signup and view all the answers

    What is the primary function of cell junctions in direct cell-to-cell signalling?

    <p>To allow direct communication between cells</p> Signup and view all the answers

    What is the term for the relay of molecules within the cell in response to a signal?

    <p>Signal transduction</p> Signup and view all the answers

    What is the primary function of receptors in signal transduction pathways?

    <p>To receive the signal</p> Signup and view all the answers

    What happens to the receptor when the ligand dissociates?

    <p>It becomes inactivated</p> Signup and view all the answers

    What is the role of GTP in signal transduction pathways?

    <p>To switch the G protein on</p> Signup and view all the answers

    What is the outcome of the signal transduction pathway described in the lecture?

    <p>Activation of glycogen phosphorylase</p> Signup and view all the answers

    What is the purpose of amplification in signal transduction pathways?

    <p>To amplify the signal</p> Signup and view all the answers

    What type of molecules can activate other proteins in signal transduction pathways?

    <p>Second messengers</p> Signup and view all the answers

    What is the common theme in signal transduction pathways?

    <p>Turning on and off the signal</p> Signup and view all the answers

    What is the outcome of signal transduction pathways?

    <p>Altered metabolism</p> Signup and view all the answers

    What is a possible outcome of signal transduction pathways involving growth factors?

    <p>Altered gene expression</p> Signup and view all the answers

    Which of the following is an example of a rapid signal transduction response?

    <p>Adrenaline</p> Signup and view all the answers

    What is a common outcome of signal transduction pathways involving actin-binding proteins?

    <p>Altered cell movement or shape</p> Signup and view all the answers

    What is a characteristic of signal transduction pathways involving steroid receptors?

    <p>Altered gene expression</p> Signup and view all the answers

    What is a common function of signal transduction pathways involving actin-binding proteins?

    <p>All of the above</p> Signup and view all the answers

    What is a characteristic of signal transduction pathways involving growth factors?

    <p>Altered gene expression</p> Signup and view all the answers

    Study Notes

    Meiosis

    • Meiosis has two consecutive divisions: meiosis I and meiosis II, with no DNA synthesis between them.
    • Genetic diversity in meiosis results from crossing-over during synapsis, independent assortment of chromosomes, and random fertilization.

    Meiosis I

    • In prophase I, chromosomes condense, spindles form, and the nuclear envelope breaks down.
    • A difference to mitosis: homologous chromosomes join together at regions called chiasmata, and crossing over occurs, where regions of homologous chromosomes are swapped.
    • In metaphase I, chromosomes align in the middle of the cell, with homologous chromosomes aligned together.
    • In anaphase I, chromosomes move to poles, and homologous chromosomes separate, while sister chromatids remain attached at the centromere.
    • In telophase I, two haploid cells form, each with paired sister chromatids.

    Meiosis II

    • Meiosis II is similar to mitosis, with the exception that four haploid cells are produced.

    Differences between Mitosis and Meiosis

    • Mitosis: one division, two diploid daughter cells, no crossing over, daughter cells genetically identical to parent cell.
    • Meiosis: two consecutive divisions, four haploid daughter cells, crossing over present, genetic diversity results.

    Cellular Biology and Biochemistry

    Organelles and Cell Division

    • Organelles: nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, Plastids are specialized organelles found in plant cells that are responsible for photosynthesis and other metabolic processes. They are present in green plants, algae, and some bacteria. According to their pigmentation and function, plastids can be categorized into several types, including:

      • Chloroplasts: responsible for photosynthesis and are found in green plants
      • Leucoplasts: involved in the synthesis of starch and other carbohydrates, found in etiolated plants
      • Chromoplasts: involved in the breakdown of chlorophyll and the synthesis of carotenoids, found in ripening fruits and flowers
      • Amyloplasts: involved in the synthesis of starch grains, found in potatoes and cereals
      • Elaeoplasts: involved in the synthesis of triglycerides, found in plants that store lipids

      Plastids have their own DNA, known as chloroplast DNA (cpDNA) or plastid DNA (ptDNA), which is inherited from the maternal parent. The genetic information encoded in cpDNA or ptDNA is responsible for the synthesis of proteins involved in photosynthesis and other metabolic processes.

      (including chloroplasts).

    • Cell division: mitosis (cellular growth) and meiosis (reproduction).

    Cell Junctions and Communication

    • Cell junctions: connections and communication between cells.
    • Connections: cells in multicellular organisms need to be stably attached to each other.
    • Communication: cells need to communicate and coordinate, through signalling molecules or direct cell-to-cell contact.

    Sex Chromosomes

    • In mammals: females = XX, males = XY.
    • In birds: females = ZW, males = ZZ.
    • In platypuses: females = XXXXXXXXXX, males = XXXXX/YYYYYY.

    Haploid and Diploid Cells

    • Haploid (n): one set of chromosomes.
    • Diploid (2n): two sets of chromosomes.
    • Examples: females = diploid, males = haploid in hymenoptera (bees, ants, etc.).

    Importance of Meiosis

    • Meiosis produces haploid gametes (sperm and eggs) in animals and haploid spores in plants.
    • These fuse to generate diploid offspring that grow through mitosis.

    Signal Reception

    • Receptors are specific for certain signals, ensuring only correct cells respond.
    • A ligand is a specific signaling molecule that binds to a specific receptor.

    Types of Receptors

    • Cell-surface receptors:
      • Ligand-gated ion channel receptors
      • G protein-coupled receptors
      • Enzyme-coupled receptors
    • Cytoplasmic receptors:
      • Steroid receptors

    Ligand-Gated Ion Channel Receptors

    • System involves: signal molecule (wide range possible), gated ion channel
    • When the signaling molecule binds, the channel opens, allowing specific ions to flow.
    • The gate must return to the closed position at the end of the signal.

    G Protein-Coupled Receptors (GPCRs)

    • Found associated with the plasma membrane in all eukaryotes.
    • 800 different GPCRs in humans, with 60% of drugs targeting GPCR pathways.
    • System involves: signal molecule (ligand), G protein-coupled receptor, G protein, enzyme.
    • G proteins are GTP-binding proteins that switch from inactive to active state upon ligand binding.

    G Protein-Coupled Receptors (GPCRs) - Activation

    • The signal molecule binds to the receptor, causing a shape change that allows the G protein to bind.
    • The G protein is activated by switching GDP for GTP.
    • Activated G protein then activates an enzyme, triggering a cellular response.

    G Protein-Coupled Receptors (GPCRs) - Deactivation

    • The signaling system is turned off and reset when the G protein is deactivated by hydrolysis of GTP to GDP.

    Examples of G Protein-Coupled Receptors

    • Adrenaline receptor
    • Rhodopsin: photoreceptor

    Cellular Signalling

    • Sometimes the cell that detects the signal is far from the responding cells.
    • The signal is relayed (transduced) as an electrical signal through the spine.

    Kinds of Cellular Signalling

    • Direct cell-to-cell signalling:
      • Cell junctions
      • Cell-cell recognition
    • Local signalling:
      • Paracrine signalling
      • Synaptic signalling
    • Long-distance signalling (endocrine signalling), mediated by hormones.

    Signalling Molecules

    • Can be gaseous, water-soluble, lipid-soluble, or proteins.
    • Examples: ethylene, estrogen, insulin.

    Reception - Transduction - Response

    • Signal reception involves a signaling molecule binding to a receptor, changing its shape.
    • Signal transduction involves the transmission of the signal.
    • Signal response involves a change in protein activity or expression.

    G Protein-Coupled Receptors (GPCRs)

    • G proteins are GTP-binding proteins that play a crucial role in signal transduction pathways.
    • The system involves a signal molecule (ligand) binding to the G-protein-coupled receptor, causing a shape change that allows the G protein to bind.
    • The G protein is activated by switching GDP for GTP.

    Signal Transduction Pathways

    • Signal transduction pathways can involve only proteins or proteins and second messengers.
    • Examples of signal transduction pathways include phosphorylation cascades.
    • The process involves signal reception, signal transduction, and signal response.

    Types of Receptors

    • Cell-surface receptors include ligand-gated ion channel receptors, G protein-coupled receptors, and enzyme-coupled receptors.
    • Cytoplasmic receptors include steroid receptors.
    • 30% of human proteins are cell surface receptors.

    Ligand-Gated Ion Channel Receptors

    • The system involves a signal molecule binding to the gated ion channel, opening it and allowing specific ions to flow.
    • It is crucial that the gate returns to the closed position at the end of the signal.
    • Examples include chemical synapses, where the ligand is a neurotransmitter (e.g., dopamine, acetylcholine) and the receptor is a transmitter-gated ion channel.

    G Protein-Coupled Receptors (GPCRs)

    • GPCRs are signal receptors found associated with the plasma membrane and are found in all eukaryotes.
    • There are 800 different GPCRs in humans, and 60% of drugs target GPCR pathways.

    Cellular Signalling

    • For any given cell, there are hundreds of different signals it can respond to, hundreds of different receptors, and thousands of different pathways that can be activated, leading to lots of different responses.
    • Signalling molecules can be gaseous, water-soluble, or lipid-soluble, and can be small molecules or proteins.
    • Long-distance signalling is also known as endocrine signalling, which is mediated by hormones.

    Signal Transduction

    • The process involves signal reception, signal transduction, and signal response.
    • A signalling molecule binds to a receptor, which changes shape, allowing the signal to be transduced and ultimately leading to a change in protein activity or expression.

    Cell Signalling

    • Signal transduction pathways involve three main themes: signal reception, signal transduction, and signal response.

    Signal Reception

    • Receptors are usually found in the plasma membrane.
    • Receptors change shape when a ligand binds.
    • Receptors can be switched off by ligand dissociation.

    Signal Transduction

    • Protein switches, such as GTP/GDP and phosphorylation/dephosphorylation, play a crucial role.
    • Small molecules, known as second messengers, activate other proteins.

    Signal Response

    • Effectors are responsible for the signal response.
    • Signal transduction pathways can have various outcomes, including:
      • Altered metabolism
      • Altered gene expression
      • Altered cell movement or shape

    Amplification

    • Amplification allows a small initial signal to be massively increased.
    • Example: 1 molecule of epinephrine can lead to 100 million molecules of glucose-1-phosphate.

    Common Theme

    • Turning on and off the signal is a common theme in signal transduction pathways.
    • Receptors, second messengers, and enzymes can all be turned on and off.

    Response Outcomes

    • Altered metabolism: involves changes in cellular metabolic processes.
    • Altered gene expression: involves changes in gene transcription, often involving growth factors and steroid receptors.
    • Altered cell movement or shape: involves changes in the cytoskeleton, and is involved in processes such as muscle contraction, wound healing, and embryo development.

    Response Timing

    • Extracellular signals can act slowly or rapidly, depending on the signal.
    • Examples: adrenaline (rapid) and growth factors (slow).

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    Description

    Learn about the stages of Meiosis I, including prophase and metaphase, and how it differs from mitosis. Understand the alignment of chromosomes and their attachment to kinetochores.

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