Biology 151 Exam 3

Meiosis

Cell division that produces reproductive cells (gametes)

• Sperm & egg

• Daughter cells are genetically different from parent cells

  • Genetic material is halved

Gamete

A sex cell (sperm or egg)

Mitosis

Cell division that produces body cells (somatic cells)

Cytokinesis

The division of the cytoplasm into two daughter cells

• Occurs in mitosis and meiosis

• Occurs during Telokinesis

• Cleavage furrow in animal cells

• Cell plate in plant cells

Chromosome

A single long double helix of DNA wrapped around histone proteins

Gene

A particular region of DNA in a chromosome

• Codes for specific RNA / proteins

Sister chromatids

Identical copies of a duplicated chromosome, attached by a centromere

• Seperated during Anaphase

  • Each half goes to a daughter cell

Cell cycle phases

The cell alternates between Interphase and M Phase

1. G₀ phase - Not dividing

2. Interphase - Preparation to divide

   1. G₁ phase - Cell grows and duplicates organelles

   2. S phase - Cell duplicates chromosomes and centrosome

   3. G₂ phase - Cell grows more and reorganizes its organelles

3. M phase - Division

   1. Mitosis - Replicated chromosomes are separated by centrosomes

      • Forms two daughter nuclei

   2. Cytokinesis - The cytoplasm divides

      • Forms two daughter cells

Interphase

The cell prepares to divide

1. G₁ phase - Cell grows and duplicates organelles

2. S phase - Cell duplicates chromosomes and centrosome

3. G₂ phase - Cell grows more and reorganizes its organelles

Centrosome

A microtubule structure that helps separate sister chromatids in anaphase

Mitotic (M) Phase

The cell is dividing

1. Mitosis - Replicated chromosomes are separated by centrosomes

   • Forms two daughter nuclei

     1. Prophase - Chromosomes condense, miotic spindle forms, nucleolus breaks down

     2. Prometaphase - Miotic spindle captures & organizes chromosomes

     3. Metaphase - Miotic spindle lines chromosomes in the middle of the cytoplasm

     4. Anaphase - Sister chromatids are seperated and pulled to opposite poles

     5. Telophase - The cell restablishes its structures

2. Cytokinesis - The cytoplasm divides

   • Forms two daughter cells

     • Occurs during Telophase

Prophase

Mitosis - Step 1

• Chromosomes condense

• Miotic spindle forms

• Nucleolus breaks down

Miotic spindle

A microtubule structure that organizes and moves chromosomes during mitosis

• Grows between centrosomes

• Formed during prophase

Nucleolus

The region of the nucleus where ribosomes are made

• Broken down during Prophase

Prometaphase

Mitosis - Step 2

• Chromosomes condense more

• Nuclear envelope breaks down, chromosomes are released

• Miotic spindle grows and captures chromosomes

Kinetochore

A patch of proteins at the centrosome of each sister chromatid where miotic spindle grabs

Metaphase

Mitosis - Step 3

• Miotic spindle line chromosomes up at the metaphase plate (middle of cell)

• Spindle Checkpoint - Ensures that everything is attached correctly. The cell will not move on the the next phase if not

Spindle checkpoint

• Occurs during metaphase

• The cell checks that:

  • Chromosomes are correctly lined up

  • Each chromosome has two correctly attached kinetochores

  • All kinetochores are correcly attached to the miotic spindle

• Division will halt if the checkpoint is failed

Anaphase

Mitosis - Step 4

• Sister chromatids separate into individual chromosomes

• Each new chromosome is pulled to opposite ends of the cell

Telophase

Mitosis - Step 5

• Mitotic spindle breaks down

• Two new nuclei form

• Chromosomes decondense

• Simultaneously, cytokinesis occurs

Cleavage furrow

Cytokinesis in animal cells

• Actin filaments pinch across the cytoplasm to split the cell into two

Cell plate

Cytokinesis in plant cells

• A new cell wall forms down the middle of the cell, splitting it into two

Binary fission

Cell division and reproduction in bacteria

1. DNA is copied and protein filaments attach to either pole of the cell

2. DNA copies separate, a protein ring forms in the middle of the cell

3. The cell membrane is cleaved by the protein ring

Cyclin-CDK complex

Protein complexes that push the cell towards the next phase when activated

• Often requires an activating kinase to phosphorylate the complex

Cyclin-dependent kinase (CDK)

A kinase that binds to cyclin to produce a protein complex that pushes the cell towards the next phase

Cyclin

A protein that binds to CDK to produce a protein complex that pushes the cell towards the next phase

• Concentrations cycle through the cell cycle

• Specific to the phase transition

Kinase

Proteins that add phosphate groups to molecules (phosphorylate)

M-Phase promoting factor (MPF)

A cyclin-CDK complex that pushes the cell into M-phase

• Inhibited by phosphorylation

Cell cycle checkpoints

Regulatory points throughout the cell cycle in which the cell decides whether to proceed with division

Cancer is caused by checkpoint failures

Tumor

A growth caused by cells that divide without regulatory control at checkpoints

M-phase checkpoint

Checkpoint conditions

• Sister chromatids have attached to the mitotic spindle

• Chromosomes have properly seperated

• M-phase promoting factor is absent

G₁ checkpoint

Checkpoint conditions

• Cell size is adequate

• Nutrients are sufficient

• Social signals are present

• DNA is not damaged

G₂ checkpoint

Checkpoint conditions

• Chromosomes have successfully replicated

• DNA is not damaged

• M-phase promoting factor (MPF) is present and active

p53

A regulatory protein that stops the cell cycle if DNA is damaged

• The protein binds to the DNA, which produces a cyclin-CDK inhibitor

Oncogenes

Overexpressed genes that promote constant cell division

Benign tumor

A noncancerous and noninvasive tumor

Malignant tumor

A cancerous and invasive tumor

• Spreads through the body and creates more tumors

E2F

A protein that triggers the expression of genes required for S phase

• Deactivated by Rb protein

Rb

A tumor suppressor that binds to E2F to deactivate it and inhibit the cell from moving into S phase

Causes of cancer

1. Permanently activated CDK

   • The cell is constantly dividing

2. Defective Rb

   • Cannot bind to E2F, so S phase is falsely started

3. Mutated p53

   • Cannot halt division if DNA is damaged

Membrane proteins

Proteins that regulate transport across the plasma membrane

• Attach to interior cytoskeletal structures and exterior matrix structures

The extracellular matrix (ECM)

A protective layer or wall that forms just beyond the plasma membrane

• Defines cell shape

• Attaches cells to other cells (junctions)

• First defense system

Components

• Collagen fibrils

• Proteoglycans

• Integrin proteins

• Cytoskeleton microfilaments

Plant extracellular matrix

Primary cell wall - Located to the very exterior of the cell

Secondary cell wall - Located between the primary cell wall and the plasma membrane

• Contains waxes in leafs

• Contains lignin in wood

Pectin

A gelatinous sugar embedded between cellulose microfibrils in the primary cell wall that store moisture

Collagen

The most abundant structural protein in the animal extracellular matrix

• Form fibrils that provide support and flexibility

Proteoglycans

The gelatinous ground substance of the extracellular matrix

• Composed of many polysaccharides attached to a core protein

• Give cartilage its rubbery consistency

• Stores water

Tissue

Similar cells that function as a unit

• More ECM than actual cells

Integrins

Membrane proteins that bind to cross-linking proteins in the extracellular matrix

• Laminins - Anchors the ECM to the plasma membrane and cytoskeleton

Laminins

A type of integrin (transmembrane protein) that anchors the ECM to the plasma membrane and cytoskeleton

Cell-cell attachments

Materials and structures that allow cells to connect, communicate, and transfer materials

1. Middle lamella - Glues plant cells together

2. Tight junctions - Stitch animal cells together via proteins

3. Desosomes - Anchor cells together via cytoskeleton intermediate filaments

4. Gap junctions - Attach animal cells with gaps for small molecule transfer

5. Plasmodesmata - Attach plant cells with gaps for small molecules transfer

Epithelia

The tissues that line organs

• Require very strong cell-cell attachments

Middle lamella

An indirect cell-cell attachment that glues plant cells together

• Made of gelatinous pectins

• Continuous with the primary cell wall

Tight junction

A cell-cell attachment ta stitches animal cells together

• Watertight seal

• Chains of proteins line up and bind to each other

• Usually found in epithelia (Organ-lining cells)

• Can loosen to permit transport or in response to environmental changes

Desosomes

Strong cell-cell attachments common in animal epithelial and muscle cells

• Intermediate filaments inside of the cell link to cadherin proteins

  • Cadherins extend across the ECM and bind to the cadherins of adjacent cells

    • Cadherins only bind to cadherins of the same type

Gap junctions

Cell-cell attachments in animal cells that allow ions and small molecules to flow between cells

• Communication portals - Channels that help adjacent cells coordinate activities

Plasmodesmata

Cell-cell attachments in plant cells that allow ions and small molecules to flow between cells

• Symplast - A continuous network of cytoplasm

• Apoplast - A continuous network of cells walls and ECMs

  • Filters water and nutrients before they enter the cell

Signaling molecules

Molecules that deliver messages between cells by binding to receptor proteins

• Lipid-insoluble - Hydrophilic, do not cross the plasma membrane

  • Processed by signal transduction

• Lipid-soluble - Hydrophobic, diffuse across the plasma membrane

  • Processed directly in the cells cytoplasm

Receptor proteins

Membrane proteins that change shape and activity after binding to a signaling molecule

Hormones

Information-carrying signaling molecules

• Often trigger changes in gene expression

• Secreted from cells

• Circulate the body

• Act on target cells far away

Signal transduction

The conversion of an extracellular hormone into an intracellular signal

• Required for hydrophilic, lipid-insoluble signaling molecules

Steps

1. Signal reception - The signaling molecule binds to a receptor protein outside of the plasma membrane

2. Signal transduction - The extracellular signal is converted into an intracellular signal

   • The signal may be amplified

3. Signal response - The signal may lead to changes in protein activity or gene expression

Direct signal processing

A signal diffuses across the plasma membrane and is processed by receptors in the cytoplasm

• Used for hydrophobic, lipid-soluble signaling molecules

Steps

1. Signal arrival - A carrier protein transports the hormone to the cell surface

2. Signal entry - The hormone diffuses across the plasma membrane into the cytosol

3. Signal reception - The hormone binds to a receptor protein, inducing conformational change

4. Direct signal response - The hormone receptor complex binds to the DNA, inducing an change in gene expression

G-protein-coupled receptors (GPCRs)

Receptor proteins that initiate the production of second messengers inside the cell

• Required for hydrophilic, lipid-insoluble signals that cannot cross the plasma membrane

• Amplify and diversify the signal

• Active when bound to GTP

• Inactive when bound to GDP

Second messengers

Amplified signals triggered by an activated G-protein-coupled receptor (GPCR)

• Diffuse rapidly throughout the cell

• Produced quickly in large quantities

• May activate protein kinases, which can activate / inactivate other proteins

Protein kinases

Proteins that activate or deactivate other proteins by phosphorylating them (adding phosphate groups)

Enzyme-linked receptors

Transmembrane signal receptors that phosphorylate proteins inside of the target cell

• Directly catalyze intracellular reactions

• Receptor tyrosine kinases (RTKs) - The best known group of this receptor

Receptor tyrosine kinases (RTKs)

Enzyme-linked receptors that autophosphorylate (phosphorylate themselves

• Signal transduction steps

  1. A hormone binds to 2 RTK subunits, they form a dimer

  2. RTK uses ATP to autophosphorylate

  3. Proteins build a bridge between RTK and Ras protein

     • Activates Ras

  4. Activated Ras phosphorylates protein kinase

  5. Triggers a phosphorylation cascade of protein kinases

Mitogen-activated protein kinases (MAPKs)

Signaling molecules that activate cell division by phosphorylating proteins

Phosphatases

Proteins that remove phosphate groups from proteins

• Regulate signaling pathways

• Opposite of kinases

Crosstalk

Signaling pathways interact to form a complex signaling network

• Pathways can inhibit and stimulate each other

Quorum sensing

Unicellular signaling pathways that respond to population density

• Allows bacteria to coordinate activities

• Can occur through G-protein coupled receptors (GPCRs)

• May cause free-living cells to aggregate (form a collective body)

Adenylyl cyclase

A membrane-bound enzyme that amplifies signals

• Converts ATP into cAMP (a second messenger)

• Triggered by G-protein coupled receptors

Photosystems

Proteins complexes of chloroyphyll and accessory pigments in the thylakoid membrane

• Exterior - Light-harvesting complex

• Interior - Reaction center

Photosystem reaction center

Where electromagnetic energy from sunlight is transformed into chemical energy