Anatomy & Physiology I: Chapter 3

Cell Structure, Function, and Processes

What is a cell?

The structural and functional unit of all life.

What are the three classes of extracellular materials?

1. Extracellular fluids (blood plasma, interstitial fluid, Cerebrospinal fluid), 2. Cellular secretions ( saliva, mucus & gastric juices), 3. Extracellular matrix (e.g., collagen, elastin).

What are the three major regions of a generic cell?

1. Nucleus (control center), 2. Cytoplasm (site of metabolic processes), 3. Plasma membrane (barrier and communication).

What are four important components of the plasma membrane?

1. Phospholipids (form the bilayer), 2. Cholesterol (stabilizes membrane fluidity), 3. Integral proteins (transport and communication), 4. Peripheral proteins (enzymatic functions and signaling).

What are the functions of membrane proteins?

1. Transport, 2. Enzymatic activity, 3. Signal transduction, 4. Cell-cell recognition, 5. Intercellular joining, 6. Attachment to the cytoskeleton and extracellular matrix.

What are tight junctions?

They prevent leakage between cells

What are desmosomes?

They stop the cells from tearing apart (stability)

What are gap junctions?

They allow ions & small molecules to pass between cells for rapid communication

What is the defining difference between active transport and passive transport?

Active transport requires energy (ATP) to move substances against their concentration gradient, while passive transport does not.

What is passive transport?

Doesn’t require energy (ATP); it moves molecules down their concentration gradient

What are the 3 types of passive transport?

Simple diffusion, facilitated diffusion, & osmosis

What is simple diffusion?

The movement of lipid-soluble molecules down their concentration gradient from high to low, without energy

What is facilitated diffusion?

The process of transporting molecules across the plasma membrane via protein channels or carriers, such as glucose and ions.

What is osmosis?

The movement of water across a selectively permeable membrane from areas of low osmolarity to areas of high osmolarity

What are the 2 types of active transport?

Active transport & vesicular transport

What is active transport?

The process requires energy (ATP). Carrier proteins (pumps) move solutes (ions & molecules) across a cell membrane against their concentration gradient.

What is vesicular transport?

The transport of large particles & fluids through vesicles. This process requires energy (ATP)

What are specialized water channels that speed up osmosis?

Aquaporins

What is osmolarity?

The measure of solute concentration in a solution

What happens to a cell in a hypertonic solution?

The solute concentration outside the cell is higher, causing water to move out of the cell

What happens to a cell in an isotonic solution?

The solute concentration is equal inside and outside the cell, resulting in no net movement of water

What happens to a cell in a hypotonic solution?

The solute concentration outside the cell is lower, causing water to move into the cell

What is endocytosis?

The process of taking substances into the cell

What are the 3 types of endocytosis?

Phagocytosis, pinocytosis, & receptor-mediated endocytosis

What is phagocytosis?

Endocytosis of large molecules or microorganisms

What is pinocytosis?

Endocytosis of fluids with small solutes

What is receptor-mediated endocytosis?

Specific substances use specific receptors

What is exocytosis?

The process of expelling substances from the cell

What are the 4 steps of exocytosis?

1. The vesicle travels to the plasma membrane. 2. The vesicle fuses with the plasma membrane. 3. The pores open. 4. The vesicle contents are released into the extracellular space

What is the function of mitochondria?

The powerhouses of the cell, producing ATP through cellular respiration

What is the function of the rough endoplasmic reticulum (RER)?

It’s involved in the synthesis and processing of proteins destined for secretion or for use in the cell membrane.

What is the function of Smooth endoplasmic reticulum (SER)?

It stores calcium, detoxifies harmful substances, and metabolizes lipids & glucose

What is the function of lysosomes?

They contain enzymes that break down waste materials and cellular debris that’s brought in during endocytosis

What are the three filament types of the cytoskeleton?

Microfilaments, Intermediate filaments, & Microtubules

What are microfilaments?

They are made of actin protein, support cell shape, & form a cleavage furrow that divides 1 cell into 2. Responsible for changes needed for endocytosis & exocytosis

What are intermediate filaments?

They are strong, stable, rope-like protein fibers that attach to desmosomes to help a cell resist external forces. They maintain the shape of the nucleus

What are microtubules?

They are made of tubulin protein & determine the cell shape, organelle distribution, form the mitotic spindle for cell division, & form cilia & flagella in aid of cell movement

What are cilia?

Short, hair-like structures on a cell surface that help the cell move in a coordinated back-and-forth motion like oars.

What are flagella?

Longer hair-like structure that propels the cell itself in a propeller like motion

What is the function of the centrosome?

It organizes microtubules and is critical for cell division.

What is the function of the nucleolus?

It’s responsible for producing ribosomal RNA (rRNA) and assembling ribosomes.

What is the cell cycle?

The changes a cell goes through from the time it’s formed until it reproduces

What are the phases of the cell cycle?

1. Interphase (G1, S, G2) and 2. Mitotic phase (Mitosis and Cytokinesis).

What is interphase and its 3 sub-phases?

______ is the period where growth & regular activities occur. Gap 1 (G1), synthesis (S) & Gap 2 (G2)

What occurs during Gap 1 (G1)?

Growth & metabolism. Cells that permanently stop dividing enter G0

What occurs during synthesis (S)?

DNA replication

What occurs during Gap 2 (G2)?

Preparation for cell division.

What state is DNA in during interphase

DNA is in an uncondensed chromatin state during interphase

What is semiconservative replication?

The process of DNA replication where each new DNA molecule consists of one old strand and one new strand. 3 steps occur: Uncoling & separation, assembly, & restoration

What occurs during uncoiling in semiconservative replication?

Helicase unwinds DNA

What occurs during assembly in semiconservative replication?

DNA polymerase adds nucleotides to each DNA template to form new strands

What occurs during restoration in semiconservative replication?

Ligase glues any broken bits of new chromosome

What is the M phase (mitotic phase)?

The period during which cell division of the nucleus & cytoplasm occurs. There are 2 phases: Mitosis & cytokinesis

What is mitosis?

The division of chromosomes between two daughter cells. There are 4 stages: Prophase, metaphase, anaphase, & telophase

What occurs during prophase?

Chromatin condenses & chromosomes are formed. Each chromosome & sister chromatid are held by a centromere. Centrosomes separate & migrate to opposite poles of the cell. The mitotic spindle forms & the nuclear envelope breaks up

What occurs during metaphase?

Centromeres of chromosomes align on the mitotic spindle at the equator of the cell, midway between the poles, called the metaphase plate

What occurs during anaphase?

Centromeres of chromosomes split, each sister chromatid becomes a separate chromosome, and are pulled to one of the 2 poles of the cell

What occurs during telophase?

Chromosomes decondense to form chromatin. A new nuclear envelope forms around the chromatin. The mitotic spindle disappears

What occurs during cytokinesis?

It begins during late anaphase (part of M-phase but not mitosis). The microfilament ring contracts to form a cleavage furrow. Two daughter cells are pinched apart. Each will contain a nucleus with a complete set of DNA & cytoplasm

What are the cell cycle checkpoints?

G1 checkpoint, G2 (M checkpoint)

What occurs during the G1 checkpoint?

It’s known as a restriction point and acts like a gate. It only opens if cell growth is sufficient

What occurs during the G2 checkpoint?

The gate opens if DNA replication is complete & without major errors

What is the role of mRNA in protein synthesis?

It carries the genetic information from DNA to the ribosome for protein synthesis.

What is the role of tRNA in protein synthesis?

It transports specific amino acids to the ribosome during translation.

Where does transcription occur in the cell?

It occurs in the nucleus. It’s the process of creating mRNA from a DNA template.

Where does translation occur in the cell?

It occurs in the cytoplasm at the ribosome. It’s the process of mRNA being read and created into specific proteins.

What is gene expression?

The process by which a cell uses the information in a gene to create a functional product, such as a protein or functional RNA

What is DNA in gene expression?

A Blueprint that holds code for protein synthesis. Genes are segments of DNA that code for a Polypeptide. The genetic code is created by triplets of nucleotides.

What is mRNA in gene expression?

It’s a go-between molecule linking DNA to protein. mRNA is processed and exported from the nucleus. mRNA serves as a template for protein translation.

What is gene expression of a protein?

Protein enzymes do most of the cells’ work. The cytoskeleton is built from proteins. Ribosomes translate amino acid chains from MRNA.