BLG 101 - Lecture 2

What is the structural and functional unit of life?

The cell.

What determines how well an entire organism functions?

The individual and combined activities of its cells.

Where do new cells come from according to cell theory?

Cells can arise only from other preexisting cells.

What are the three basic parts of a human cell?

1. Plasma membrane (flexible outer boundary), 2. Cytoplasm (intracellular fluid with organelles), 3. Nucleus (DNA-containing control center).

What is a generalized cell?

A concept representing the common structures and functions shared by all human cells.

What is the primary function of the plasma membrane?

It acts as an active barrier separating intracellular fluid (ICF) from extracellular fluid (ECF) and controls what enters and leaves the cell.

How do membrane proteins function in transport?

They form selective solute hydrophilic channels or hydrolyze ATP to actively pump solutes across the membrane.

How do membrane proteins function in signal transduction?

They act as receptors for chemical messengers (like hormones) through exposed binding sites. When bounded, the chemical messenger indulges in changing shape to trigger intracellular chemical reactions.

How do membrane proteins function in enzymatic activity?

They may act as enzymes with exposed active sites to substances in adjacent solutions, a team of enzymes are able to catalyze sequential steps of metabolic pathways in adjacent solutions.

How do membrane proteins function in cell-cell recognition?

Glycoproteins serve as identification tags that are specifically recognized by other cells.

How do membrane proteins attach to the cytoskeleton and ECM?

They anchor internal framework fibers and external matrix fibers to maintain cell shape, fix protein locations, and assist movement.

How do membrane proteins function in cell-to-cell joining?

They hook adjacent cells together in intercellular junctions or use CAMs to provide temporary binding sites for cell migration.

What are the three main types of cell junctions that bind cells together?

Tight junctions, Desmosomes, and Gap junctions.

Are all human cells bound to each other?

No, some cells (like blood cells and sperm cells) are unattached, but most bind together to form tissues and organs.

Two types of transport across cell membrane

1. passive

2. active (needs atp)

three types of passive

1. simple diffusion

2. facilitated diffusion

3. osmosis

denote that diffusion means high to low concentration (concentration gradient)

What is simple diffusion?

The process where nonpolar, lipid-soluble (hydrophobic) substances pass directly through the phospholipid bilayer without assistance.

What types of substances can pass through simple diffusion?

Nonpolar substances (oxygen, carbon dioxide, steroid hormones, fatty acids) and small amounts of very small polar substances like water.

Facilitated diffusion: carrier-mediated facilitated diffusion and channel-mediated facilitated diffusion

carrier: protein carrier that is specific for one chemical, as the solute nfs it changes the shape of the transport carrier

channel: mostly ions pass through channel proteins selected on basis of size and charge

What is osmosis?

The movement of water across a selectively permeable membrane, occurring when water concentration differs on two sides.

How does water cross the plasma membrane?

It diffuses directly through the lipid bilayer (due to its small size) or moves through specific channels called aquaporins (AQPs).

What is osmolarity?

A measure of the total concentration of solute particles in a solvent.

How does water concentration relate to solute concentration?

They are inversely related: as solute concentration increases, water concentration decreases because solute particles displace water.

In which direction does water move during osmosis?

From areas of low solute concentration (high water concentration) to areas of high solute concentration (low water concentration).

What is tonicity?

The ability of a solution to change a cell's shape or tone by altering its internal water volume.

What happens to a cell in an isotonic solution?

The solution has the same osmolarity as the cell, so cell volume remains unchanged.

What happens to a cell in a hypertonic solution?

Water flows out of the cell toward higher solute concentration, causing the cell to shrink (crenation).

What happens to a cell in a hypotonic solution?

Water flows into the cell toward higher solute concentration, causing the cell to swell and potentially burst (lysing).

What are the two major active membrane transport processes?

Active transport (primary and secondary) and vesicular transport.

Why are active membrane transport processes considered "active"?

They require ATP (cellular energy) directly or indirectly to transport substances.

What is active transport and what does it require?

It moves solutes against their concentration gradient (from low to high concentration), requiring ATP and carrier proteins (solute pumps).

What is the difference between antiporters and symporters?

Antiporters transport one substance into the cell while moving another out; symporters transport two different substances in the same direction.

What is the difference between primary and secondary active transport?

Primary active transport gets energy directly from ATP hydrolysis, while secondary active transport gets energy indirectly from ionic gradients (like Na+) created by primary active transport.

What is vesicular transport?

The movement of large particles, macromolecules, and fluids across the membrane inside membranous sacs called vesicles, requiring ATP.

What are the main types of vesicular transport processes?

Endocytosis (transport into cell via phagocytosis, pinocytosis, or receptor-mediated endocytosis), Exocytosis (transport out of cell), and Vesicular trafficking (transport between intracellular areas/organelles).

What is phagocytosis

• engulf particle by formulation of pseudopod and closing around it (phagosome) which combines with lysosome and is digested

• receptors can bind to microorganisms

what is pinocytosis

the gulping of ecf w/ solutes into tiny vesicles (non specific)

what is receptor mediated endocytosis

ec substances bind to specific receptors allowing for ingestion in protein coated vesicles

how does exocytosis work

1. membrane bound organelle moves to plasma membrane

2. vsnares (vesicle proteins) bind w tsnares (membrane proteins)

3. vesicle and plasma fuse

4. contents vesicle excreted

What is cytoplasm and what are its two main components?

The cellular material between the plasma membrane and nucleus, composed of cytosol (gel-like fluid with water/solutes) and organelles (specialized functional structures).

What is the difference between cytosol and organelles?

Cytosol is the gel-like fluid containing dissolved molecules, while organelles are the metabolic machinery structures with specialized functions.

Why are mitochondria called the "power plant" of the cell?

They produce most of the cell's ATP energy through aerobic cellular respiration.

What are the structural features of mitochondria?

They have a double membrane with inner folds called cristae, contain their own DNA/RNA/ribosomes, and resemble bacteria.

What is so special about cristae

embedded with membrane proteins playing a role in cellular respiration

What are the main functions of the Rough Endoplasmic Reticulum (Rough ER)?

It synthesizes proteins for secretion, creates membrane proteins and phospholipids, and modifies proteins(enter through cisterns and are modified as they go thru fluid filled tube) before sending them to the Golgi apparatus in vesicles.

What are the main functions of the Smooth Endoplasmic Reticulum (Smooth ER)?

It carries out lipid/cholesterol/steroid synthesis, converts glycogen to glucose, and stores and releases calcium.

What is the primary function of the Golgi apparatus?

It modifies, concentrates, and packages proteins and lipids received from the rough ER.

What are the three steps involved in Golgi apparatus processing?

1. Vesicles from ER fuse with the cis face, 2. Contents are modified, tagged, sorted, and packaged inside, 3. Final products pinch off the trans face in new vesicles directed to their destination.

What type of sacs are the Golgi made of

membraneous cistern sacs

What is the main function of peroxisomes?

They are membranous sacs containing enzymes (oxidase and catalase) that neutralize toxic free radicals produced during metabolism.

How do peroxisomal enzymes detoxify harmful molecules?

Oxidase converts free radicals to toxic hydrogen peroxide (H2O2), which catalase then rapidly converts into harmless water.

What are lysosomes and why are they considered "safe" sites?

They are spherical membranous bags containing digestive enzymes (acid hydrolases); they isolate harmful intracellular digestion from the rest of the cell.

What are the primary functions of lysosomes?

They digest ingested bacteria, viruses, and toxins, degrade nonfunctional organelles, and break down glycogen to release glucose.

What causes lysosomal storage diseases?

Mutations in one or more lysosomal digestive enzymes that prevent them from functioning properly.

What is Tay-Sachs disease and how does it affect cells?

A condition where a patient lacks a specific lysosomal enzyme needed to break down glycolipids, causing glycolipids to build up in brain cells and disrupt nervous system function.

What are ribosomes and what are they made of?

Nonmembranous organelles that serve as the site of protein synthesis, composed of protein and ribosomal RNA (rRNA).

What is the functional difference between free and membrane-bound ribosomes?

Free ribosomes synthesize soluble proteins that function in cytosol/organelles; membrane-bound ribosomes (on ER) synthesize proteins for membranes, lysosomes, or secretion.

What is the cytoskeleton and its main function?

An elaborate network of protein rods throughout the cytosol that acts as the cell's "bones, ligaments, and muscle" to support structure and facilitate movement of cellular components.

cytoskeleton - microfilaments

strands made of spherical protein subunits called actin

• smallest

cytoskeleton - intermediate filaments

tough, insoluble protein fibres constructed like woven ropes and composed of tetrameter (4 ) fibris

microtubules - cytoskeleton

tubulin subunits hollow tubes of spherical protein

What is a centrosome and what are centrioles?

The centrosome is a microtubule organizing center that contains a pair of barrel-shaped centrioles positioned at right angles to each other.

What is the role of centrioles during cell division and surface structures?

Centrioles organize assembled microtubules that radiate outward to form the mitotic spindle apparatus during division, and they form the structural basis of cilia and flagella.

What primary function does the nucleus serve in a cell?

It contains the genetic blueprints (DNA) for synthesizing nearly all cellular proteins and responds to signals controlling protein production.

How do cells differ in their number of nuclei?

Most cells are uninucleate (one nucleus), some are multinucleate (skeletal muscle, bone, liver cells), and red blood cells are anucleate (no nucleus).

What are the three main structural components of the nucleus?

The nuclear envelope, nucleoli, and DNA (present as chromatin or chromosomes).

What is the function of nucleoli within the nucleus?

They are dark-staining spherical bodies involved in synthesizing ribosomal RNA (rRNA) and assembling ribosome subunits.

What is chromatin composed of?

30% threadlike DNA, 60% histone proteins, and 10% RNA.

What is a nucleosome and what role do histones play?

A nucleosome is a fundamental unit of chromatin consisting of DNA wrapped around histone proteins, which help regulate gene expression.

What is a chromosome?

A condensed form of chromatin structure.

Why does chromatin condense into chromosomes during cell division?

The condensed structure protects fragile chromatin threads from damage while being moved during cell division.

What is the cell cycle?

The series of developmental changes a cell undergoes from the time it is formed until it reproduces.

What are the two major periods of the cell cycle?

Interphase (where the cell grows and carries out routine functions) and Cell Division / Mitotic Phase (where the cell divides into two).

What is the S phase of Interphase and how does DNA unzipping begin?

S phase is when DNA replicates; DNA strands unwind and unzip at a replication fork within an active replication bubble.

What are the roles of RNA primers, DNA polymerase, and DNA ligase in DNA replication?

An RNA primer initiates replication, DNA polymerase attaches to add nucleotides along template strands, and DNA ligase splices discontinuous segments on the lagging strand.

Why do cells divide and which tissues lack efficient cell division?

Most cells replicate continuously for growth and repair, but skeletal, cardiac, and nerve cells divide poorly and replace damaged tissue with scar tissue.

What are the two distinct events of the M (mitotic) phase?

Mitosis (nuclear division) and Cytokinesis (division of the cytoplasm).

What is mitosis?

The process of nuclear division in M phase where duplicated DNA is accurately distributed into two new daughter cell nuclei.

What are the main "Go" signals that stimulate cell division?

A critical surface-to-volume ratio (membrane area becomes inadequate for cell volume) and chemical messengers like growth factors and hormones.

What is contact inhibition in the context of cell division?

A "Stop" signal where normal cells cease dividing once they come into direct contact with surrounding cells due to lack of available space.

How do Cyclins and Cdks regulate the cell cycle?

Cyclins accumulate during interphase and bind to Cdks (Cyclin-dependent kinases), forming Cyclin-Cdk complexes that trigger enzyme cascades preparing the cell for division before cyclins are destroyed.

What are cell cycle checkpoints and what happens at the G1 checkpoint?

Checkpoints are regulatory events that halt division if processes are faulty; the G1 checkpoint (restriction point) is the most critical—if a cell fails it, it enters non-dividing G0 phase.

What is a gene and how does it code for proteins?

A gene is a segment of DNA holding the code for a specific polypeptide, where sequential three-base nitrogenous sequences (triplet code) dictate specific amino acids.

What is the structural difference between exons and introns?

Exons are the coding regions of a gene that specify amino acids, while introns are noncoding intervening sequences.

What are the three main types of RNA and their primary functions?

mRNA carries copied DNA code via transcription, rRNA forms the structural backbone of ribosomes, and tRNA transports specific amino acids to the ribosome via anticodon-codon pairing during translation.

What are the two major steps of protein synthesis?

Transcription (where DNA information is coded into mRNA) and Translation (where mRNA is decoded to assemble polypeptides).

What are the three phases of transcription and what occurs during each?

1) Initiation: RNA polymerase separates DNA strands. 2) Elongation: RNA polymerase adds complementary nucleotides to the growing mRNA strand (forming a short DNA-RNA hybrid). 3) Termination: transcription stops when RNA polymerase hits a termination signal code.

What is an aminoacyl-tRNA and how does tRNA select its specific amino acid?

An aminoacyl-tRNA is a tRNA molecule loaded with its specific amino acid at its stem region, which is determined by the specific triplet anticodon located at the opposite end of the tRNA.

How does initiation of translation occur?

The small ribosomal subunit and initiator tRNA bind mRNA at the start codon; the large subunit then attaches, placing the initiator tRNA in the P site with A and E sites empty.

What are the three sub-steps of translation elongation?

1) Codon recognition: incoming tRNA binds the codon in the A site. 2) Peptide bond formation: polypeptide chain is transferred from P site tRNA to A site tRNA. 3) Translocation: ribosome shifts 3 bases down mRNA, moving tRNAs from A to P and P to E (where it is ejected), leaving the A site open.

What triggers termination during translation and what are the three stop codons?

Translation ends when any of the three stop codons—UGA, UAA, or UAG—enters the A site of the ribosome.

What is the role of the ER signal sequence and SRP in protein processing?

The ER signal sequence on a growing polypeptide binds to a Signal-Recognition Particle (SRP), directing the ribosome to dock on the rough ER surface.

What happens to a newly synthesized protein inside the Rough ER?

The polypeptide enters the rough ER lumen for processing and is subsequently enclosed in a transport vesicle targeted for the Golgi apparatus.

How is genetic information transferred from DNA to an amino acid sequence?

DNA triplets are transcribed into mRNA codons, which then base-pair with complementary tRNA anticodons to assemble the correct amino acid sequence.

How does a tRNA anticodon sequence relate to the original DNA sequence?

The tRNA anticodon sequence is identical to the DNA template sequence, except uracil (U) replaces thymine (T).