Cell Biology, Tissues, and Molecular Genetics Review

Comprehensive Q&A flashcards covering cell structure, organelles, membrane transport, tissue types and histology, eukaryotic gene expression, transcription, translation, DNA replication, and cell cycle regulation.

What are the nine primary cell shapes described in the lecture notes?

Squamous, polygonal, discoidal, cuboidal, stellate, fusiform, columnar, spheroidal, and fibrous.

What limits cell size, and what specific ratio affects this process?

Cell size is limited by the diffusion of nutrients and waste products, which is affected by the surface area to volume ratio.

What are the main structural components of the plasma membrane?

Phospholipid bilayer, glycolipids, transmembrane proteins, glycoproteins, peripheral proteins, protein channels, cholesterol, and cytoskeleton filaments.

What sequence of events occurs during second messenger signaling in a cell?

First messenger binds receptor -> Receptor relays signal to G Protein (uses GTP) -> G Protein relays signal to effector enzyme (e.g., adenylate cyclase) -> Effector enzyme activates second messengers (e.g., ATP to cAMP) -> Second messenger activates cytoplasmic kinases -> Kinases activate other enzymes.

What are microvilli, what size are they, and what is their primary function?

Microvilli are 1\text{ to }2\thinspace\text{̢m} membrane extensions that form a brush border to increase surface area for absorption.

How do nonmotile primary cilia differ from motile cilia in function and location?

Cilia are 7\text{ to }10\thinspace\text{̢m} long hair-like processes. Nonmotile primary cilia serve sensory functions (e.g., in the nose and inner ear), whereas motile cilia beat in waves to propel materials such as mucus in the respiratory tract or an egg cell in the uterine tubes.

How do the structures and functions of rough ER and smooth ER differ?

Rough ER consists of cisternae covered with ribosomes and functions in protein synthesis and membrane production. Smooth ER has more tubular, branched cisternae and functions in lipid synthesis, detoxification, and calcium storage.

What roles does the Golgi complex perform in the cell?

It synthesizes carbohydrates, processes proteins received from the rough ER, and packages them into Golgi vesicles that may become lysosomes, fuse with the plasma membrane, or form secretory vesicles for stored product release.

How is the mitochondrion structured to perform ATP synthesis?

It is surrounded by a double membrane with the inner membrane folded into cristae, where ATP-synthesizing enzymes are located. The space between cristae is the intermembrane space.

What are the three primary embryonic germ layers and which tissue types derive from each?

Ectoderm (outer) forms the epidermis and nervous system; Mesoderm (middle) forms cardiac muscle, bone, and blood; Endoderm (inner) forms mucous membranes and digestive glands.

What are the four main tissue classes and their basic functions?

Epithelial (covers organ surfaces and forms glands; protection, secretion, absorption), Connective (more matrix than cells; supports, protects, and binds tissues together), Nervous (rapid signal transmission), and Muscular (contraction and movement).

What defines simple epithelia, and what are its three primary cell shapes?

Simple epithelia consist of a single layer of cells where every cell touches the basement membrane. Its three main shapes are simple squamous, simple cuboidal, and simple columnar.

What structural feature defines pseudostratified epithelia?

All cells touch the basement membrane, but not all cells reach the apical surface.

Where is urothelium located, and what is its special functional property?

Urothelium (transitional epithelium) is unique to the urinary tract and allows the epithelium to stretch and relax.

What tissue examples correspond to simple squamous, simple cuboidal, simple columnar, and pseudostratified columnar epithelia?

Simple squamous is found in the lungs, simple cuboidal in the kidney, simple columnar in the stomach, and pseudostratified columnar in the trachea.

What are the three fiber types found in fibrous connective tissue and their characteristics?

Collagenous fibers (tough, flexible, resistant to stretch; in tendons, ligaments, dermis), Reticular fibers (thin collagen coated with glycoprotein, forming mesh frameworks in spleen and lymph nodes), and Elastic fibers (coiled elastin coated with glycoprotein that stretch and recoil in skin, lungs, and arteries).

How do areolar tissue and reticular tissue differ in structure and function?

Areolar tissue features a loose arrangement of collagen and elastin fibers with blood vessels that binds epithelia to deeper tissues. Reticular tissue consists of a loose network of reticular fibers infiltrated with leukocytes, providing a supportive framework for lymphoid organs.

How do dense regular and dense irregular connective tissues differ?

Dense regular tissue has parallel, wavy collagen fibers that connect bone to bone or muscle to bone to resist physical stress. Dense irregular tissue has randomly oriented collagen fibers to withstand stress from unpredictable directions.

What are the three types of cartilage and their main functions?

Hyaline cartilage (eases joint movement, holds airway open, precursor of bone), Fibrocartilage (resists compression and absorbs shock), and Elastic cartilage (provides flexible, elastic support).

What structural components compose bone tissue?

A calcified matrix arranged in concentric layers called lamellae around central canals, with osteocytes located in lacunae connected by canaliculi.

What are the components of blood and what is its primary function?

Blood consists of plasma (ground substance) and formed elements (red blood cells, white blood cells, and platelets); it transports gases, nutrients, wastes, chemical signals, and cells.

What two cell types make up nervous tissue, and what are their respective roles?

Neurons transmit signals, while Neuroglia (glial cells) protect and assist neurons.

What are the distinct physical features and locations of skeletal, cardiac, and smooth muscle tissues?

Skeletal muscle features long, thin, multinucleated, striated cells. Cardiac muscle consists of short, branched, striated cells with single nuclei and intercalated discs, found only in the heart. Smooth muscle features non-striated, fusiform cells found in visceral organ walls and blood vessels.

How is directionality in DNA strands established and oriented?

Directionality arises from nucleotide shape, featuring a $5'$ phosphate end and a $3'$ hydroxyl end, with the two strands running in opposite (antiparallel) orientations.

What are the centromere and kinetochore of a chromosome?

The centromere is a specialized DNA region where two sister chromatids are held together. The kinetochore is a protein complex at the centromere that serves as the attachment site for microtubules.

What is the biological definition of a gene?

A segment of DNA that carries information needed to produce an RNA molecule, which is usually involved in protein synthesis.

What structures compose a eukaryotic gene's open reading frame (ORF) and regulatory regions?

The open reading frame (ORF) contains exons (protein-coding sequences) and introns (non-coding sequences removed during processing). Regulatory sequences include the promoter, which indicates where RNA polymerase begins transcription.

What step-by-step process occurs during transcription?

RNA polymerase binds to the promoter -> DNA strands separate locally (~$20$ base pairs) -> RNA polymerase reads the template strand -> Complementary mRNA is built -> mRNA detaches and the DNA double helix re-forms.

What is alternative splicing and why is it important?

Alternative splicing is the post-transcriptional process where introns are removed and different combinations of exons are joined, allowing one gene to code for more than one protein.

What occurs during translation initiation?

The start codon (AUG) codes for methionine and signals the ribosome to begin; the small and large ribosomal subunits assemble around mRNA with initiator tRNA in the P site.

What are the three tRNA docking sites in a ribosome and their roles during elongation?

The A (Acceptor) site receives incoming tRNA; the P (Peptidyl) site holds tRNA attached to the growing polypeptide chain where peptide bonds form; the E (Exit) site releases deacylated tRNA.

What steps take place during the elongation stage of translation?

tRNA brings an amino acid to the A site -> Polypeptide chain is transferred from tRNA in the P site to tRNA in the A site via a peptide bond -> Ribosome translocates along mRNA -> Empty tRNA leaves from the E site -> Next tRNA enters the A site.

How is translation terminated?

A release factor binds to the A site when a stop codon (UAG, UAA, or UGA) is encountered, causing the completed polypeptide chain to be released and the ribosome subunits to dissociate.

Why is DNA replication described as semiconservative?

Each newly replicated DNA molecule contains one original parent strand and one newly synthesized strand.

What are the roles of DNA helicase, primase, DNA polymerase, and DNA ligase in DNA replication?

DNA helicase unzips the DNA molecule; Primase lays down a short RNA primer; DNA polymerase adds complementary bases in the $5' \rightarrow 3'$ direction and proofreads; DNA ligase seals gaps in the new DNA strand.

How does synthesis differ between the leading strand and lagging strand during DNA replication?

The leading strand is replicated continuously in the $5' \rightarrow 3'$ direction, whereas the lagging strand is replicated discontinuously in small sections (Okazaki fragments).

What activities take place during the $G_1$, S, and $G_2$ phases of interphase?

In $G_1$ phase, the cell grows and performs normal cellular functions. In S phase, DNA replication and centriole duplication occur. In $G_2$ phase, the cell prepares for mitosis and double-checks duplicated chromosomes for errors.

What do the $G_1$, $G_2$, and M checkpoints monitor in the cell cycle?

The $G_1$ Checkpoint determines if the cell enters S phase or rest in $G_0$; the $G_2$ Checkpoint determines if the cell can proceed to mitosis; the M Checkpoint (metaphase to anaphase) determines if sister chromatids can separate.

What type of cartilage tissue is depicted in the diagram and micrograph below?

Hyaline cartilage, characterized by a clear, glassy matrix and chondrocytes inside lacunae.

What type of muscle tissue is depicted in the diagram and micrograph below?

Cardiac muscle tissue, characterized by short, branched, striated cells with single nuclei and intercalated discs.