Cell Junctions and Gene Transcription

Flashcards covering key concepts related to cell junctions, cytoskeleton, and gene transcription processes.

Membrane bound proteins

1. Synthesized in the endoplasmic reticulum.
2. Targeted to various cellular membranes (e.g., plasma membrane, Golgi, lysosomes, peroxisomes) or secreted from the cell.
3. Play diverse roles as receptors, enzymes, transporters, and structural components.

Golgi apparatus

1. An organelle composed of flattened membranous sacs called cisternae.
2. Dedicated to sorting, modifying (such as glycosylation), and packaging proteins and lipids synthesized in the ER.
3. Functions for secretion or delivery to other organelles.
4. Has distinct cis, medial, and trans faces that process cargo sequentially.

Tight junctions

1. Multiprotein complexes (composed of claudins and occludins) found in epithelial and endothelial cells.
2. Create a selective barrier to molecular movement between cells by sealing the intercellular space.
3. Help maintain cell polarity.

Gap junctions

1. Channels composed of connexon proteins (each made of six connexins).
2. Allow for direct electrical and chemical cell-to-cell communication.
3. Permit the passage of ions, small solutes, and signaling molecules between adjacent cells.
4. Prominent in cardiac muscle, nerve cells, and certain epithelial cells.

Cytoskeleton

1. A dynamic network composed of three main types of protein filaments: microtubules, microfilaments, and intermediate filaments.
2. Provides structural support to the cell and maintains its shape.
3. Enables cell movement.
4. Facilitates intracellular transport and organizes organelles within the cytoplasm.

Microtubules

1. Hollow cylindrical structures made from polymerized alpha and beta tubulin protein dimers.
2. Are dynamic, constantly assembling and disassembling.
3. Function in maintaining cell shape.
4. Enable cell movement (as in cilia and flagella).
5. Form the mitotic spindle during cell division.
6. Serve as tracks for motor protein-mediated vesicle transport.

Motor molecules

1. Protein complexes (e.g., kinesins, dyneins, myosins).
2. Function in cellular motility by interacting with cytoskeleton components (microtubules or microfilaments).
3. Convert chemical energy from ATP hydrolysis into mechanical work.
4. Facilitate intracellular transport, muscle contraction, and cell shape changes.

Microfilaments

1. Dynamic, solid strands of actin protein.
2. Play a crucial role in cell structure and movement.
3. Involved in muscle contraction (forming the contractile apparatus with myosin), cell crawling, and cytokinesis (formation of the contractile ring).
4. Help maintain the shape of structures like microvilli.

Intermediate filaments

1. Tough, rope-like, insoluble protein fibers (e.g., keratins, vimentin, lamins).
2. Are less dynamic than microtubules and microfilaments.
3. Provide structural stability and tensile strength to cells.
4. Resist mechanical stress and anchor organelles.

Extracellular matrix

1. A complex network of macromolecules (such as collagen, elastin, proteoglycans, fibronectin, and laminin).
2. Secreted by cells, surrounds tissue layers and holds them together.
3. Provides structural support.
4. Regulates cell adhesion, migration, and differentiation.
5. Plays a role in intercellular communication.

Genome

1. The complete set of genetic material (DNA in most organisms, RNA in some viruses) present in an organism.
2. Includes all its genes, as well as non-coding sequences.
3. Non-coding sequences are essential for regulation, structure, and other cellular functions.

Genes

1. Specific sequences of DNA nucleotides.
2. Code for functional products, primarily specific proteins, but also various types of RNA (e.g., rRNA, tRNA, microRNAs).
3. Typically include both coding (exons) and non-coding (introns, regulatory) regions.

Exons

1. Regions within a gene that contain the coding sequences for proteins, ribosomal RNA (rRNA), or transfer RNA (tRNA).
2. These segments are retained and ligated together during mRNA processing.
3. Form the mature mRNA molecule that is subsequently translated into protein.

Introns

1. Non-coding segments of a gene.
2. Transcribed into pre-mRNA but are subsequently spliced out during mRNA processing, prior to translation.
3. Can play roles in gene regulation, alternative splicing, and evolutionary flexibility.

Chromosomes

1. Highly organized structures of DNA.
2. Tightly wrapped around specialized proteins called histones.
3. Found within the nucleus of eukaryotic cells (or in the cytoplasm of prokaryotes).
4. Contain the genetic information and become visible as distinct structures during cell division.

Nuclear envelope

1. A double lipid bilayer membrane that surrounds the nucleus in eukaryotic cells.
2. Separates the genetic material from the cytoplasm.
3. Its outer membrane is continuous with the endoplasmic reticulum.
4. Perforated by numerous nuclear pores that regulate the transport of molecules between the nucleus and cytoplasm.

Nucleolus

1. A prominent, non-membrane-bound structure within the nucleus of eukaryotic cells.
2. Its primary function is the synthesis