Cell structure Flashcards
Light microscope resolution
200 nm at 100x
Electron microscope resolution
Transmission EMs resolve 0.2 nm
Microscopic anatomy is the study of: (4 things)
Cells
Tissues
Organs
Systems
Plasma membrane
The specialized delimiting capsule (lipid bilayer)
Cytoplasm
transparent substance around the nucleus that fills the
rest of the cell’s interior (cytosol + many membrane-enclosed organelles)
Cell cortex
A specialized layer of cytoplasm consisting of a meshwork of fibrous proteins that reinforces the membrane. Provides polarized shape and movement
What are the 3 primary components of the cell cortex?
Actin filaments
microtubules
intermediate filaments
Glycocalyx function
Protects and lubricates, important in cell-cell recognition and adhesion
Glycocalyx structure
sugar coating of oligosaccharides and polysaccharides found on the exterior of the cell membrane (appears fuzzy)
Ribosomes structure and size
10-20 nm cytoplasmic particles composed of rRNAs and ribosomal proteins (appear purple (basophilia) when stained)
2 locations of ribosomes
- Free in cytoplasm in clusters (polyribosomes)
- Associated with the membranes of the RER
Rough Endoplasmic Reticulum (RER)
Plays a central role in the synthesis and export of proteins and glycoproteins. Is covered in ribosomes
Smooth Endoplasmic Reticulum (SER) 3 functions
- Involved in the synthesis of lipids (steroids)
- Metabolism of lipid soluble substances
- Regulated concentration of calcium in all cells (including muscle cells)
Golgi Apparatus function
Post-translational modifications of proteins
Golgi apparatus structure
Flattened membrane bound sacs(cisternae) piled in stacks like plates
Lysosomes definition
membranous sacs
of hydrolytic enzymes (such as
nuclease, proteases, lipases,
etc.)
4 functions of lysosome
- Phagocytosis
- Autophagy (degredation of internal organelles when they become obselete)
- Excretion of hydrolytic enzymes
- Autolysis
Peroxisome (like hydrogen perioxide)
Help to manage free radicals, also regulate H2O2 metabolism
Melanosome
Absorbs UV light
Centrioles
Microtuble organizing center
Mitochondria
Energy source; produces ATP, heat, and most cellular reactions. Shape varies from rods to spheres
Proteasome function
degrades
intracellular proteins marked for
destruction by attachment of
multiple ubiquitin molecules
Protease abnormality
Leads to degenerative diseases and some cancers
Glycogen
a large branched polysaccharide (stored glucose) found in liver, muscle, etc. cell cytoplasm
Pigment granules
- melanin
- heme(breakdown product of hemoglobin degeneration)
Secretory granules
membrane bound vesicles that contain inactive enzymes, proteins, neurotransmitters, mucus, etc.
Cytoskeleton definition
System of protein filaments in the cytoplasm, continuously reorganizing
Cytoskeleton function
- cell movement
- intracellular movement and transport
- mitosis/meiosis
Microtubules
long, stiff, cylindrical intracellular structures (20 nm diameter) composed of the protein tubulin
Microtubule orientation
Are polar; Negative end is in the centrosome, positive end outward
Motor proteins
Bind organelles and move them along microtubules
Intermediate filaments
Intermediat in size (10 nm in diameter). Gives mechanical strength
Actin filaments
Small (7 nm in diameter) filamentous protein formed in a chain of globular actin molecules.
Actin filaments function
- Involved in cell movement (crawling)
- Muscle contraction
Nucleus
Most prominent organelle in a eukaryotic cell, contains DNA organized into chromosomes
Nuclear envelope
The envelope surrounding the nucleus (consists of 2 lipid bilayer membranes). perforated by nuclear pores and supported internally by nuclear lamina
Nuclear pores
Perforations in the nuclear envelope that transport selected molecules
Nucleolus
Region of the nucleus where different chromosomes carrying genes for ribosomal RNA cluster together
Chromatin
Complex of DNA histones and nonhistone proteins from which chromosomes are made
Chromatin characteristics
- Stains basophilically
- one DNA strand/chromosome
- organized around the nucleosome
Chromatin function
Histone proteins play a critical role in regulating gene expression because they can alter the accessibility of gene sequences in DNA
Chromatin types (2)
Heterochromatin and euchromatin
Heterochromatin
Highly condensed form of interphase chromatin, transcriptionally inactive, stains dark
Euchromatin
Least condensed, extended state of chromatin, transcriptionally active, stains lightly,
The cell cycle
Sequence of events by which a cell duplicates it contents and divides in two
Four cell cycle phases
- M phase
- G1 phase
- S phase
- G2 phase
M phase(mitosis)
Chromosomes are condensed and the nucleus and cytoplasm divide. (consists of 6 steps)
Cytokinesis
- Division of the cytoplasm (last step of M phase)
- Contractile ring creates cleavage furrow
- When finished 2 new complete cells are ready
G1 phase (g=gap or “growth”)
The interval between the end of mitosis and the beginning of S phase, most quiescent cells rest here
S phase (s=synthesis)
The cell replicates its nuclear DNA (prerequisite for division)
G2 Phase (g=gap or “growth”)
The interval between the end of S phase and the beginning of mitosis
Interphase
G1, S, and G2 phases are part of interphase.
-During interphase the cell increases in size. The DNA of the chromosomes is replicated and centrosome is duplicated.
6 steps of M phase
- Prophase
- prometaphase
- metaphase
- anaphase
- telophase
- cytokinesis
Prophase
Chromosomes start to condense, mitotic spindle forms, nucleolus disappears
Prometaphase
Mitotic spindle captures and organizes chromosomes, chromosomes finish condensing.
-nuclear envelope breaks down releasing chromosomes
Metaphase
- Spindle lines chromosomes at middle of cell.
- Kinetochores are attached to microtubules at opposite spindle poles
Anaphase
- Sister chromatids seperate and are pulled to opposite ends
- Microtubules elongate and push apart (kinetochores also pull chromosomes towards poles)
Telophase
- Chromosomes start to decondense(return to “stringy” form)
- Spindle disappears
- Nuclear membrand re-forms and nucleolus reappears
3 cell cycle checkpoints
- G2/M checkpoint
- Spindle checkpoint
- Restriction Checkpoint
G2/M Checkpoint
Unreplicated DNA will prevent entry into M phase (mitosis)
Spindle Checkpoint
Improper assembly of the mitotic spindle leads to arrest in anaphase (chromosomes not aligned properly)
restriction Checkpoint (G1 checkpoint)
Prevents entry into S phase until all DNA damage is repaired
