Module 1 Flashcards
CELL MEMBRANE
The nonpolar fatty acid tails of both leaflets make up the hydrophobic core of the membrane, providing the critical barrier that separates ICF from ECF.
NUCLEUS
The nucleus holds most of a cell’s DNA, with the remainder found in the mitochondria.
The nucleus also contains a nucleolus that functions in synthesis of ribosomes. Unless a cell is preparing to divide by mitosis, the nucleus contains DNA organized in chromosomes that are wound around histone proteins.
Red blood cells do not contain nuclei, and skeletal muscle cells have multiple nuclei.
RIBOSOMES
Ribosomes are manufactured in the nucleus from RNA and proteins and then migrate to the cytoplasm.
ROUGH ENDOPLASMIC RETICULUM
Within the rough endoplasmic reticulum, proteins fold to assume their secondary, tertiary, and (if applicable) quaternary structures. The rough endoplasmic reticulum is the site of chaperone proteins that detect the progress of protein folding and that mark misfolded proteins for destruction through the unfolded protein response.
SMOOTH ENDOPLASMIC RETICULUM
SER is the location of some steps in steroid hormone synthesis in certain endocrine gland cells. It is also the site of synthesis of new membranes that can refresh the cell membrane or organelle membranes. SER is a major site of cellular calcium homeostasis, sequestering calcium to keep cytoplasmic free calcium levels low most of the time, and releasing calcium in response to membrane receptor signaling,
In muscle cells, the specialized SER, called the sarcoplasmic reticulum, functions to release calcium ions that initiate muscle cell contraction, subsequently taking up calcium ions and causing muscle cell relaxation.
GOLGI APPARATUS
The Golgi apparatus is a stack of membranes organized in flattened sacks. It functions to sort, modify, and package proteins and lipids that are delivered in vesicles from the nearby endoplasmic reticulum.
After proceeding through the Golgi stacks, these substances may leave the cell by exocytosis or be delivered to different intracellular locations. The Golgi apparatus also forms other organelles that are vesicle-type organelles, including lysosomes and other secretory vesicles, as well as being a source of plasma membrane.
LYSOSOMES
Lysosomes contain degradative enzymes that break down aging cell organelles and molecules. The degradative enzymes are in the class called acid hydrolases, which depend on low pH for their function.
MECHANISMS OF MEMBRANE TRANSPORT
Diffusion occurs down a concentration gradient; that is, from an area of high concentration to an area of low concentration. Steroid and thyroid hormones are relatively nonpolar and hydrophilic, and are able to move across the cell membrane by simple diffusion
Facilitated diffusion is used to move polar or charged solutes down a concentration gradient. This is the most common way for glucose and amino acids to enter cells.
Active transport is a mechanism for moving a solute against its concentration gradient, which requires the input of energy. This process uses the sodium–potassium pump (Na+/K+ pump), also referred to as the sodium–potassium ATPase (adenosine triphosphatase)
Hypertrophy
Common adaptations include cell enlargement (hypertrophy) by addition of new cell components. As previously described, this is commonly seen in the cells of muscles after strength training.
Hyperplasia
For organs containing self-renewing cells, excessive hormone stimulation or workload increases organ mass and volume by hyperplasia—production of greater numbers of cells. This is seen in the uterus during pregnancy or in the thyroid gland during Graves disease, in which there is excessive stimulation of the thyroid-stimulating hormone receptor.
Atrophy
Denervation of muscles, disuse, or withdrawal of hormone stimulation results in cell atrophy—loss of cell volume or number. These losses are observable on visual inspection of muscle or imaging of organs as an overall decrease in size.
Metaplasia
Chronic mechanical or chemical stressors can cause cells to change their tissue-specific characteristics and develop metaplasia or an epithelial–mesenchymal transition—unstable cell forms with abnormal function and the potential to be transformed to cancer.
Dysplasia
Dysplasia is another form of cell transition in which proper quality control measures of cell division are lost, producing cells that are abnormal in appearance and are also precancerous.
Apoptotic Cell Death
Apoptosis is a very common mechanism of cell death that contributes to normal cell turnover, and there are many examples of the utility of apoptotic cell death.
Apoptosis is also known as programmed cell death because the steps follow an orderly sequence (a death program) and tissue disruption, organ dysfunction, and inflammation are minimized.
Steps in Apoptosis
Nuclear condensation and clumping of DNA
Enzymatic digestion of DNA into segments of uniform length
Nuclear membrane fragmentation
Cell membrane shrinkage—removal of small pieces of membrane and cytoplasm by blebbing
Blebbing—proceeds until the entire cell has been replaced by small fragments termed apoptotic bodies
Cellular debris and apoptotic bodies are phagocytosed by tissue macrophages
