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Cytoplasm: The part of a cell that contains the Cytosol and small structures excluding the Cell nucleus; Mitochondria; and large Vacuoles. (Glick, Glossary of Biochemistry and Molecular Biology, 1990)

Secondary Active Transport

JoVE 10707

One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this process is sodium (Na+), which is typically present in higher concentrations extracellularly than in the cytosol. Such a concentration difference is due, in part, to the action of an enzyme “pump” embedded in the cellular membrane that actively expels Na+ from a cell. Importantly, as this pump contributes to the high concentration of positively-charged Na+ outside a cell, it also helps to make this environment “more positive” than the intracellular region. As a result, both the chemical and electrical gradients of Na+ point towards the inside of a cell, and the electrochemical gradient is similarly directed inwards. Sodium-glucose cotransporters (SGLTs) exploit the energy stored in this electrochemical gradient. These proteins, primarily located in the membranes of intestinal or kidney cells, help in the absorption of glucose from the lumen of these organs into the bloodstream. In order to function, both an extracellular glucose molecule and two Na+ must bind to the SGLT. As Na+ migrates into a cell through the transporter, it travels with its electrochemical gradient, expelling energy that the protein uses to move glucose ins

 Core: Biology

Responses to Heat and Cold Stress

JoVE 11119

Every organism has an optimum temperature range within which healthy growth and physiological functioning can occur. At the ends of this range, there will be a minimum and maximum temperature that interrupt biological processes.

When the environmental dynamics fall out of the optimal limit for a given species, changes in metabolism and functioning occur – and this is defined as stress. Plants respond to stress by initiating changes in gene expression - leading to adjustments in plant metabolism and development aimed at attaining a state of homeostasis. Plants maintain membrane fluidity during temperature fluctuations Cell membranes in plants are generally one of the first structures that are affected by a change in ambient temperature. These membranes primarily constitute phospholipids, cholesterol, and proteins, with the lipid portion comprising long chains of unsaturated or saturated fatty acids. One of the primary strategies plants can adopt under temperature change is to alter the lipid component of their membranes. Typically, plants will decrease the degree of unsaturation of membrane lipids under high temperature, and increase it under low temperature, maintaining the fluidity of the membrane. Heat Shock Proteins The exposure of plant tissue or cells to sudden high-temperature stress res

 Core: Biology

Contact-dependent Signaling

JoVE 10715

Contact-dependent signaling uses specialized cytoplasmic channels between cells that allow the flow of small molecules between them. In animal cells, these channels are called gap junctions. In plants, they are known as plasmodesmata.

Gap junctions form when two hemichannels, or connexons, join; one connexon from one cell coupling to a connexon of an adjacent cell. Each cell’s connexon is formed from six proteins creating a circular channel. There are over 20 different types of these proteins, or connexins, so there is substantial variation in how they come together as connexons and as gap junctions. Connexins have four transmembrane subunits with both their N- and C-terminus endings located intracellularly. The C-terminus has multiple phosphorylation sites so it can be activated by numerous different kinases- further adding to gap junction variety. Depending on the activating kinase, and the C-terminal amino acid residues of connexins that are phosphorylated, gap junctions can be partially or fully opened. This selectively allows small molecules to flow from one cell into another. A gap junction may also exclude by electrochemical charge. The selectivity of gap junctions allows a single cell to coordinate a complex multicellular response. However, some toxic molecules, matching the size and electrochemical preference of the gap junction, can also p

 Core: Biology

Cell Structure - Prep Student

JoVE 10631

Visualizing Onion and Cheek Cells
Immediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and cut the onion in half with a knife. Pull apart the layers of the onion. The thin, nearly transparent film layers within the onion will be used by the students.
Place the onion film into a Petri…

 Lab Bio

Fundamentals of Breeding and Weaning

JoVE 10293

Source: Kay Stewart, RVT, RLATG, CMAR; Valerie A. Schroeder, RVT, RLATG. University of Notre Dame, IN

Millions of mice and rats are bred for use in biomedical research each year. Worldwide, there are several large commercial breeding facilities that supply mice to research laboratories, but many facilities choose to also breed mice and…

 Lab Animal Research

Biological Clocks and Seasonal Responses

JoVE 11116

The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod. One example of photoperiodism in plants is seasonal flowering. Scientists believe that plants are cued to flower by the correspondence of their circadian clocks to changes in the photoperiod. They detect these changes using light-sensitive photoreceptor systems. Phytochromes are a group of photoreceptors involved in flowering and other light-mediated processes. The phytochrome system enables plants to compare the duration of dark periods over several days. Short-day (long-night) plants flower after a minimum number of consecutive long nights. Long-day (short-night) plants, by contrast, initiate flowering following a minimum number of consecutive short nights. Phytochromes exist as two interconvertible forms: Pr and Pfr. Pr is converted into Pfr during the day, so Pfr is more abundant in daylight hours. Pfr is converted into Pr at night, so there is more Pr at nighttime. Therefore, plants can determine the length of the day-night cycle by me

 Core: Biology

The Apoplast and Symplast

JoVE 11106

Plant growth depends on its ability to take up water and dissolved minerals from the soil. The root system of every plant is equipped with the necessary tissues to facilitate the entry of water and solutes. The plant tissues involved in the transport of water and minerals have two major compartments - the apoplast and the symplast. The apoplast includes everything outside the plasma membrane of living cells and consists of cell walls, extracellular spaces, xylem, phloem, and tracheids. The symplast, in contrast, consists of the entire cytosol of all living plant cells and the plasmodesmata - which are the cytoplasmic channels interconnecting the cells. There are several potential pathways for molecules to move through the plant tissues: The apoplastic, symplastic, or transmembrane pathways. The apoplastic pathway involves the movement of water and dissolved minerals along cell walls and extracellular spaces. In the symplastic route, water and solutes move along the cytosol. Once in this pathway, materials need to cross the plasma membrane when moving from cell to neighboring cell, and they do this via the plasmodesmata. Alternatively, in the transmembrane route, the dissolved minerals and water move from cell to cell by crossing the cell wall to exit one cell and enter the next. These three pathways are not mutually exclusive, and some solutes may use more than on

 Core: Biology

Phloem and Sugar Transport

JoVE 11101

Like many living organisms, plants have tissues that specialize in specific plant functions. For example, shoots are well adapted to rapid growth, while roots are structured to acquire resources efficiently. However, sugar production is primarily restricted to the photosynthetic cells that reside in the leaves of angiosperm plants. Sugar and other resources are transported from photosynthetic tissues to other specialized tissues by a process called translocation. Within a plant, tissues that produce more sugar than they consume are sugar sources - leaves are the primary example of this. Roots, shoots, flowers, and fruits are usually considered to be sugar sinks, as they require more sugar than they can make. Translocation distributes sugar, hormones, amino acids, and some signaling molecules from sugar sources to sugar sinks through a tube-like structure of vascular plants called phloem. Flow can be bidirectional in the phloem, which is composed of cells joined end-to-end by plasmodesmata to form the sieve-tube elements. These cells have thickened cell walls, giving them mechanical support, and are accompanied by neighboring companion cells that facilitate phloem health and loading of solutions into the phloem from surrounding tissues. Phloem loading can occur via the apoplastic or symplastic routes and may be either passive or active. These pathways to phl

 Core: Biology

RNA Stability

JoVE 11009

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations between RNA and DNA underlie the differences in their stability and longevity. Because DNA is double-stranded, it is inherently more stable. The single-stranded structure of RNA is less stable but also more flexible and can form weak internal bonds. Additionally, most RNAs in the cell are relatively short, while DNA can be up to 250 million nucleotides long. RNA has a hydroxyl group on the second carbon of the ribose sugar, increasing the likelihood of breakage of the sugar-phosphate backbone. The cell can exploit the instability of RNA, regulating both its longevity and availability. More stable mRNAs will be available for translation for a longer period of time than less stable mRNAs transcripts. RNA binding proteins (RBPs) in cells play a key role in the regulation of RNA stability. RBPs can bind to a specific sequence (AUUUA) in the 3’ untranslated region (UTR) of mRNAs. Interestingly, the number of AUUUA repeats appears to recruit RBPs in a specific way: fewer repeats recruit stabilizing RBPs. Several, overlapping repeats result in the binding of destabilizing RBPs. All cells have enzymes called RNases that break down RNAs. Typically, the 5’cap and polyA tail protect eukaryotic mRNA from degradation

 Core: Biology

Outcomes of Glycolysis

JoVE 11006

Nearly all the energy used by cells comes from the bonds that make up complex, organic compounds. These organic compounds are broken down into simpler molecules, such as glucose. Subsequently, cells extract energy from glucose over many chemical reactions—a process called cellular respiration.

Cellular respiration can take place in the presence or absence of oxygen, referred to as aerobic and anaerobic respiration, respectively. In the presence of oxygen, cellular respiration starts with glycolysis and continues with pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation. Both aerobic and anaerobic cellular respiration start with glycolysis. Glycolysis yields a net gain of two pyruvate molecules, two NADH molecules, and two ATP molecules (four produced minus two used during energy-requiring glycolysis). In addition to these major products, glycolysis generates two water molecules and two hydrogen ions. In cells that carry out anaerobic respiration, glycolysis is the primary source of ATP. These cells use fermentation to convert NADH from glycolysis back into NAD+, which is required to continue glycolysis. Glycolysis is also the primary source of ATP for mature mammalian red blood cells, which lack mitochondria. Cancer cells and stem cells rely on aerobic glycolysis for ATP. Cells that use aerobic respirati

 Core: Biology
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