Synthesis and induction of tyrosine aminotransferase in synchronized hepatoma cells in culture. Mayol, R. Synthesis of estrogen-specific proteins in the uterus of the immature rat. Biochemistry, McAuslan, B. The induction and repression of thymidine kinase in the poxvirus-infected HeLa cell. McCarl, R. The effects of actinomycin D on protein synthesis and beating in cultured rat heart cells. Moscona, A. Moscona, and R. Induction of glutamine synthetase in embryonic neural retina in vitro by inhibitors of macromolecular synthesis.
Moscona, and N. Enzyme induction in embryonic retina: The role of transcription and translation. Nebert, D. Fate of inducer during induction of aryl hydrocarbon hydroxylase activity in mammalian cell culture. Substrate-inducible microsomal aryl hydroxylase in mammalian cell culture. Noguchi, T. Stimulatory effect of actinomycin D on arginase activity in anuran tadpole liver during metamorphosis.
Tokyo, Sec. IV, In vitro hormonal induction of a specific protein avidin in chick oviduct. Perry, R. Messenger RNA-protein complexes and newly synthesized ribosomal subunits: analysis of free particles and components of polyribosomes.
Peterkofsky, B. Effect of inhibitors of nucleic acid synthesis on steroid-mediated induction of tyrosine aminotransferase in hepatoma cell cultures. Evidence for the steroid-induced accumulation of tyrosine aminotransferase messenger RNA in the absence of protein synthesis.
Prichard, P. Gilbert, D. Shafritz, and W. Factors for the initiation of haemoglobin synthesis by rabbit reticulocyte ribosomes. Ptashne, M. Reif-Lehrer, L. Hydrocortisone requirement for the induction of glutamine synthetase in chick-embryo retinas. Rivlin, R. Regulation of hepatic fat levels by thyroid hormone. Advances Enzym. Roberts, J. Termination factor for RNA synthesis. Rubin, M. On the nature of allosteric transitions: Implications of non-exclusive ligand binding.
Samuels, H. The relation of steroid structure to enzyme induction in hepatoma tissue culture cells. Scarano, E. Studies on the control of enzyme synthesis during the early embryonic development of sea urchins. Schimke, R. Sweeny, and C. The roles of synthesis and degradation in the control of rat liver tryptophan pyrrolase. Sherman, F. Stewart, J. Parker, G. Putterman, B. Agrawal, and E. The relationship of gene structure and protein structure of ISO-i-cytochrome c from yeast.
Singhal, R. Vijayvargiya, and G. Cyclic adenosine monophosphate: andromimetic action on seminal vesicular enzymes. Smith, A. Cytoplasmic methionine transfer RNAs from eukaryotes. Steiner, D. Cunningham, L. Spigelman, and B. Insulin biosynthesis: Evidence for a precursor. Stellwagen, R. Dritz, and G. Stubbs, D. Effects of actinomycin D and puromycin on induction of gulonolactone hydrolase by somatotrophic hormone. Summers, D. Evidence for large precursor proteins in poliovirus synthesis.
Sussman, A. Protein turnover in amino acid-starved strains of Escherichia coli K differing in their ribonucleic acid control. Thompson, E. Superinduction of tyrosine aminotransferase by actinomycin D in HTC cells. Granner, G. Tomkins, and J. Induction of tyrosine a-ketoglutarate transaminase by steroid hormones in a newly established tissue culture cell line. Tomkins, G. The operon concept in bacteria and higher organisms. Cancer Inst. Ames, and D. Hormones and gene action.
Gelehrter, D. Granner, B. Peterkofsky, and E. Regulation of gene expression in mammalian cells. Samuels, and E. Control of specific gene expression in higher organisms. Ames, T. Stellwagen, J. Baxter, P. Mamont, and B. Regulation of specific protein synthesis in eukaryotic cells.
Cold Spring Harbor Symp. All rights reserved. Mitochondria — often called the powerhouses of the cell — enable eukaryotes to make more efficient use of food sources than their prokaryotic counterparts.
That's because these organelles greatly expand the amount of membrane used for energy-generating electron transport chains. In addition, mitochondria use a process called oxidative metabolism to convert food into energy, and oxidative metabolism yields more energy per food molecule than non-oxygen-using, or anaerobic , methods. Energywise, cells with mitochondria can therefore afford to be bigger than cells without mitochondria. Within eukaryotic cells, mitochondria function somewhat like batteries, because they convert energy from one form to another: food nutrients to ATP.
Accordingly, cells with high metabolic needs can meet their higher energy demands by increasing the number of mitochondria they contain. For example, muscle cells in people who exercise regularly possess more mitochondria than muscle cells in sedentary people. Prokaryotes, on the other hand, don't have mitochondria for energy production, so they must rely on their immediate environment to obtain usable energy.
Prokaryotes generally use electron transport chains in their plasma membranes to provide much of their energy. The actual energy donors and acceptors for these electron transport chains are quite variable, reflecting the diverse range of habitats where prokaryotes live.
In aerobic prokaryotes, electrons are transferred to oxygen, much as in the mitochondria. The challenges associated with energy generation limit the size of prokaryotes. As these cells grow larger in volume, their energy needs increase proportionally. However, as they increase in size, their surface area — and thus their ability to both take in nutrients and transport electrons — does not increase to the same degree as their volume.
As a result, prokaryotic cells tend to be small so that they can effectively manage the balancing act between energy supply and demand Figure 6. Figure 6: The relationship between the radius, surface area, and volume of a cell Note that as the radius of a cell increases from 1x to 3x left , the surface area increases from 1x to 9x, and the volume increases from 1x to 27x. This page appears in the following eBook. Aa Aa Aa. Eukaryotic Cells. Figure 1: A mitochondrion.
Figure 2: A chloroplast. What Defines an Organelle? Why Is the Nucleus So Important? Why Are Mitochondria and Chloroplasts Special? Figure 4: The origin of mitochondria and chloroplasts. Mitochondria and chloroplasts likely evolved from engulfed bacteria that once lived as independent organisms. Figure 5: Typical prokaryotic left and eukaryotic right cells. In prokaryotes, the DNA chromosome is in contact with the cellular cytoplasm and is not in a housed membrane-bound nucleus.
Figure 6: The relationship between the radius, surface area, and volume of a cell. Note that as the radius of a cell increases from 1x to 3x left , the surface area increases from 1x to 9x, and the volume increases from 1x to 27x. Organelles serve specific functions within eukaryotes, such as energy production, photosynthesis, and membrane construction. Most are membrane-bound structures that are the sites of specific types of biochemical reactions.
The nucleus is particularly important among eukaryotic organelles because it is the location of a cell's DNA. Two other critical organelles are mitochondria and chloroplasts, which play important roles in energy conversion and are thought to have their evolutionary origins as simple single-celled organisms. Cell Biology for Seminars, Unit 1.
Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Creature Cast. Simply Science. Green Screen. The motor domains generate movement along microtubules. Most kinesins walk toward the plus end of microtubules, whereas dynein walks toward the minus end. This gives cells two tools to control the distribution of organelles along microtubules.
Kinesins and dyneins also contain a cargo-binding domain that links them to different organelles. Kinesins are a large family of proteins and the cargo binding domain is the most divergent, allowing different members of the kinesin family to bind different organelles. Dynein is a large complex of several proteins and how it binds cargo is less clear. Actin filaments also support the transport of cellular material but over much shorter distances than microtubules.
Actin filaments are a polymer of actin which is a small globular protein. The actin filament is a helical array of actin and similar to microtubules has a plus and minus end with filaments growing more readily from their plus ends. Actin filaments lack the extensive lateral contacts of microtubules and usually are much shorter than microtubules. Actin filaments tend to localize near the cell membrane where they provide structural support. Myosins are a class of motor proteins that can generate force along actin filaments.
Some myosins are involved in cell contraction i. Class V myosins are involved in the transport of organelles in several different types of cells. Similar to the structure of kinesin, class V myosins contain a motor domain that binds actin filaments and use the energy of ATP hydrolysis to walk along filaments.
The C-terminus of myosin V binds organelles. To transport and position organelles, cells often use both microtubules and actin filaments. Microtubules, kinesins and dyneins are used to move organelles over long distances several microns or more , whereas actin filaments transport organelles over short distances e.
Often an organelle will contain more than one type of motor protein e. To maintain the identity and function of the different organelles and plasma membrane, cells need to target specific proteins to organelles and other intracellular compartments.
Most of these proteins contain a short sequence, called a signal sequence, that determines their intracellular location. Signal sequences can be localized anywhere in a protein but are often found in the N-terminus. Signal sequences that target proteins to the same organelle often do not share the same primary sequence. It is usually the overall biochemical properties of the sequence that determine whether it targets a proteins to an organelle.
Signal sequences are used to import both soluble proteins and integral membrane proteins. Because the membranes that surrounds organelles restricts the passage of proteins, organelles have evolved different mechanisms for importing proteins from the cytoplasm. Most organelles contain a set of membrane proteins that form a pore. This pore allows the passage of proteins with the correct signal sequence. Some pores ER, mitochondria can only accommodate unfolded proteins, whereas other pores nucleus, peroxisome allow folded proteins to pass.
Proteins destined for secretion, the plasma membrane or any organelle of the secretory pathway are first inserted into the ER. Most proteins cross the ER co-translationally, being synthesized by ribosomes on the ER. Both soluble proteins proteins that reside in the lumen of organelles or are secreted and integral membrane proteins are targeted to the ER and translocated by the same mechanism. The signal sequence for ER proteins usually resides at the N-terminus.
The signal recognition particle SRP , a complex of 6 proteins and one RNA, binds the signal sequence immediately after it is translated. The SRP also interacts with the ribosome and stops translation. Ribosomes on the ER membrane bind to the protein translocator.
The translocator is a transmembrane protein that forms a aqueous pore. The pore is the channel through which the newly synthesized ER proteins will be translocated across the ER membrane.
Soluble proteins are completely translocated through the channel; the signal sequence remains in the channel and is cleaved from the rest of the protein by a protease in the lumen of the ER. Integral membrane proteins contain a stop transfer sequence downstream from the signal sequence.
The stop transfer sequence ceases translocation through channel and the portion of the protein after the stop transfer sequence resides outside the ER. Integral membrane proteins can be translocated such that either their N-terminus or C-terminus resides in the lumen of the ER.
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