תא Flashcards
eukaryote
חד תאים אצות פיטריות צומח בעלי חיים
prokaryote
חיידקים - תאים פשוטים יותר מבנה: 1 .דופן תא 2 .קרום תא DNA .3 4 .ציטופלסמה
minerals
מולקולות המתפרקות במים ליון חיובי ושלילי
acids
מולקולה המשחררת במים יוני מימן
base
מולקולה הקושרת אליה במים יוני מימן חופשיים
pH
רמת יוני המימן החופשיים שיש בתמיסה
proteins
פולימר. אבן הבניין: חומצה אמינית:
בטבע קיימות 20 חומצות אמיניות שונות
כשאבני הבניין מתחברות זו לזו נוצרת שרשרת
("פפטיד"
כשמספר "פפטידים" מתחברים - נוצר חלבון
תלת ממדי
רצפים שונים של חומצות אמיניות אחראיים למגוון
אינסופי של חלבוניםprotein structure
מבנה ראשוני
מבנה שניוני
מבנה שלישוני
מבנה רביעוני
Primary structure of protein
רצף חומצות אמיניות
Secondary structure of protein
התקפלות ספונטנית
“סלילי אלפא” או “משטח בטא”
Tertiary structure
קיפול של השרשרת
הפפטידית למבנה תלת מימדי
Quaternary structure
חיבור של מספר
שרשראות פפפטידיות (תת יחידות)
protein functions
מבנה וצורה נשאים הגנה חיסונית בקרה אנזימים
lipids
מולקולות שאינן נמסות (מתפרקות) במים (הידרופוביות)
ליפידים
לדוגמה: גליצרידים (“שומנים”), פוספוליפידים, כולסטרול, גליצרול
lipid functions
מתווכי דלקת וקרישת דם מאגר אנרגיה לטווח ארוך "שומן") (גליצרידים סטרואידים (כולסטרול) תמיכה מבנית קרומי התא מעטפת מיילין
sugar types
חד סוכרים (monosaccharides : (מולקולות אורגניות טבעתיות
דו סוכרים (disaccharides
רב סוכרים
:(polysaccharides)
glycogen
רב-סוכר המיוצר בכבד
ובשרירים (מאגר גלוקוז
קצר טווח)
sugar functions
1. נוקלאוטיד (RNA ,DNA) 2. גלוקוז - מקור מידי לאנרגיה 3. גליקופרוטאינים: חלבון עם קבוצות סוכר פרוטאוגליקאנים: רב-סוכר עם קבוצות חלבון 4. קצר טווח לאנרגיה גליקוגן – מאגר
signal transduction
מעבר של אות מחוץ התא אל תוך התא.
Cytoskeleton types
- microfilaments
- intermediate filaments
- microtubules
Cytoskeleton functions
צורה לתא
- עגינה לאברונים
- תנועת של בועיות בתא
- תנועת הכרומוזומים
- תנועת התא כולו
microfilaments
Microfilaments (mIˉ-kroˉ-FIL-a-ments) are
the thinnest elements of the cytoskeleton. They are composed of the proteins actin and myosin and are most prevalent at the edge of a cell (Figure 3.15a). Microfilaments have two general functions: They help generate movement and provide mechanical support. With respect to movement, microfilaments are involved in muscle contraction, cell division, and cell locomotion, such as occurs during the migration of embryonic cells during development, the invasion of tissues by white blood cells to fight infection, or the migration of skin cells during wound healing.
They anchor the cytoskeleton to integral proteins in the plasma membrane. Microfilaments also provide mechanical support for cell extensions called microvilli
intermediate filaments
As their name suggests, intermediate filaments are thicker than microfilaments but thinner than
microtubules . Several different proteins can compose intermediate filaments, which are exceptionally strong. They are found in parts of cells subject to mechanical stress; they help stabilize the position of organelles such as the nucleus and help attach cells to one another.
microtubules
Microtubules (mIˉ-kroˉ-TOO-buˉls), the largest of the cytoskeletal components, are long, unbranched hollow
tubes composed mainly of the protein tubulin. The assembly of microtubules begins in an organelle called the centrosome (discussed shortly). The microtubules grow outward from the centrosome toward the periphery of the cell . Microtubules help determine cell shape. They also function in the movement of organelles such as secretory vesicles, of chromosomes during cell division, and of specialized cell projections, such as cilia and flagella.
centriole
are cylindrical structures, each composed of nine clusters of three microtubules (triplets) arranged in a circular pattern
cilia
(SIL-e¯-a eyelashes; singular is cilium) are numerous, short, hairlike projections that extend from the surface of the cell. Each cilium contains a core of 20 microtubules surrounded by plasma membrane (Figure 3.17a). The microtubules are arranged such that one pair in the center is surrounded by nine clusters of two fused microtubules (doublets). Each cilium is anchored to a basal body just below the surface of the plasma membrane. A basal body is similar in structure to a centriole and functions in initiating the assembly of cilia and flagella.
flagellum
are similar in structure to cilia but are typically much longer. Flagella usually move an entire cell. A flagellum generates forward motion along its axis by rapidly wiggling in a wavelike pattern
Endoplasmic reticulum
The ER extends from the nuclear envelope (membrane around the nucleus), to which it is connected and projects throughout the cytoplasm. The ER is so extensive that it constitutes more than half of the membranous surfaces within the cytoplasm of most cells. Cells contain two distinct forms of ER, which differ in structure and function.
Ribosomes
consists of two subunits, one about half the size
of the other . The large and small subunits are made separately in the nucleolus. Once produced, the large and small subunits exit the nucleus separately, then come together in the cytoplasm.
Some ribosomes are attached to the outer surface of the nuclear membrane and to an extensively folded membrane called the endoplasmic reticulum. These ribosomes synthesize proteins destined for specific organelles, for insertion in the plasma membrane,
or for export from the cell. Other ribosomes are “free” or unattached to other cytoplasmic structures. Free ribosomes synthesize proteins used in the cytosol. Ribosomes are also located within mitochondria, where they synthesize mitochondrial proteins.
Golgi Complex
The first step in the transport pathway is through an organelle called the Golgi complex (GOL-je¯). It consists of 3 to 20 cisternae (sisTER-ne¯ cavities; singular is cisterna), small, flattened membranous sacs with bulging edges that resemble a stack of pita
bread (Figure 3.20). The cisternae are often curved, giving the Golgi complex a cuplike shape. Most cells have several Golgi complexes, and Golgi complexes are more extensive in cells that secrete proteins, a clue to the organelle’s role in the cell.
Different enzymes in the entry, medial, and exit cisternae of the Golgi complex permit each of these areas to modify, sort, and package proteins into vesicles for transport to different destinations.
The entry face receives and modifies proteins produced by the rough ER. The medial cisternae add carbohydrates to proteins to form glycoproteins and lipids to proteins to form lipoproteins. The exit face modifies the molecules further and then sorts and
packages them for transport to their destinations.
secretion vesicles Goldgi
These vesicles deliver the proteins to the plasma membrane, where they are discharged by exocytosis into the extracellular fluid. For example, certain pancreatic cells release the hormone insulin in
this way
transport vesicles
vesicle that moves protein from rER to Golgi
lysosome
Lysosomes (LIˉ-so¯-so¯ms; lyso- dissolving; -somes bodies) are membrane-enclosed vesicles that form from the Golgi complex (Figure 3.22). They can contain as many as 60 kinds of powerful digestive and hydrolytic enzymes that can break down a wide variety of molecules once lysosomes fuse with vesicles formed during endocytosis. Because lysosomal enzymes work best at an acidic pH, the lysosomal membrane includes active transport pumps that import hydrogen ions (H). Thus, the lysosomal interior has a pH of 5
מחלת גושה (disease s’Gaucher
מחלה תורשתית רצסיבית אוטוזומלית (שלוש צורות).
• נובעת מחסרונו של אחד מאנזימי הליזוזום (גלוקו-צרברו-זידאז) שנועד לסלק
• נזק בעיקר לתאי הכבד, הכליות מרכיבים שומנים מקרום התא.
הריאות, ומח העצם ( בצורות
מסוימות גם במוח).
Tay-Sachs disease
inherited condition characterized by the absence
of a single lysosomal enzyme called Hex A. This enzyme normally breaks down a membrane glycolipid called ganglioside GM2 that is especially prevalent in nerve cells. As the excess ganglioside GM2 accumulates, the nerve cells function less efficiently. Children with Tay-Sachs disease typically experience seizures and muscle rigidity.
They gradually become blind, demented, and uncoordinated and usually die before the age of 5. Tests can now reveal whether an adult is a carrier of the defective gene.
peroxisome
similar in structure to lysosomes, but
smaller, are the peroxisomes (pe-ROKS-i-so¯ms; peroxi- peroxide; -somes bodies; see Figure 3.1). Peroxisomes, also called microbodies, contain several oxidases, enzymes that can oxidize (remove hydrogen atoms from) various organic substances. For instance, amino acids and fatty acids are oxidized in peroxisomes
as part of normal metabolism. In addition, enzymes in peroxisomes oxidize toxic substances, such as alcohol.
Thus, peroxisomes are very abundant in the liver, where detoxification of alcohol and other damaging substances occurs.
A by-product of the oxidation reactions is hydrogen peroxide (H2O2), a potentially toxic compound, and associated free radicals such as superoxide.
However, peroxisomes also contain the enzyme catalase, which decomposes H2O2. Because production and degradation of H2O2
occur within the same organelle, peroxisomes protect other parts of the cell from the toxic effects of H2O2. Peroxisomes also contain enzymes that destroy superoxide. Without peroxisomes, byproducts of metabolism could accumulate inside a cell and result
in cellular death. Peroxisomes can self-replicate. New peroxisomes may form from preexisting ones by enlarging and dividing.
They may also form by a process in which components accumulate at a given site in the cell and then assemble into a peroxisome.
Proteasomes
Continuous destruction of unneeded, damaged, or faulty proteins is the function of tiny barrel-shaped structures consisting of four stacked rings of proteins around a central core called proteasomes (PRO¯-te¯-a-so¯ms protein bodies). For example, proteins that are part of metabolic pathways need to be degraded after they have accomplished their function. Such protein
destruction plays a part in negative feedback by halting a pathway once the appropriate response has been achieved. A typical body cell contains many thousands of proteasomes, in both the cytosol and the
nucleus. Discovered only recently because they are far too small to discern under the light microscope and do not show up well in electron micrographs, proteasomes were so named because they contain
myriad proteases, enzymes that cut proteins into small peptides.
Once the enzymes of a proteasome have chopped up a protein into
smaller chunks, other enzymes then break down the peptides into amino acids, which can be recycled into new proteins.
Mitochondria
Because they generate most of the ATP through aerobic (oxygenrequiring) respiration, mitochondria
are referred to as the “powerhouses” of the cell. A cell may have as few as a hundred or as many as several thousand mitochondria, depending on its activity. Active cells that use ATP at a high rate—such as those
found in the muscles, liver, and kidneys—have a large number of mitochondria. For example, regular exercise can lead to an increase in the number of mitochondria in muscle cells, which allows muscle cells to function more efficiently. Mitochondria are usually located
within the cell where oxygen enters the cell or where the ATP is used, for example, among the contractile proteins in muscle cells.
A mitochondrion consists of an outer mitochondrial membrane and an inner mitochondrial membrane with a small fluid-filled space between them (Figure 3.23). Both membranes are similar in structure to the plasma membrane. The inner mitochondrial membrane contains a series of folds called mitochondrial cristae (KRISte¯ ridges). The central fluid-filled cavity of a mitochondrion, enclosed by the inner mitochondrial membrane, is the mitochondrial matrix. The elaborate folds of the cristae provide an enormous surface area for the chemical reactions that are part of the aerobic phase of cellular respiration, the reactions that produce most of a cell’s ATP . The enzymes that catalyze these reactions are located on the cristae and in the matrix of the mitochondria. Mitochondria even have their own
DNA, in the form of multiple copies of a circular DNA molecule that contains 37 genes. These mitochondrial genes control the synthesis of 2 ribosomal RNAs, 22 transfer RNAs, and 13 proteins that build mitochondrial components.
apoptosis
Mitochondria also play an important and early role in apoptosis (ap-o¯p-TO¯-sis or ap-o¯-TO¯-sis a falling off), the orderly, geneti cally programmed death of a cell. In response to stimuli such as large numbers of destructive free radicals, DNA damage, growth factor
deprivation, or lack of oxygen and nutrients, certain chemicals are released from mitochondria following the formation of a pore in the outer mitochondrial membrane. One of the chemicals released into
the cytosol of the cell is cytochrome c, which while inside the mitochondria is involved in aerobic cellular respiration. In the cytosol,
however, cytochrome c and other substances initiate a cascade of activation of protein-digesting enzymes that bring about apoptosis.
nucleus
The nucleus is a spherical or oval-shaped structure that usually is the most prominent feature of a cell . Most cells have a single nucleus, although some, such as mature red blood cells, have none. In contrast, skeletal muscle cells and a few other types of cells have multiple nuclei.
nucleoplasm
חומר בגרעין
Chromatin
Human somatic (body) cells have 46 chromosomes, 23 inherited from each parent. Each chromosome is a long molecule of DNA that is coiled together with several proteins (Figure 3.25). This complex of DNA, proteins, and some RNA is called chromatin (KRO¯-matin).
PASSIVE PROCESSES types
1 Simple diffusion
2 .Facilitated diffusion
3 .Osmosis
ACTIVE PROCESSES
1 . Primary active transport/ Secondary active transport
2 .Endocytosis/ Exocytosis
3 .Phagocytosis/ Pinocytosis
diffusion
Movement of molecules or ions down a concentration gradient due to their kinetic energy until they reach equilibrium.
simple diffusion
Simple diffusion is a passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins .
Nonpolar, hydrophobic molecules move across the lipid bilayer through the process of simple diffusion. Such molecules include oxygen, carbon dioxide, and nitrogen gases; fatty acids; steroids;
and fat-soluble vitamins (A, D, E, and K). Small, uncharged polar molecules such as water, urea, and small alcohols also pass through the lipid bilayer by simple diffusion.
.
facilitated diffusion
Solutes that are too polar or highly charged to move through the lipid bilayer by simple diffusion can cross the plasma membrane by a passive process called facilitated diffusion. In this process, an integral membrane protein assists a specific substance across
the membrane. The integral membrane protein can be either a membrane channel or a carrier.
Diffusion of ions through channels is generally slower than free diffusion through the lipid bilayer because channels occupy a smaller fraction of the membrane’s total surface area than lipids. Still, facilitated diffusion through channels is a very fast process: More than a million potassium ions can flow through a K channel in one second!
Substances that move across the plasma membrane by carriermediated facilitated diffusion include glucose, fructose, galactose, and some vitamins. Glucose, the body’s preferred energy source for making ATP, enters many body cells by carrier-mediated
facilitated diffusion as follows
osmosis
Osmosis (oz-MO¯-sis) is a type of diffusion in which there is net movement of a solvent through a selectively permeable membrane. Like the other types of diffusion, osmosis is a passive process. In living systems, the solvent is water, which moves by
osmosis across plasma membranes from an area of higher water concentration to an area of lower water concentration. Another way to understand this idea is to consider the solute concentration: In osmosis, water moves through a selectively permeable membrane from an area of lower solute concentration to an area
of higher solute concentration. During osmosis, water molecules pass through a plasma membrane in two ways: (1) by moving between neighboring phospholipid molecules in the lipid bilayer via simple diffusion, as previously described, and (2) by moving through aquaporins (ak-wa-POR-ins; aqua- water), integral membrane proteins that function as water channels.
Active Transport
Active process in which a cell expends energy to move a substance across the membrane against its concentration gradient by transmembrane proteins that function as carriers. Polar or charged solutes.
Ion channel (integral)
Forms a pore through which a specific ion can flow to get across membrane. Most plasma membranes include specific channels for several common ions.
Carrier (integral)
Transports a specific substance across membrane by undergoing a change in shape. For example, amino acids, needed to synthesize new proteins, enter body cells via carriers. Carrier proteins are also known
as transporters.
Receptor (integral)
Recognizes specific ligand and alters cell’s function in some way. For example, antidiuretic hormone binds to receptors in the kidneys and changes the water permeability of certain plasma membranes.
Enzyme (integral and peripheral)
Catalyzes reaction inside or outside cell (depending on
which direction the active site faces). For example,
lactase protruding from epithelial cells lining your
small intestine splits the disaccharide lactose in the
milk you drink.
Cell identity marker (glycoprotein)
Distinguishes your cells from anyone else’s (unless
you are an identical twin). An important class of such
markers are the major histocompatibility (MHC) proteins.
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called histones which, aided by chaperone proteins, bind to and condense the DNA molecule to maintain its integrity.
symporter
A symporter is an integral membrane protein that is involved in the transport of many differing types of molecules across the cell membrane. The symporter works in the plasma membrane and molecules are transported across the cell membrane at the same time, and is, therefore, a type of cotransporter.
both directions - into the cell
antiporter
An antiporter (also called exchanger or counter-transporter) is a cotransporter and integral membrane protein involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions, one into the cell and one out of the cell. one in one out
