الجمعة، 7 نوفمبر 2008
الجمعة، 31 أكتوبر 2008
epithelial tissies
epithelial Simple Squamous Endothelial Tissue
a nucleus of a cell forming the alveolus wall b nucleus of a cell forming the capillary wall c red blood cells inside capillary that will carry exchanged gases between the lungs and blood d cell that forms the large circle of simple squamous forming the alveolus. found: line lungs; line blood vessels (endothelium) function: adapted for osmosis, diffusion and secretion
Simple Cuboidal Epithelial Tissue
The lumen receives the secretion produced by the cuboidal cells
The black circle is superimposed on the basement membrane which holds t
ogether a circle of cuboidal cells.
found: line kidney tubules; cover ovaries; glands
function: adapted for secretion of fluid like mucus or enzymes; absorption (microvilli increase surface area)
The black circle is superimposed on the basement membrane which holds t
ogether a circle of cuboidal cells.found: line kidney tubules; cover ovaries; glands
function: adapted for secretion of fluid like mucus or enzymes; absorption (microvilli increase surface area)
Simple Columnar Epithelial Tissue
The fuzzyness on top of the simple columnar cells is caused by tiny microvilli.
found: i
n GI tract and uterus;
function: absorption of foods (microvilli); move sperm (cilia); secretion of mucus (goblet cells). Back to Epithelial Menu
found: i
n GI tract and uterus;function: absorption of foods (microvilli); move sperm (cilia); secretion of mucus (goblet cells). Back to Epithelial Menu
Pseudostratified Epithelial Tissue
a nuclei of pseudostratified columnar cells
found: respiratory tract; paranasal sinuses
function: protection, produce mucus, trap and move dust and other toxins out of the lungs. Back to Epithelial Menu
found: respiratory tract; paranasal sinuses
function: protection, produce mucus, trap and move dust and other toxins out of the lungs. Back to Epithelial Menu
Stratified Squamous Epithelial Tissue
a bracket is around the many rows of cells that belong to the stratified squamous epithelial tissue b dead surface layers found: epidermal layer of skin; lines mouth, esophagus, vagina and anal canal function: wall of protection against waterloss, abrasion infection, etc. Back to Epithelial Menu
Tran
sitional Epithelial Tissue
collapsed layers of the transitional cells b surface of the collapsed ureter
found: walls that line the urinary tract and bladder
function: able to stretch when an organ expands Back to Epithelial Menu
sitional Epithelial Tissuecollapsed layers of the transitional cells b surface of the collapsed ureter
found: walls that line the urinary tract and bladder
function: able to stretch when an organ expands Back to Epithelial Menu
Vocabulary
Vocabulary
Levels of organization
Matter in living beings is organized in a series of levels of increasing complexity, ranging from the atomic level to the multicellular level with tissues and organs. Only plants and animals reach the highest one, whereas bacteria stay at the unicellular level.
Bioelements
The most abundant chemical elements in a livig being, which are not much the same ones that you can find in a rock. The top six are C, H, O, N, P, S, and they're called the primary bioelements.
Biomolecules
The most abundant types of molecules in living beings are always the same ones, no matter if it is a bacterium or a human. They may be organic (with a skeleton of carbon atoms: carbohydrates, lipids, proteins, nucleic acids) or inorganic (without it: water, mineral salts).
Cell
The basic unit of Life. If something is not made up of cells, then it is not a living being. Cells can reproduce and interact with their environment (exchanginng matter and energy, and being able to notice its features). All cells have a plasma membrane, some organelles and genetic material.
Genetic material
In all cells the genetic material is DNA associated to proteins and organized in chromosomes. Bacteria have one chromosome, while humans have 46 in each cell. Its function is to store, express and transmit to the offspring the instructions that tell how every cell and living being will be self-constructed and how will they work.
Prokaryotic / Eukaryotic
Cells without a real nucleus (no nuclear membrane) are the first type. Cells with a real nucleus (genetic material enclosed in a nuclear membrane) are the second type. Bacteria and Archaea are prokayotes; Algae, Protozoa, Fungi, Plants and Animals are eukaryotes.
Mitosis
Cells with more than one chromosome, once they've synthesized a full copy of the whole set of chromosomes, have to carefully organize their division in order to produce two daughter-cells with exactly the same genetic information. Mitosis is the complex process whereby most eukaryotic cells tackle such a task.
Tissues
In multicellular beings there may be different types of cells, each type being specialized in an specific function, and having the specific shape that allows them to fulfill that function the best. Each of those types is called a cellular tissue; examples are the vascular tissue (plants) or the blood tissue (animals). One tissue may have several subtypes of cells (e.g. white blood cells and red blood cells).
Organs / Organ Systems
There are some tasks in a multicellular being that must be achieved by cells of different kinds working together (such as pumping blood throughout the human body). In this case, cells of different tissues gather and make up an organ (epithelial, connective, muscle and adipose cells make up the heart). Several organs working together in a common general task make up an organ system (the heart and the blood vessels make up the circulatory system).
Autotrophs / Heterotrophs
Or Producers and Consumers. The former don't feed off other living beings: they transform inorganic substances to produce the organic substances they need; plants and algae are autotrophs. The latter need to feed on other beings and then transform the organic substances they have eaten into their own organic substances (i.e.: your proteins come partly from the proteins in that beef-steak you ate yesterday); animals, fungi and protozoa are heterotrophs.
Common Structures in Eukaryotic Cells
Description
Function
Where
Cell Wall
Outermost layer on a plant cell composed of cellulose and other complex carbohydrates.
Helps to support and protect the cell.
P
Cell Membrane
Outer layer composed of lipids and proteins.
Controls the permeability of the cell to water and dissolved substances.
A, P
Flagella (flagellum)
Long and scarce threadlike structures that extends from the surface of the cell.
Used for movement of the cell or to move fluids over the cell's surface for absorption.
A
Cilia (cilium)
Short and abundant threadlike structures that extends from the surface of the cell.
Used for movement of the cell or to move fluids over the cell's surface for absorption.
A
Cytoplasm
Semifluid mixture that occupies most of the cell's interior. Contains sugars, aminoacids, and proteins. Also, contains a protein fiber network.
Medium in which organelles and other internal structures exist in. Fiber network support the shape of the cell and anchor organelles to fixed positions.
A, P
Mitochondria (mitochondrion)
Elongated organelles enclosed in a double membrane, the inner one being creased
Sites of respiration: converts sugars and fats into energy through oxidation.
A, P
Chloroplasts
Elongated organelles enclosed in a double membrane and with vesicles containing chlorophyll.
Sites of photosynthesis.
P
Ribosomes
Tiny organelles composed of protein and RNA, not enclosed in a membrane. Often attached to endoplasmic reticulum.
Sites of protein synthesis.
A, P
Endoplasmic Reticulum
Extensive system of internal membranes. May be smooth or rough: the latter has ribosomes attached to its membrane.
Site of transport and synthesis of various cell substances.
A, P
Golgi Complex
Flattened stacks of membranes.
Used in the collection, packaging, and distribution of synthesized molecules.
A, P
Secretory Vesicles
Membrane enclosed sacks created at the Golgi complex.
These structures contain cell secretions, like hormones and neurotransmitters. The secretory vesicles are transported to the cell surface where they release those substances outside the cell.
A, P
Lysosomes
Spherical organelles enclosed in a membrane.
Contain digestive enzymes for breaking down old cellular components or ingested food (smaller cells, big macromolecules).
A, P
Vacuoles
Elongated organelles enclosed in a membrane. Few and large in plant cells.
Used to store water and waste products.
A, P
Centrosome
A pair of hollow tubes (the centrioles) surrounded by protein fibers in a star-like arrangement.
Move chromosomes during reproductive division. Plant cells have an equivalent structure to fulfill this function.
A
Peroxisomes
Spherical organelles enclosed in a membrane.
Formed by the endoplasmic reticulum. Converts fats into carbohydrates. Detoxifies potentially harmful oxidants.
A, P
Nucleus
Double membrane structure that encases chromosomes.
Cell structure which directs protein synthesis and cell reproduction.
A, P
Chromatine
Long strands of DNA and protein. During cell division it is packaged into chromosomes.
Stores hereditary (= genetic) information.
A, P
Nucleolus
Aggregations of rRNA and ribosomal proteins.
Area were ribosomes are manufactured.
A, P
Main Human Tissues
Epithelial tissue
Composed of layers of cells that line organ surfaces such as the surface of the skin or the inner lining of the digestive tract. Serves for protection of organs (as in the skin), secretion of substances (when it forms glands - in the skin, in the digestive tract, etc.), and absorption of substances (as in the intestine).
Muscle tissue
Composed of very long cells (up to several cm) called muscle fibres. They have more than one nucleus, are able to expand and contract, and so, are specialized in movements. There are three kinds: cardiac muscle (found in the heart), skeletal muscle (attached to bones) and smooth muscle (not in the heart or attached to bones, as in the stomach).
Nervous tissue
Composed of cells with many projections that are specialized in contacting other cells and transmitting messages via electrical signals.
Connective tissues
Usually specialized in holding together different organs or tissues. It is composed of cells usually very separated by an abundant extracellular matrix. The main types are the bone tissue (in bones), the cartilage tissue (in cartilages), the adipose tissue (as in the fatty layer under the skin - the hypodermis), the fibrous connective tissue (in ligaments and tendons), the loose connective tissue (as in the skin's dermis) and the blood.
Levels of organization
Matter in living beings is organized in a series of levels of increasing complexity, ranging from the atomic level to the multicellular level with tissues and organs. Only plants and animals reach the highest one, whereas bacteria stay at the unicellular level.
Bioelements
The most abundant chemical elements in a livig being, which are not much the same ones that you can find in a rock. The top six are C, H, O, N, P, S, and they're called the primary bioelements.
Biomolecules
The most abundant types of molecules in living beings are always the same ones, no matter if it is a bacterium or a human. They may be organic (with a skeleton of carbon atoms: carbohydrates, lipids, proteins, nucleic acids) or inorganic (without it: water, mineral salts).
Cell
The basic unit of Life. If something is not made up of cells, then it is not a living being. Cells can reproduce and interact with their environment (exchanginng matter and energy, and being able to notice its features). All cells have a plasma membrane, some organelles and genetic material.
Genetic material
In all cells the genetic material is DNA associated to proteins and organized in chromosomes. Bacteria have one chromosome, while humans have 46 in each cell. Its function is to store, express and transmit to the offspring the instructions that tell how every cell and living being will be self-constructed and how will they work.
Prokaryotic / Eukaryotic
Cells without a real nucleus (no nuclear membrane) are the first type. Cells with a real nucleus (genetic material enclosed in a nuclear membrane) are the second type. Bacteria and Archaea are prokayotes; Algae, Protozoa, Fungi, Plants and Animals are eukaryotes.
Mitosis
Cells with more than one chromosome, once they've synthesized a full copy of the whole set of chromosomes, have to carefully organize their division in order to produce two daughter-cells with exactly the same genetic information. Mitosis is the complex process whereby most eukaryotic cells tackle such a task.
Tissues
In multicellular beings there may be different types of cells, each type being specialized in an specific function, and having the specific shape that allows them to fulfill that function the best. Each of those types is called a cellular tissue; examples are the vascular tissue (plants) or the blood tissue (animals). One tissue may have several subtypes of cells (e.g. white blood cells and red blood cells).
Organs / Organ Systems
There are some tasks in a multicellular being that must be achieved by cells of different kinds working together (such as pumping blood throughout the human body). In this case, cells of different tissues gather and make up an organ (epithelial, connective, muscle and adipose cells make up the heart). Several organs working together in a common general task make up an organ system (the heart and the blood vessels make up the circulatory system).
Autotrophs / Heterotrophs
Or Producers and Consumers. The former don't feed off other living beings: they transform inorganic substances to produce the organic substances they need; plants and algae are autotrophs. The latter need to feed on other beings and then transform the organic substances they have eaten into their own organic substances (i.e.: your proteins come partly from the proteins in that beef-steak you ate yesterday); animals, fungi and protozoa are heterotrophs.
Common Structures in Eukaryotic Cells
Description
Function
Where
Cell Wall
Outermost layer on a plant cell composed of cellulose and other complex carbohydrates.
Helps to support and protect the cell.
P
Cell Membrane
Outer layer composed of lipids and proteins.
Controls the permeability of the cell to water and dissolved substances.
A, P
Flagella (flagellum)
Long and scarce threadlike structures that extends from the surface of the cell.
Used for movement of the cell or to move fluids over the cell's surface for absorption.
A
Cilia (cilium)
Short and abundant threadlike structures that extends from the surface of the cell.
Used for movement of the cell or to move fluids over the cell's surface for absorption.
A
Cytoplasm
Semifluid mixture that occupies most of the cell's interior. Contains sugars, aminoacids, and proteins. Also, contains a protein fiber network.
Medium in which organelles and other internal structures exist in. Fiber network support the shape of the cell and anchor organelles to fixed positions.
A, P
Mitochondria (mitochondrion)
Elongated organelles enclosed in a double membrane, the inner one being creased
Sites of respiration: converts sugars and fats into energy through oxidation.
A, P
Chloroplasts
Elongated organelles enclosed in a double membrane and with vesicles containing chlorophyll.
Sites of photosynthesis.
P
Ribosomes
Tiny organelles composed of protein and RNA, not enclosed in a membrane. Often attached to endoplasmic reticulum.
Sites of protein synthesis.
A, P
Endoplasmic Reticulum
Extensive system of internal membranes. May be smooth or rough: the latter has ribosomes attached to its membrane.
Site of transport and synthesis of various cell substances.
A, P
Golgi Complex
Flattened stacks of membranes.
Used in the collection, packaging, and distribution of synthesized molecules.
A, P
Secretory Vesicles
Membrane enclosed sacks created at the Golgi complex.
These structures contain cell secretions, like hormones and neurotransmitters. The secretory vesicles are transported to the cell surface where they release those substances outside the cell.
A, P
Lysosomes
Spherical organelles enclosed in a membrane.
Contain digestive enzymes for breaking down old cellular components or ingested food (smaller cells, big macromolecules).
A, P
Vacuoles
Elongated organelles enclosed in a membrane. Few and large in plant cells.
Used to store water and waste products.
A, P
Centrosome
A pair of hollow tubes (the centrioles) surrounded by protein fibers in a star-like arrangement.
Move chromosomes during reproductive division. Plant cells have an equivalent structure to fulfill this function.
A
Peroxisomes
Spherical organelles enclosed in a membrane.
Formed by the endoplasmic reticulum. Converts fats into carbohydrates. Detoxifies potentially harmful oxidants.
A, P
Nucleus
Double membrane structure that encases chromosomes.
Cell structure which directs protein synthesis and cell reproduction.
A, P
Chromatine
Long strands of DNA and protein. During cell division it is packaged into chromosomes.
Stores hereditary (= genetic) information.
A, P
Nucleolus
Aggregations of rRNA and ribosomal proteins.
Area were ribosomes are manufactured.
A, P
Main Human Tissues
Epithelial tissue
Composed of layers of cells that line organ surfaces such as the surface of the skin or the inner lining of the digestive tract. Serves for protection of organs (as in the skin), secretion of substances (when it forms glands - in the skin, in the digestive tract, etc.), and absorption of substances (as in the intestine).
Muscle tissue
Composed of very long cells (up to several cm) called muscle fibres. They have more than one nucleus, are able to expand and contract, and so, are specialized in movements. There are three kinds: cardiac muscle (found in the heart), skeletal muscle (attached to bones) and smooth muscle (not in the heart or attached to bones, as in the stomach).
Nervous tissue
Composed of cells with many projections that are specialized in contacting other cells and transmitting messages via electrical signals.
Connective tissues
Usually specialized in holding together different organs or tissues. It is composed of cells usually very separated by an abundant extracellular matrix. The main types are the bone tissue (in bones), the cartilage tissue (in cartilages), the adipose tissue (as in the fatty layer under the skin - the hypodermis), the fibrous connective tissue (in ligaments and tendons), the loose connective tissue (as in the skin's dermis) and the blood.
Human Chromosomes
Legend:Representation of the 23 paired chromosomes of the human male.Chromosome: a very long DNA molecule and associated proteins, that carry portions of the hereditary information of an organism.
a. Structure of a chromosome (Typical metaphase chromosome): A chromosome is formed from a single DNA molecule that contains many genes. A chromosomal DNA molecule contains three specific nucleotide sequences which are required for replication: a DNA replication origin; a centromere to attach the DNA to the mitotic spindle.; a telomere located at each end of the linear chromosome. The DNA molecule is highly condensed. The human DNA helix occupy too much space in the cell. Small proteins are responsible for packing the DNA into units called nucleosomes.
b. Stained chromosomes: Chromosomes are stained with A-T (G bands) and G-C (R bands) base pair specific dyes. When they are stained, the mitotic chromosomes have a banded structure that unambiguously identifies each chromosome of a karyotype. Each band contains millions of DNA nucleotide pairs which do not correspond to any functional structure. Adapted from K.F. Jorgenson, J.H. van de Sande, and C.C. Lin, Chromosoma 68:287-302, 1978.
c. Karyotype of a male: The human haploid genome contains 3,000,000,000 DNA nucleotide pairs, divided among twenty two (22) pairs of autosomes and one pair of sex chromosomes.
a. Structure of a chromosome (Typical metaphase chromosome): A chromosome is formed from a single DNA molecule that contains many genes. A chromosomal DNA molecule contains three specific nucleotide sequences which are required for replication: a DNA replication origin; a centromere to attach the DNA to the mitotic spindle.; a telomere located at each end of the linear chromosome. The DNA molecule is highly condensed. The human DNA helix occupy too much space in the cell. Small proteins are responsible for packing the DNA into units called nucleosomes.
b. Stained chromosomes: Chromosomes are stained with A-T (G bands) and G-C (R bands) base pair specific dyes. When they are stained, the mitotic chromosomes have a banded structure that unambiguously identifies each chromosome of a karyotype. Each band contains millions of DNA nucleotide pairs which do not correspond to any functional structure. Adapted from K.F. Jorgenson, J.H. van de Sande, and C.C. Lin, Chromosoma 68:287-302, 1978.
c. Karyotype of a male: The human haploid genome contains 3,000,000,000 DNA nucleotide pairs, divided among twenty two (22) pairs of autosomes and one pair of sex chromosomes.
الخميس، 30 أكتوبر 2008
Tissues
Tissues Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.
Epithelial Tissue - The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body. Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.
Connective Tissue - There are many types of connective tissue in the body. Generally speaking, connective tissue adds support and structure to the body. Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue. In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.
Muscle Tissue - Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement. Examples of muscle tissue are contained in the muscles throughout your body.
Nerve Tissue - Nerve tissue contains two types of cells: neurons and glial cells. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body
Epithelial Tissue - The cells of epithelial tissue pack tightly together and form continuous sheets that serve as linings in different parts of the body. Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are the outer layer of the skin, the inside of the mouth and stomach, and the tissue surrounding the body's organs.
Connective Tissue - There are many types of connective tissue in the body. Generally speaking, connective tissue adds support and structure to the body. Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include the inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue. In addition to these more recognizable forms of connective tissue, blood is also considered a form of connective tissue.
Muscle Tissue - Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement. Examples of muscle tissue are contained in the muscles throughout your body.
Nerve Tissue - Nerve tissue contains two types of cells: neurons and glial cells. Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body
Genetic Disorders
Genetic Disorders
A genetic disorder is a disease that stems from a problem in the genetic makeup of an organism. The abnormality can be a result of heredity, of unexplained genetic mutation or of accidental gene duplication. A majority of the thousands of genetic diseases found in humans happen infrequently. The disorders are broken down into four categories: single gene, multifactorial, chromosomal and mitochondrial.Single gene disorders, also called monogenic, happen when one gene mutates and causes irregular protein functions. Examples are cystic fibrosis (which is the most common), sickle cell anemia, or even color blindness. Multifactorial disorders, also called polygenic, are a more complex combination of larger scale genetic mutation and the effects of lifestyle or environment. This is the most common category of chronic genetic disorder. Examples are diabetes, heart disease and epilepsy. Although these diseases often affect a number of people in the same family, it is not possible to pre-determine who will be afflicted. Chromosomal disorders are caused by abnormalities of the chromosomes in the nucleus of cells, manifested either as a lack, surplus or breakage of the required chromosomal number for proper development. Down Syndrome, for example, is a disease due to surplus. Mitochondrial disorder is the most rare category. It results from the mutation of the nonchromosal DNA of cellular mitochondria.
A genetic disorder is a disease that stems from a problem in the genetic makeup of an organism. The abnormality can be a result of heredity, of unexplained genetic mutation or of accidental gene duplication. A majority of the thousands of genetic diseases found in humans happen infrequently. The disorders are broken down into four categories: single gene, multifactorial, chromosomal and mitochondrial.Single gene disorders, also called monogenic, happen when one gene mutates and causes irregular protein functions. Examples are cystic fibrosis (which is the most common), sickle cell anemia, or even color blindness. Multifactorial disorders, also called polygenic, are a more complex combination of larger scale genetic mutation and the effects of lifestyle or environment. This is the most common category of chronic genetic disorder. Examples are diabetes, heart disease and epilepsy. Although these diseases often affect a number of people in the same family, it is not possible to pre-determine who will be afflicted. Chromosomal disorders are caused by abnormalities of the chromosomes in the nucleus of cells, manifested either as a lack, surplus or breakage of the required chromosomal number for proper development. Down Syndrome, for example, is a disease due to surplus. Mitochondrial disorder is the most rare category. It results from the mutation of the nonchromosal DNA of cellular mitochondria.
nucleus
Nucleus
The nucleus is found in all eukaryotic cells; this membrane-bound structure contains most of the cell's genetic material (excluded material is primarily the DNA found in mitonchondria). The two primary functions of the nucleus are to control cytoplasmic chemical reactions, and to store information necessary for cell division. The nucleus also contains certain proteins that scientists think regulate the expression of genes.The nucleus of a regular eukaryotic cell varies in diameter from 11 to 22.25 micrometers. It's enclosed in a semiporous double membrane that is variously called the nuclear envelope or the nuclear membrane. The outer membrane is attached to the endoplasmic reticulum. The inside of the nuclear membrane is supported by a structure of filaments or microtubules referred to as the nuclear lamina.Inside the nucleus are one or several nucleoli surrounded by the nucleoplasm made up of dissolved nucleotide triphosphates, enzymes, proteins, and transcription factors, and a network of fibers called the nuclear matrix.The DNA of the cell are found inside the nucleus as well, and RNA are transcribed here.
The nucleus is found in all eukaryotic cells; this membrane-bound structure contains most of the cell's genetic material (excluded material is primarily the DNA found in mitonchondria). The two primary functions of the nucleus are to control cytoplasmic chemical reactions, and to store information necessary for cell division. The nucleus also contains certain proteins that scientists think regulate the expression of genes.The nucleus of a regular eukaryotic cell varies in diameter from 11 to 22.25 micrometers. It's enclosed in a semiporous double membrane that is variously called the nuclear envelope or the nuclear membrane. The outer membrane is attached to the endoplasmic reticulum. The inside of the nuclear membrane is supported by a structure of filaments or microtubules referred to as the nuclear lamina.Inside the nucleus are one or several nucleoli surrounded by the nucleoplasm made up of dissolved nucleotide triphosphates, enzymes, proteins, and transcription factors, and a network of fibers called the nuclear matrix.The DNA of the cell are found inside the nucleus as well, and RNA are transcribed here.
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