3.1: Cell Structure and Function - Biology

3.1: Cell Structure and Function - Biology

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  • 3.1.1: How Cells Are Studied
    In multicellular organisms, several cells of one particular kind interconnect with each other and perform shared functions to form tissues (for example, muscle tissue, connective tissue, and nervous tissue), several tissues combine to form an organ (for example, stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems functioning together form an organism (such as an elephant, for example).
  • 3.1.2: Comparing Prokaryotic and Eukaryotic Cells
    Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro- = before; -karyon- = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes (eu- = true).
  • 3.1.3: Eukaryotic Cells
    At this point, it should be clear that eukaryotic cells have a more complex structure than do prokaryotic cells. Organelles allow for various functions to occur in the cell at the same time. Before discussing the functions of organelles within a eukaryotic cell, let us first examine two important components of the cell: the plasma membrane and the cytoplasm.
  • 3.1.4: The Cell Membrane
    The plasma membrane is referred to as the fluid mosaic model and is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane. These function to identify other cells.
  • 3.1.5: Passive Transport
    The most direct forms of membrane transport are passive. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement. In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion. A physical space in which there is a different concentration of a single substance is said to have a concentration gradient.
  • 3.1.6: Active Transport
    Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient, that is, if the concentration of the substance inside the cell must be greater than its concentration in the extracellular fluid, the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight material, such as ions, through the membrane.

Thumbnail: A diagram of a typical prokaryotic cell. (Public Domain; LadyofHats).

Biology 3. Cell - Structure & Functions 3 1 Cells The Unit Of Life Notes for NEET 2021 PDF in Detailed and Precise Manner

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Function of a Centriole

Cells form a complex endoskeleton of microtubules which allows substances to be transported to any location in a cell. Products are tagged with special glycoproteins (sugar and protein) which act as signals to specific motor proteins. These proteins attach to the product, or vesicle that the product is stored in, and also attach to a microtubule. Microtubules are arranged at the centriole, of which each centrosome has two. The centrioles anchor the microtubules that extend from it and contain the factors needed to create more tubules.

During mitosis, centrosomes are replicated by duplicating each centriole. The 4 centrioles then divide into two centrosomes, each with one centriole at a right angle to the second centriole. Microtubules extend between the centrosomes which push the sets of centrioles apart. The centrioles will be pushed apart, to opposite ends of the cell. Once established, each centriole will then extend microtubules into the cytoplasm that seek out chromosomes. The microtubules attach to the chromosomes at their centromeres, which are parts of the DNA specially formulated to allow the attachment of special proteins and microtubules. The microtubules are then disassembled from the centriole, which draws the microtubule back toward the centriole, as motor proteins pull the chromosomes apart.

The cell biology of systemic insulin function

Insulin is the paramount anabolic hormone, promoting carbon energy deposition in the body. Its synthesis, quality control, delivery, and action are exquisitely regulated by highly orchestrated intracellular mechanisms in different organs or "stations" of its bodily journey. In this Beyond the Cell review, we focus on these five stages of the journey of insulin through the body and the captivating cell biology that underlies the interaction of insulin with each organ. We first analyze insulin's biosynthesis in and export from the β-cells of the pancreas. Next, we focus on its first pass and partial clearance in the liver with its temporality and periodicity linked to secretion. Continuing the journey, we briefly describe insulin's action on the blood vasculature and its still-debated mechanisms of exit from the capillary beds. Once in the parenchymal interstitium of muscle and adipose tissue, insulin promotes glucose uptake into myofibers and adipocytes, and we elaborate on the intricate signaling and vesicle traffic mechanisms that underlie this fundamental function. Finally, we touch upon the renal degradation of insulin to end its action. Cellular discernment of insulin's availability and action should prove critical to understanding its pivotal physiological functions and how their failure leads to diabetes.

AP® Biology - Part 1: The Cell

Preparing for the AP Biology exam requires a deep understanding of many different topics in biology as well as an understanding of the format of the AP exam and the types of questions it asks. This course is Part 1 of our AP Biology series designed to prepare you for the AP Biology exam.

In Part 1, you will learn about the cell, its structure, its functions, and the chemistry that drives all of the processes cells carry out on a daily basis.

As you work through this course, you will find lecture videos taught by expert AP Biology teachers, practice multiple choice questions and free response questions that are similar to what you will encounter on the AP exam and tutorial videos that show you step-by-step how to solve problems. By the end of the course, you will be prepared to take on the AP exam!

This course is authorized as an Advanced Placement® (AP®) course by the AP Course Audit. The AP Course Audit was created by the College Board to give schools and students the confidence that all AP courses meet or exceed the same clearly articulated curricular expectations of colleges and universities.

By taking an AP course and scoring successfully on the related AP Exam, students can:

  • Stand Out in College Admissions
  • Earn College Credits
  • Skip Introductory Classes
  • Build College Skills

Advanced Placement® and AP® are trademarks registered and/or owned by the College Board, which was not involved in the production of, and does not endorse, these offerings.

For more information about cells:

The National Institute of General Medical Sciences has a science education booklet about cells called Inside the Cell.

The National Human Genome Research Institute's Talking Glossary provides a definition of a cell as well as an illustration and video.

The Genetic Science Learning Center at the University of Utah offers an interactive introduction to cells and their many functions.

Queen Mary University of London allows you to explore a 3-D cell and its parts.

Structure and function of ER membrane contact sites with other organelles

The endoplasmic reticulum (ER) is the largest organelle in the cell, and its functions have been studied for decades. The past several years have provided novel insights into the existence of distinct domains between the ER and other organelles, known as membrane contact sites (MCSs). At these contact sites, organelle membranes are closely apposed and tethered, but do not fuse. Here, various protein complexes can work in concert to perform specialized functions such as binding, sensing and transferring molecules, as well as engaging in organelle biogenesis and dynamics. This Review describes the structure and functions of MCSs, primarily focusing on contacts of the ER with mitochondria and endosomes.

Conflict of interest statement

statement The authors declare no competing interests.


Figure 1. Structure of endoplasmic reticulum (ER)…

Figure 1. Structure of endoplasmic reticulum (ER) membrane-contact sites (MCSs)

Figure 2. Dynamics of endoplasmic reticulum (ER)…

Figure 2. Dynamics of endoplasmic reticulum (ER) membrane contact sites (MCSs)

Figure 3. Endoplasmic reticulum (ER) membrane contact…

Figure 3. Endoplasmic reticulum (ER) membrane contact sites (MCSs) function in lipid biosynthesis and exchange

Figure 4. Calcium (Ca 2+ ) exchange…

Figure 4. Calcium (Ca 2+ ) exchange at endoplasmic reticulum (ER) membrane contact sites (MCSs)

60–500 μM). In the extracellular space, [Ca 2+ ] is high (

1mM) compared to the intracellular cytosol (

100nM). Newly formed endosomes have taken up Ca 2+ from the extracellular space, so the luminal [Ca 2+ ] is close to the same as that of the extracellular space (

1 mM). Luminal Ca 2+ is then released so that early endosomes have [Ca 2+ ]

0.5 μM and late endosomes have [Ca 2+ ]

2.5 μM. The ER–endosome MCS is a site of dynamic Ca 2+ crosstalk. Endosomes may be able to sequester Ca 2+ released from the ER. The ER transfers Ca 2+ to mitochondria, with peak mitochondrial Ca 2+ concentrations reaching 100 μM. b | ER Ca 2+ released from the ER through inositol-1,4,5- trisphosphate receptors (Ins(1,4,5)P3Rs) provides a concentrated Ca 2+ spike that can be taken up through the outer mitochondrial membrane (OMM) by VDACs (voltage dependent anion channels) and then through the inner mitochondrial membrane (IMM) by the mitochondrial Ca 2+ uniporter (MCU) ion transporter into the mitochondrial matrix. The 75 kDa glucose-regulated protein (GRP75) functions as a chaperone, coupling Ins(1,4,5)P3R to the VDACs. c | Endosomes are capable of releasing Ca 2+ though transient receptor potential channels (TRPs) or two-pore channels (TPCs). ER Ca 2+ released from ER via Ins(1,4,5)P3Rs could be taken up into endosomes through unknown endosome Ca 2+ -uptake channels. Ca 2+ release from endosomes can also stimulate Ca 2+ release from the ER through Ins(1,4,5)P3Rs and vice versa.

Figure 5. Endoplasmic reticulum (ER) membrane contact…

Figure 5. Endoplasmic reticulum (ER) membrane contact sites (MCSs) define the timing and position of…

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A cell is a structural and functional unit of life. A microscope is required to study cell structure. Scientist Robert Hook First studied the cell structure in the year 1665 using a self designed microscope. A cell having following Structure and Function of cell Organelles.

Major Cell organelles are as follows
1.Cell Membrane- Cell membrane enclose the cell and regulates the in and out flow of substance. It is also known as plasma membrane which form the covering of animal cell. It is elastic, living, double layer and permeable membrane. It is made up of protein and lipid molecules.

Function-It regulated movement of molecules inside and outside the cell.

2. Cell Wall – The outer layer in the plant cell is called cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose and chitin. Cellulose is a complex substance and provides structural strength to plant.

Function-When a living plant cell loses water through osmosis the is shrinkage or contraction of the contents of the cell away from the cell wall.

3. Protoplasm –The whole fluid present inside plasma membrane is protoplasm. Protoplasm is made up of various chemical substance like water ,ions, salt and organic molecule .it is the living pat of cell. Protoplasm is divided into two parts.
i) Cytoplasm – The fluid found outside the nuclear membrane.
ii) Nucleoplasm – The fluid found inside the nuclear membrane.
4. Nucleus- It is the most important organelle of a cell and usually lies in the center. It may lie in the periphery. Its basic function is cell division and multiplication. The nucleus has a double layered covering called nuclear membrane. The nucleus contains chromosomes .chromosome contain information for inheritance of features form parents to next generation in the form of DNA ( Deoxyribo Nucleic Acid) molecules.

Function- It controls all activity of cells. So it is also known as “control room “of cell. Chromatin transmits hereditary characters from parent of their offspring.

5. Mitochondria– Discovered by Altman in the year 1886.these are cylindrical rod shaped or spherical structure found in cytoplasm. It is surrounded by double layered membrane. Inner membrane has many fold called cristae. The fluid present inside mitochondria is called matrix, which contain many enzyme and co-enzyme.

Function- Mitochondria is the respiratory site of cellular respiration. Mitochondria synthesize energy rich compound ATP (Adenosine Triphopshate) ATP is known as the energy currency of the cell. Mitochondria are known as the Powerhouse of the cell.

6. Golgi Bodies-Golgi bodies are made up of group of tubes, vesicles and vacuoles. These are also called as Golgi apparatus. Golgi apparatus discovered by scientist Camilo Golgi.

Function- It functions include the storage, processing modification and packaging of products in vesicles. It also involved in the synthesis of cell wall, plasma membrane and lysosomes.

7. Ribosome- Discovered by Palade. Small granules like structure found attached to the endoplasmic reticulum or in Free State. It is made up of ribonucleic acid (RNA).

Function- Ribosome helps in protein Synthesis.

8. Lysosomes – Lysosomes are like structure bounded by single membrane and contain hydrolytic enzyme. These enzymes made by RER. Lysosomes discovered by De Duve.

Function- it helps in intercellular digestion. The enzyme found in lysosomes may digest the entire ell. Therefore lysosomes also known as the “suicide bags “ of a cell.

9. Endoplasmic Reticulum (ER)- the endoplasmic reticulum (ER) is a large network of tubules like structure found in cytoplasm .it is attached with the nucleus on one side and on other side it is joined with plasma membrane . There are two types of ER-
i ) Rough Endoplasmic reticulum (RER)- Rough endoplasmic reticulum looks rough under a microscope because it has particles called ribosome attached to its surface.

Function- RER concerned with protein synthesis and transport. RER developed in protein exporting cells (ex. pancreatic cells and Liver) .

ii ) Smooth Endoplasmic reticulum (SER) – Smooth endoplasmic reticulum looks smooth under a microscope because it has free ribosome particles .its surface.

Function- Smooth Endoplasmic reticulum helps in synthesizes and transports lipids and steroids. Some kinds of smooth E. R transport proteins from the rough E. R. And still other kinds break down energy rich glycogen and fats.

Function- Endoplasmic reticulum (ER) helps in the distribution of material. It forms supporting framework of cell.
10. Plastids- Plastids are present only in plant cells. There are three types of plastids-
i) Chromoplast (colored plastids) –It provides various colors to the plant.
ii) Chloroplasts– Plastids containing the pigment chlorophyll are known as chloroplast. Chloroplasts are important for photosynthesis in plants. It known as “kitchen of the cell”.
iii) Leucoplast (white or colorless plastids) – Leucoplasts are primarily organelles. It stores the food in the form of starch, fat and protein.
11. Centrosome– it is Located in the cytoplast adjacent to the nucleus and takes part in cell division.
12. Vacuoles- Vacuoles are storage sacs for solid or liquid contents .vacuoles are small sized in animal cells while plant cells have very large vacuoles.
Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids and some proteins.

Function- it helps in osmoregulation .It stores toxic metabolic waste.

4.1: Cell Structure and Function

A cell is the smallest living thing in the human organism, and all living structures in the human body are made of cells. There are hundreds of different types of cells in the human body, which vary in shape (e.g. round, flat, long and thin, short and thick) and size (e.g. small granule cells of the cerebellum in the brain (4 micrometers), up to the huge oocytes (eggs) produced in the female reproductive organs (100 micrometers) and function. However, all cells have three main parts, the plasma membrane, the cytoplasm and the nucleus. The plasma membrane (often called the cell membrane) is a thin flexible barrier that separates the inside of the cell from the environment outside the cell and regulates what can pass in and out of the cell. Internally, the cell is divided into the cytoplasm and the nucleus. The cytoplasm (cyto- = cell -plasm = &ldquosomething molded&rdquo) is where most functions of the cell are carried out. It looks a bit-like mixed fruit jelly, where the watery jelly is called the cytosol and the different fruits in it are called organelles. The cytosol also contains many molecules and ions involved in cell functions. Different organelles also perform different cell functions and many are also separated from the cytosol by membranes. The largest organelle, the nucleus is separated from the cytoplasm by a nuclear envelope (membrane). It contains the DNA (genes) that code for proteins necessary for the cell to function.

Generally speaking, the inside environment of a cell is called the intracellular fluid (ICF), (intra- = within referred to all fluid contained in cytosol, organelles and nucleus) while the environment outside a cell is called the extracellular fluid (ECF) (extra- = outside of referred to all fluid outside cells). Plasma, the fluid part of blood, is the only ECF compartment that links all cells in the body.

Figure (PageIndex<1>) 3-D representation of a simple human cell. The top half of the cell volume was removed. Number 1 shows the nucleus, numbers 3 to 13 show different organelles immersed in the cytosol, and number 14 on the surface of the cell shows the plasma membrane

Concepts, terms, and facts check

Study Questions Write your answer in a sentence form (do not answer using loose words)

1. What is a cell?
2. What is a plasma membrane?
3. What is a cytoplasm?
4. What is the intracellular fluid (ICF)?
5. What is the extracellular fluid (ECF)?

The plasma (cell) membrane separates the inner environment of a cell from the extracellular fluid. It is composed of a fluid phospholipid bilayer (two layers of phospholipids) as shown in figure (PageIndex<2>) below, and other molecules. Not many substances can cross the phospholipid bilayer, so it serves to separate the inside of the cell from the extracellular fluid. Other molecules found in the membrane include cholesterol, proteins, glycolipids and glycoproteins, some of which are shown in figure (PageIndex<3>) below. Cholesterol, a type of lipid, makes the membrane a little stronger. Different proteins found either crossing the bilayer (integral proteins) or on its surface (peripheral proteins) have many important functions. Channel and transporter (carrier) proteins regulate the movement of specific molecules and ions in and out of cells. Receptor proteins in the membrane initiate changes in cell activity by binding and responding to chemical signals, such as hormones (like a lock and key). Other proteins include those that act as structural anchors to bind neighboring cells and enzymes. Glycoproteins and glycolipids in the membrane act as identification markers or labels on the extracellular surface of the membrane. Thus, the plasma membrane has many functions and works as both a gateway and a selective barrier.

Figure (PageIndex<2>) Phospholipids form the basic structure of a cell membrane. Hydrophobic tails of phospholipids are facing the core of the membrane, avoiding contact with the inner and outer watery environment. Hydrophilic heads are facing the surface of the membrane in contact with intracellular fluid and extracellular fluid.

Figure (PageIndex<3>) Small area of the plasma membrane showing lipids (phospholipids and cholesterol), different proteins, glycolipids and glycoproteins.

Concepts, terms, and facts check

Study Questions Write your answer in a sentence form (do not answer using loose words)

1. What is the function of the cell membrane?
2. Which are the three types of biomolecules that form the cell membrane?

Almost all human cells contain a nucleus where DNA, the genetic material that ultimately controls all cell processes, is found. The nucleus is the largest cellular organelle, and the only one visible using a light microscope. Much like the cytoplasm of a cell is enclosed by a plasma membrane, the nucleus is surrounded by a nuclear envelope that separates the contents of the nucleus from the contents of the cytoplasm. Nuclear pores in the envelope are small holes that control which ions and molecules (for example, proteins and RNA) can move in and out the nucleus. In addition to DNA, the nucleus contains many nuclear proteins. Together DNA and these proteins are called chromatin. A region inside the nucleus called the nucleolus is related to the production of RNA molecules needed to transmit and express the information coded in DNA. See all these structures below in figure (PageIndex<4>).

Figure (PageIndex<4>) Nucleus of a human cell. Find DNA, nuclear envelope, nucleolus, and nuclear pores. The figure also shows how the outer layer of the nuclear envelope continues as rough endoplasmic reticulum, which will be discussed in the next learning objective.

Concepts, terms, and facts check

Study Questions Write your answer in a sentence form (do not answer using loose words)

1. What is the nuclear envelope?
2. What is a nuclear pore?
3. What is the function of the nucleus?

An organelle is any structure inside a cell that carries out a metabolic function. The cytoplasm contains many different organelles, each with a specialized function. (The nucleus discussed above is the largest cellular organelle but is not considered part of the cytoplasm). Many organelles are cellular compartments separated from the cytosol by one or more membranes very similar in structure to the cell membrane, while others such as centrioles and free ribosomes do not have a membrane. See figure (PageIndex<5>) and table (PageIndex<1>) below to learn the structure and functions of different organelles such as mitochondria (which are specialized to produce cellular energy in the form of ATP) and ribosomes (which synthesize the proteins necessary for the cell to function). Membranes of the rough and smooth endoplasmic reticulum form a network of interconnected tubes inside of cells that are continuous with the nuclear envelope. These organelles are also connected to the Golgi apparatus and the plasma membrane by means of vesicles. Different cells contain different amounts of different organelles depending on their function. For example, muscle cells contain many mitochondria while cells in the pancreas that make digestive enzymes contain many ribosomes and secretory vesicles.

Figure (PageIndex<5>) Typical example of a cell containing the primary organelles and internal structures. Table (PageIndex<1>) below describes the functions of mitochondrion, rough and smooth endoplasmic reticulum, Golgi apparatus, secretory vesicles, peroxisomes, lysosomes, microtubules and microfilaments (fibers of the cytoskeleton)

(shown here synthesizing a protein)

Found attached to RER and free in the cytosol

Fibers of the Cytoskeleton

(a) microtubule made of tubulin,

(b) microfilament made of actin, and

(c) intermediate fibers made of keratins

(found in an area in the cell called centrosome)

Concepts, terms, and facts check

Study Questions Write your answer in a sentence form (do not answer using loose words)

1. What is an organelle?
2. Which are the organelles listed in the module?

Watch the video: Νευρικό Σύστημα. Μέρος Α: Δομή και Λειτουργία Νευρικών Κυττάρων. (May 2022).