Information

5.14: Introduction to Organelles - Biology

5.14: Introduction to Organelles - Biology


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

What you’ll learn to do: Identify membrane-bound organelles found in eukaryotic cells

Have you ever heard the phrase “form follows function?” It’s a philosophy practiced in many industries. For example, a skyscraper should be built with several elevator banks; a hospital should be built so that its emergency room is easily accessible.

Our natural world originated the principle of form following function, especially in cell biology, and this will become clear as we explore eukaryotic cells. Unlike prokaryotic cells, eukaryotic cells have:

  1. a membrane-bound nucleus
  2. numerous membrane-bound organelles—such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others
  3. several, rod-shaped chromosomes

Because a eukaryotic cell’s nucleus is surrounded by a membrane, it is often said to have a “true nucleus.” The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.


5.14: Introduction to Organelles - Biology

Have you ever heard the phrase “form follows function?” It’s a philosophy practiced in many industries. In architecture, this means that buildings should be constructed to support the activities that will be carried out inside them. For example, a skyscraper should be built with several elevator banks a hospital should be built so that its emergency room is easily accessible.

Our natural world originated the principle of form following function, especially in cell biology, and this will become clear as we explore eukaryotic cells. Unlike prokaryotic cells, eukaryotic cells have:

  1. a membrane-bound nucleus
  2. numerous membrane-bound organelles—such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others
  3. several, rod-shaped chromosomes

Because a eukaryotic cell’s nucleus is surrounded by a membrane, it is often said to have a “true nucleus.” The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.


Protist movement

Protist Reproduction

Protists have complex life cycles. Many have both asexual and sexual reproduction. An example is a protist called Spirogyra, a type of algae, shown Figure below. It usually exists as haploid cells that reproduce by binary fission. In a stressful environment, such as one that is very dry, Spirogyra may produce tough spores that can withstand harsh conditions. Spores are reproductive cells produced by protists (and other organisms). If two protist spores are close together, they can fuse to form a diploid zygote. This is a type of sexual reproduction. The zygote then undergoes meiosis, producing haploid cells that repeat the cycle.

Protist Nutrition

Protists get food in one of three ways. They may ingest, absorb, or make their own organic molecules.

  • Ingestive protists ingest, or engulf, bacteria and other small particles. They extend their cell wall and cell membrane around the food item, forming a food vacuole. Then enzymes digest the food in the vacuole.
  • Absorptive protists absorb food molecules across their cell membranes. This occurs by diffusion. These protists are important decomposers.
  • Photosynthetic protists use light energy to make food. Protists that are photosynthetic have chloroplasts. Photosynthesis takes place inside the chloroplasts. They are major producers in aquatic ecosystems.

Lesson Summary

  • Kingdom Protista includes all eukaryotes that are not animals, plants, or fungi. It is a very diverse kingdom. It consists of both single-celled and multicellular organisms.
  • Protists have nuclear membranes around their DNA. They also have other membrane-bound organelles. Many live in aquatic habitats, and most are motile, or able to move. Protists have complex life cycles that may include both sexual and asexual reproduction. They get food through ingestion, absorption, or photosynthesis.

Lesson Review Questions

Recall

2. Identify three structures that protists use to move.

3. Describe three ways that protists get food.

Apply Concepts

4. A mystery organism consists of one cell. It could be a protist or a prokaryote. What single fact about the mystery cell would allow you to determine which type of organism it is? Explain your answer.

Think Critically

5. Compare and contrast asexual and sexual reproduction in protists.

Points to Consider

Protists are traditionally classified as animal-like, plant-like, or fungi-like. You will read more about each of these types of protists in the next lesson.


Introduction

The plasma membrane, which is also called the cell membrane, has many functions but, the most basic one is to define the borders and act as gatekeeper for the cell. The plasma membrane is selectively permeable, meaning some molecules can freely enter or leave the cell. Others require help from specialized structures, other molecules, or require energy in order to cross. One example of a molecule that assists other molecules across the plasma membrane is a protein called NPC1. This protein is involved in moving cholesterol and other types of fats across the plasma membrane. Some people have a genetic condition resulting in improperly functioning NPC1. As a result, excessive cholesterol accumulates within cells causing a condition called NPC Disease.

Scientists from the Albert Einstein College of Medicine, Harvard Medical School, and the Whitehead Institute for Biomedical Research discovered that the Ebola virus also uses NPC1 to hitch a ride into cells and replicate. The scientists used mice that lacked the NPC1 protein to test this hypothesis. When the scientists tried to infect these mice with Ebola, none of the mice got sick. Then they tried to infect mice with partially functioning NPC1 and found that they got sick, but did not die. In other words, without properly functioning NPC1, the Ebola virus cannot infect a mouse. If this pattern also exists in humans, it means that anyone with NPC Disease and its subsequent problem with high cholesterol may also be protected from Ebola.

The complete research report can be found here.

Teacher Support

Show students a wilted plant and ask them why the plant has wilted. What is happening on a cellular level regarding movement of molecules? Can the wilting can be reversed?

Plants have cell walls that surround the plasma membrane and prevent cell lysis in a hypotonic solution. The plasma membrane can only expand to the limit of the cell wall, so the cell will not lyse. In fact, the cytoplasm in plants is always slightly hypertonic to the cellular environment and water will always enter a cell if water is available. This inflow of water produces turgor pressure, which stiffens the cell walls of the plant. In non-woody plants, turgor pressure supports the plant. Conversely, if the plant is not watered, the extracellular fluid will become hypertonic, causing water to leave the cell. In this condition, the cell does not shrink because the cell wall is not flexible. However, the cell membrane detaches from the wall and constricts the cytoplasm. This is called plasmolysis. Plants in this condition lose turgor pressure and wilt.

Before students begin this chapter, it is useful to review these concepts: Plasma membranes are the membrane boundary of all cells. Eukaryotic cells have a plasma membrane and intracellular membranes: including: a nuclear membrane and membrane-bound organelles (such as mitochondria). In contrast, prokaryotic cells only have a plasma membrane.

Also, review definitions: intracellular, extracellular, cytosol, and extracellular fluid cell surface to area rations and rates of diffusion.


Biological System of Classification

Q. A non living thing such as a bicycle does not grow. However, a crystal immersed in a saturated solution may increase in size. How is this change different from that of a living organism?

A. In living organisms, the growth is permanent, and is usually due to an increase in cells. The crystal does not contain cells, and the change in size is due to a chemical process which can also be reversed using other chemical processes.

Cells - The smallest unit of life capable of living in an environment free of life.

Nutrition - Process by which organisms take in food and convert it into new protoplasm (living matter).

Respiration - The oxidation of food substances to release energy for cell activities.

Excretion - Removal of metabolic waste products from organism

Locomotion - Ability to move from one place to another

Adaptation - Characteristics of an organism that improves its chances of surviving in its environment.

Reproduction - Biological process by which new individual organisms - offspring - are produced from their parents.

Classification - Group living organisms according to their similarities and differences.

To make the classification of animals easier and more systematic, the biological system of classification was created which groups animals according to different groups (traits they possess). As one goes down the order of classification similarities between different species increase. The diagram is shown on the right.

Binominal System - Created by Carlous Linnaeus, Latin is used to give two names to each species. The first name refers to the genus (always starts with a capital letter), and the second name refers to the name of the species (always starts with a small letter).

Felis domestica (Domestic Cat)

Through this it can be seen that the tiger and lion are different species but come from the same genus. The lion and tiger belong to the same family of the domestic cat, 'felidae'.


Cell Organelles

Hello there, my DNA
Inside the nucleus, you are contained
You send signals to the Ribosome
Which makes up proteins, encoded by genes

Contained in membranes, they’re your cell personnel
They work as a team to serve the cell well,
You gotta love’em they’re your cell organelles

Proteins are sent via vesicles
In and out, and all around the cell
Vesicles sent by the Rough ER
Go down the smooth, to the Golgi Body

Contained in membranes, they’re your cell personnel
They work as a team to serve the cell well,
You gotta love ’em they’re your cell organelles

Chloroplasts make sugars in plants,
and the Mitochondria is the power plant
The Cytoskeleton gives it its shape,
while the cytoplasm fills it up like a grape

Contained in membranes, they’re your cell personnel
They work as a team to serve the cell well,
You gotta love ’em they’re your cell organelles

Re-writing lyrics

Next, I used half sheets containing two lines of lyrics, and distributed them to pairs of students. Students worked together to re write their two lyrics into their own words.

When everyone was finished we compiled everyone’s answer into a word document. One column had the lyrics to the song, and one column had the student-friendly translation. Copies were then given to each student.


Cell Fractionation: Extraction, Homogenization and Centrifugation

Cell fractionation is a procedure for rupturing cells, separation and suspension of cell constituents in isotonic medium in order to study their structure, chemical composition and function.

Cell fractionation involves 3 steps: Extraction, Homogenization and Centrifugation.

1. Extraction:

It is the first step toward isolating any sub-cellular structures. In order to maintain the biological activity of organelles and bio-molecules, they must be extracted in mild conditions called cell-free systems. For these, the cells or tissues are suspended in a solution of appropriate pH and salt content, usually isotonic sucrose (0.25 mol/L) at0-40°C.

2. Homogenization:

The suspended cells are then disrupted by the process of homogenization.

It is usually done by:

(ii) High Pressure (French Press or Nitrogen Bomb),

(iv) Sonication (ultrasonic vibrations). Grinding is done by pestle and mortar or potter homogenizer (a high-speed blender). The later consists of two cylinders separated by a narrow gap.

The shearing force produced by the movement of cylinders causes the rupture of ceils. Ultrasonic waves are produced by piezoelectric crystal. They are transmitted to a steel rod placed in the suspension containing cells. Ultrasonic waves produce vibrations which rupture the cells. The liquid containing suspension of cell organelles and ether constituents is called homogenate. Sugar or sucrose solution preserves the cell organelles and prevents their clumping.

3. Centrifugation:

The separation (fractionation) of various components of the homogenate is carried out by a series of cemrifugations in an instrument called preparative ultracentrifuge. The ultracentrifuge has a metal rotor containing cylindrical holes to accommodate centrifuge tubes and a motor that spin the rotor at high speed to generate centrifugal forces. Theodor Svedberg (1926) first developed die ultracentrifuge which he used to estimate the molecular weight of hemoglobin.

Present day ultracentrifuge rotate at speeds up to 80,000 rpm (rpm= rotations per minute) and generates a gravitational pull of about 500,000 g, so that even small molecules like t-RNA, enzymes can sediment and separate from other components. The chamber of ultracentrifuge is kept in a high vacuum to reduce friction, prevent heating and maintain the sample at 0-4°C.

During centrifugation, the rate at which each component settle down depends on its size and shape and described in terms of sedimentation coefficient or Svedberg unit or S-value, where IS = 1 x 10- 13 second.

The standard cell fractionation technique involves following methods:

(a) Differential velocity centrifugation [Velocity sedimentation or Rate zonal centrifugation):

It is the first step of cell fractionation by which various sub-cellular organelles are separated based on differences in their size. The homogenate in first filtered to remove unbroken cell clumps and collected in a centrifuge tube. The filtered homogenate when centrifuged in a series of steps at successively greater speeds, each step yields a pellet and a supernatant

The supernant of each step is removed to a fresh tube for centrifugation. For instance, at low speed (600g. for: 10 min) nuclear fraction or pellet will sediment at medium speed (15,000g x 5 min) mitochondria fraction sediment and at high speed (80,000 g. x 5 min.) micro-somal fraction sediment. The final supernant is soluble fraction or cytosol.

(b) Equilibrium Density-gradient centrifugation (Equilibrium sedimentation):

The organelle fractions (pallets) obtained in velocity centrifugation is purified by equilibrium density-gradient centrifugation. In this method organelles are separated by their density not by their size.

The impure organelle fraction is layered on the top of a gradient solution, e.g., sucrose solution or glycerol solution. The solution is more concentrated (dense) at the bottom of the centrifuge tube, and decreases in concentration gradually towards the top. The tube when centrifuged at high speed the various organelles migrate to an equilibrium position where their density is equal to the density of the medium. Meselson, Stahl and Vinograd (1957) used denser cesium chloride gradient for separation of a heavy DNA with 15 N from DNA with 14 N to provide evidence for semi-conservative DNA replication.

In conclusion, we may say that what one can learn about cells, depends on the tools at one’s disposed and, in fact, major advances in cell biology have frequently taken place with the introduction of new too is and techniques to the study of cell. Thus, to gain different types of information regarding cell, cell biologists have developed and employed various instruments and techniques. A basic knowledge of some of these methods is earnestly required.


Calibration of microscopes to measure cell organelles Part 2

  • Steps ⌲ Decide on which magnification you want to use. Then try to align the stage micrometer with the ocular micrometer as shown below using the same magnification.
  • Calculations ⌲ The stage micrometer total length will be = (unit length*) X (total # of divisions within the 2 meeting points). Once you get the total length (L), then your calculation of what is a unit length of the ocular ruler will be ⌲ (L) / (the total # divisions within the aligned 2 points). This will give you a unit length of the ocular ruler at the particular magnification that you used. * will be made known to you.
  • Future ⌲ So every time you use this magnification, you just need to line the sample in the ocular ruler and then count the # of divisions and multiply by the calculated unit length you derived earlier.


Watch the video: 1ο Θέμα Επανάληψης Βιολογίας Γ Γυμνασίου 1ο Κεφάλαιο (July 2022).


Comments:

  1. Leof

    Yes, the problem described in the post has existed for a long time. But who will decide it?

  2. Jakome

    I think you are wrong. I can prove it. Write to me in PM, we will handle it.

  3. Atmore

    We are sorry that they interfere… But they are very close to the theme.



Write a message