Name: how prokaryotes survive without a nucleus
Uploaded: 2023-04-30T10:29:03.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.4

Prokaryotic Cells

פרוקריוטים כוללים ארכאונים וחיידקים, אורגניזמים חד-תאיים פשוטים חסרי אברונים הקשורים לממברנה.
אורגניזמים אלה מוקפים בקרום פלזמה חדיר באופן סלקטיבי התוחם רכיבים תאיים, תלוי בחופשיות בציטופלסמה צמיגה.
מלבד קרום הפלזמה, לתאי חיידקים יש רמה נוספת של הגנה בצורה של דופן תא המסייעת לשמור על צורתם הכללית ולחץ אוסמוטי פנימי.
דופן התא מורכבת מפפטידוגליקן – פולימר של חומצות אמינו וסוכרים.
לחלק מהחיידקים יש שכבת הגנה נוספת שנקראת קפסולה – שכבה רב-סוכרית שמקדמת היצמדות תאים למשטחים.
בתוך התא, דנ"א חד-גדילי דו-גדילי מקובץ באזור מרכזי שנקרא נוקלאואיד, שם הוא יכול לתקשר עם חלבונים שצפים בחופשיות.
לרוב החיידקים יש גם פיסות דנ"א עגולות שצפות בחופשיות, שנקראות פלסמידים, שיכולות להשתכפל באופן עצמאי ולהעניק יתרונות הישרדותיים כמו עמידות לאנטיביוטיקה.
זני חיידקים מסוימים עשויים להכיל חלבון ספציפי ואברונים הקשורים לשומנים עם פונקציות שונות.
לדוגמה, ציאנובקטריה מכילים קרבוקסיזומים ותילקואידים לקצירת אנרגיית אור לביצוע פוטוסינתזה.

תאים פרוקריוטיים

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פרוקריוטים הם אורגניזמים חד-תאיים קטנים הכוללים את התחומים - ארכאונים וחיידקים. חיידקים כוללים מיקרואורגניזמים נפוצים רבים, כמו סלמונלה ו-E. coli, בעוד שהארכאונים כוללים אקסטרמופילים החיים בסביבות קשות, כמו מעיינות געשיים.

בדומה לתאים איקריוטים, כל התאים הפרוקריוטים מוקפים בממברנת פלזמה, יש להם חומר גנטי בצורה של DNA בודד ועגול, ציטופלזמה שממלאת את פנים התא וריבוזומים המסנתזים חלבונים. עם זאת, בניגוד לתאים איקריוטים, לפרוקריוטים חסר גרעין או אברונים תוך-תאיים אחרים הקשורים לממברנה. הרכיבים התאיים שלהם צפים בחופשיות בתוך הציטופלזמה, למרות שה-DNA שלהם מקובץ בתוך אזור הנקרא נוקלואיד.

בתוך הציטופלזמה, לפרוקריוטים רבים יש פיסות DNA קטנות, מעגליות דו-גדיליות הנקראות פלסמידים. אלה נבדלים מה-DNA הכרומוזומלי של התא ונושאים רק כמה גנים מיוחדים המספקים לחיידקים יתרונות הישרדותיים, כמו עמידות לאנטיביוטיקה. פלסמידים משכפלים את עצמם ויכולים להיות מועברים בין תאים פרוקריוטיים.

לרוב החיידקים יש דופן תא העשוי מפפטידוגליקן שנמצא מחוץ לממברנת הפלזמה שלהם. הוא מגן פיזית על התא ועוזר לו לשמור על לחץ אוסמוטי בסביבות שונות. לחיידקים רבים יש גם שכבת קפסולה דביקה המכסה את דופן התא שלהם ומאפשרת להם להיצמד למצע או זה לזה, ובכך מספקת הגנה נוספת.

בעוד שלחיידקים אין אברונים הקשורים לקרום, לחלקם יש פיתולים של קרום הפלזמה שמבצעים פונקציות מיוחדות - כמו פוטוסינתזה בציאנובקטריה. לכן, למרות שהפרוקריוטים הם תאים פשוטים בהשוואה לאאוקריוטים, יש להם כמה מבנים ייחודיים שעוזרים להם לבצע פונקציות מורכבות ומאפשרים להם לחיות במגוון רחב של סביבות.

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פרוקריוטים הם אורגניזמים חד-תאיים קטנים הכוללים את התחומים – ארכיאה וחיידקים. חיידקים כוללים מיקרואורגניזמים נפוצים רבים, כגון ...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Cells, Genomes, and Evolution

תאים, גנומים ואבולוציה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

how prokaryotes survive without a nucleus

Prokaryotes are small unicellular organisms that live without a nucleus. They include the domains Archaea and Bacteria. Bacteria include common microbes such as Salmonella and E. coli, while Archaea include extremophiles that live in harsh places like volcanic springs.

Prokaryotic cells still share several basic features with eukaryotic cells. They have a plasma membrane, cytoplasm, ribosomes, and genetic material in the form of single, circular DNA. Their cell parts float freely in the cytoplasm because they do not have membrane-bound intracellular organelles.

Their DNA is clustered in a region called the nucleoid. Many prokaryotes also carry plasmids, which are small, circular, double-stranded DNA molecules. Plasmids are separate from chromosomal DNA and can carry genes that give survival advantages, such as antibiotic resistance. They can also self-replicate and move between prokaryotic cells.

Most bacteria have a cell wall made of peptidoglycan outside the plasma membrane. This wall helps protect the cell and supports osmotic pressure in different environments. Many bacteria also have a sticky capsule that covers the wall and helps them attach to surfaces or to other cells. Some bacteria even have infoldings of the plasma membrane for special jobs, such as photosynthesis in cyanobacteria.

How Prokaryotes Survive Without a Nucleus

how-prokaryotes-survive-without-a-nucleus

what are cells?

Cells as the Building Blocks of Life

Cells are the basic building blocks of life. A bacterium can be a single cell, while a human is made of trillions of cells. Even with this range, cells share key features that support life. A living cell has a plasma membrane. This is a bilayer of lipids that separates the cytoplasm inside the cell from the outside environment. A cell also carries genetic information in the form of DNA. In prokaryotic cells, DNA is found in a region called the nucleoid. In eukaryotic cells, DNA is enclosed...

the tree of life - bacteria, archaea, and eukaryotes

the-tree-of-life-bacteria-archaea-and-eukaryotes

Three Domains on the Tree of Life

The tree of life shows how living things are grouped into three domains: Bacteria, Archaea, and Eukaryotes. This classification helps explain the major branches of life and how they are related. Bacteria and Archaea are both single-celled organisms, but they are not the same. Eukaryotes include organisms with more complex cells, such as plants, animals, and fungi. Together, these three domains give a broad picture of life on Earth. Understanding the tree of life helps students compare cell...

prokaryotic cells

Prokaryotes are small unicellular organisms that live without a nucleus. They include the domains Archaea and Bacteria. Bacteria include common microbes such as Salmonella and E. coli, while Archaea include extremophiles that live in harsh places like volcanic springs. Prokaryotic cells still share several basic features with eukaryotic cells. They have a plasma membrane, cytoplasm, ribosomes, and genetic material in the form of single, circular DNA. Their cell parts float freely in the...

eukaryotic compartmentalization

How Organelles Keep Cells Working

Eukaryotic cells keep their organelles separate so each part can do a specific job. Organelles such as the nucleus and mitochondria are surrounded by membranes. These membranes are selectively permeable, which means they control what enters and leaves. That control creates small internal environments with conditions suited to each organelle. These controlled spaces help organelles work more efficiently. In animal cells, lysosomes keep an acidic environment that helps their enzymes digest...

eukaryotic evolution

How Eukaryotic Cells Became Complex

Eukaryotic cells became complex through a debated evolutionary path that likely involved endosymbiosis. The most accepted model is the endosymbiont theory, which explains how organelles such as mitochondria and chloroplasts may have entered an ancestral cell. Other ideas include the nucleus-first hypothesis, the mitochondria-first hypothesis, and the eukaryote-first hypothesis. The nucleus-first hypothesis says an ancestral prokaryote first formed a membrane around its DNA, creating the...

animal and plant cell structure

Plant vs Animal Cell Division and Specialization

Plant and animal cells differ in how they divide, organize into tissues, and specialize for different jobs. Both cell types divide by mitosis in non-gametic cells and by meiosis in gametic cells, but the details are not the same. These differences help explain how each cell type supports growth and reproduction. During cell division, animal cells use centrosomes to organize spindle fibers and separate chromosomes. Plant cells do not have centrosomes. Instead, they use a microtubule-organizing...

cytoplasm

Cytoplasm and the Cell’s Internal Support

The cytoplasm is the cell’s internal space that holds organelles and the cytoskeleton. It is suspended in the cytosol, an aqueous fluid made of water, ions, salts, and many organic molecules. This fluid helps keep the cell organized and supports many cellular activities. The cytoplasm is also where protein synthesis and protein folding take place. The watery cytosol helps proteins fold correctly. In a folded protein, hydrophobic amino acid side chains tend to stay buried in the core, while...

the nucleus

Nuclear DNA, Chromatin, and Nucleoli

The nucleus is a membrane-bound organelle that stores chromosomal DNA and helps control what proteins a eukaryotic cell makes. It acts as the cell’s control center. DNA in mitochondria and chloroplasts is different because it mainly supports functions specific to those organelles. Inside the nucleus, DNA is wrapped around proteins called histones. This DNA-protein complex is called chromatin. During interphase, when the cell is not dividing, chromatin stays loosely arranged so the DNA is easy...

the dna helix

How DNA Structure Was Discovered

DNA is the genetic material that passes traits from one generation to the next in organisms and most viruses. It is made of two strands of nucleotides that twist into a spring-like double helix. The shape is not perfectly even. It also has repeating grooves called the major groove and the minor groove. The major groove forms where the sugar-phosphate backbones are farther apart. This wider space gives DNA-binding proteins, including transcription factors, better access to the bases. The minor...

the central dogma

DNA to Protein: RNA’s Role

DNA to protein flow depends on RNA as the link between genetic information and the amino acids that build proteins. Early scientists knew that DNA stores the information for cell functions and that proteins carry out most of those functions. For a long time, they did not know how the code in DNA became a working protein. At first, many people thought one gene was changed directly into its protein. Two findings in eukaryotic cells challenged that idea. Protein production does not happen in the...

mutations

Mutations in DNA and Inherited Disease

Mutations are changes in the DNA sequence. They can happen on their own during DNA copying, or they can be caused by environmental factors. Scientists describe mutations in several ways, including whether they change the amino acid sequence of a protein, how much DNA they affect, and whether they occur in somatic cells or germline cells. Some mutations are point mutations. A point mutation changes a single nucleotide in DNA. Other mutations are chromosomal alterations, which change the number...

genome size and the evolution of new genes

genome-size-and-the-evolution-of-new-genes

Genome Size and Gene Evolution

Genome size and gene evolution are linked through changes in DNA sequence and genome structure. Some genes can arise from parts of the genome that were not coding before, while others come from changes to existing genes. These shifts help explain how new genetic material can appear over time. A genome is the full set of DNA in an organism. Its size can change as DNA is added, removed, or rearranged. The transcript highlights that genome size is not fixed, and that these changes can shape the...

gene families

Shared Origins of Gene Families

Gene families are groups of related genes that share a common origin. They form when genes are copied and then change over time. These related genes can be found within the same genome. The video also connects gene families to homologous genes and orthologous genes. Homologous genes are genes with a shared evolutionary origin. Orthologous genes are homologous genes found in different species. Gene families help show how these relationships are used to study evolution and related gene functions.

gene evolution - fast or slow?

Gene Evolution Rates and Selection

Gene evolution can happen at different rates, and natural selection helps shape those changes. Some genes change slowly because important DNA changes are removed over time. Other genes can change more quickly when different mutations are kept in a population. The rate of evolution depends on how a gene is used and how strongly it is affected by selection. Genes with essential jobs often stay more similar across species. Genes under weaker pressure may show more variation and may evolve faster.<br...

types of genetic transfer between organisms

types-of-genetic-transfer-between-organisms

Vertical and Horizontal Gene Transfer

Genetic transfer between organisms happens in two main ways: vertical gene transfer and horizontal gene transfer. These two routes explain how hereditary material moves from one generation to the next or between organisms that are not parent and offspring. Vertical gene transfer passes genes from parent to offspring during reproduction. This is the usual way genetic information is inherited in living things. Horizontal gene transfer moves genetic material between organisms outside of...

key terms and concepts

Learn how prokaryotes survive without a nucleus, from circular DNA and plasmids to peptidoglycan cell walls, capsules, and specialized membrane folds.

How Prokaryotes Survive Without a Nucleus | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Louisiana Student Standards for Science

High School

Life Sciences

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance And Variation Of Traits

HS-LS3-1

Tennessee Academic Standards

From Molecules to Organisms: Structures and Processes

BIO1.LS1.1

BIO1.LS1.2

Virginia  Standards of Learning

HIgh School

BIO.3

BIO.3.b

BIO.6

BIO.6.a

Life Science

LS.3

LS.3.b

Florida Department of Education

SC.912.L.15

SC.912.L.15.6

Georgia Standards of Excellence

SB4.a

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LS.Bio.1.1

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introduction-to-mechanisms-of-enzyme-catalysis

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Ribozymes

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LS.Bio.1.2

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Prokaryotes are small unicellular organisms that include the domains&#x2014;Archaea and Bacteria. Bacteria include many common organisms, such as ...

Cytoplasm

The cytoplasm consists of organelles and a framework of protein scaffolds called the cytoskeleton suspended in an aqueous solution, the cytosol. The ...

The Nucleus

The nucleus is a membrane-bound organelle that acts as a control center in a eukaryotic cell. It contains chromosomal DNA, which controls gene expression ...

Endoplasmic Reticulum

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Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Golgi Apparatus

As they leave the Endoplasmic Reticulum (ER), properly folded and assembled proteins are selectively packaged into vesicles. These vesicles are ...

Lysosomes

Lysosomes are membrane-enclosed spherical sacs derived from the Golgi apparatus. The most important function of the lysosome is degrading macromolecules ...

Peroxisomes

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The Extracellular Matrix

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Use models to explain how the structure of organelles determines its function and supports overall cell processes.

LS.Bio.1.3

Analyze how the relationship between structure and function supports life processes within organisms.

How Prokaryotes Survive Without a Nucleus

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