Name: how eukaryotic cells became complex
Uploaded: 2023-04-30T10:29:18.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance And Variation Of Traits

HS-LS3-1

Eukaryotic Evolution

La première cellule eucaryote est issue d’une cellule procaryote primitive, dont le matériel génétique était librement regroupé dans le cytoplasme.
Ces cellules étaient entourées d’une membrane plasmique, mais ne contenaient aucun organite lié à la membrane.
Au fur et à mesure de l’évolution de la cellule, la membrane plasmique s’est invaginée et pincée, donnant naissance à des corps ou organites intracellulaires enfermés dans une membrane, tels que le réticulum endoplasmique ou RE.
L’ER s’est ensuite organisée pour former l’enveloppe nucléaire autour de l’amas d’ADN.
De plus, le RE a bourgeonné de grappes vésiculaires qui ont fusionné pour former l’appareil de Golgi.
Selon la théorie de l’endosymbiote, cette cellule ancestrale a ensuite englouti un petit procaryote aérobie.
Cette bactérie échappait à la digestion et permettait à la cellule hôte d’utiliser l’oxygène et de générer de l’énergie. Il a finalement évolué vers les mitochondries - la centrale électrique des cellules eucaryotes existantes.
En temps voulu, certaines de ces cellules eucaryotes ancestrales ont acquis des endosymbiontes supplémentaires comme les cyanobactéries, un groupe de bactéries capables de photosynthèse.
Ces endosymbiontes ont ensuite évolué en chloroplastes, site de photosynthèse chez les algues vertes et les plantes.

<ol>
	<li>Archibald, John M. « Endosymbiose et évolution des cellules eucaryotes. » Current Biology 25, n° 19 (2015) : R911-R921.</li>
	<li>Mariscal, Carlos et W Ford Doolittle. « Les eucaryotes d’abord : comment cela pourrait-il être ? Transactions philosophiques de la Royal Society de Londres. Série B, Sciences biologiques vol. 370,1678 (2015) : 20140322.</li>
</ol>

Évolution des eucaryotes

La théorie des endosymbiotes est la théorie la plus largement acceptée de l'évolution des eucaryotes ; cependant, sa progression est encore quelque peu débattue. Selon l’hypothèse du noyau d’abord, le procaryote ancestral a d’abord développé une membrane pour enfermer l’ADN et former le noyau. À l’inverse, l’hypothèse des mitochondries d’abord suggère que le noyau s’est formé après une endosymbiose des mitochondries.

Contrairement à la théorie des endosymbiotes, l'hypothèse des eucaryotes d'abord propose que les formes de vie procaryotes et archéennes les plus simples aient évolué à partir des cellules eucaryotes complexes déjà existantes.

Preuve de La Théorie des Endosymbiotes

Les preuves de la théorie des endosymbiotes proviennent des nombreuses similitudes que les organites eucaryotes, comme les mitochondries et les chloroplastes, partagent avec les cellules procaryotes. Comme les cellules procaryotes, les mitochondries et les chloroplastes contiennent des génomes circulaires double brin dépourvus d’histones. Ces organites se divisent également par le processus de fission, semblable à la division cellulaire bactérienne, plutôt que par mitose. Parmi les deux membranes qui les entourent, les membranes internes ressemblent à la membrane plasmique bactérienne en termes de composition lipidique et protéique. Enfin, la structure des gènes, le code génétique et la machinerie traductionnelle (telle que les ribosomes) de ces organites ressemblent davantage à la machinerie procaryote qu'à la machinerie eucaryote.

LECA - Dernier Ancêtre commun Eucaryote

On pense que tous les eucaryotes ont évolué à partir du dernier ancêtre commun eucaryote ou LECA il y a environ 1 100 à 2 300 millions d’années. On pense que LECA avait déjà acquis des endosymbiotes comme les mitochondries et les chloroplastes à ce stade. Les nouveaux organites ont rendu ces cellules ancestrales plus efficaces et plus puissantes, ce qui leur a permis de développer de nouvelles caractéristiques telles que la multicellularité et la spécialisation cellulaire. Leur grande taille cellulaire et leur compartimentation interne ont également permis à leur génome d’augmenter en taille au cours de l’évolution. Cependant, seule une petite partie de ce génome codait pour des protéines ; la majeure partie était constituée d'ADN non codant, principalement impliqué dans les processus de régulation. La capacité d’activer et de désactiver les gènes lorsque cela est nécessaire était la clé de la spécialisation cellulaire et de la réponse aux changements environnementaux. Des études phylogénétiques et génomiques comparatives montrent cinq à six supergroupes eucaryotes qui ont évolué à partir de LECA et ont ensuite divergé pour former la pléthore de formes de vie que nous voyons aujourd'hui.

Évolution des Eucaryotes

La théorie de l’endosymbiote est la théorie la plus largement acceptée de l’évolution eucaryote ; Cependant, sa progression est encore quelque peu débattue. Selon le ...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Cells, Genomes, and Evolution

Cellules, génomes et évolution

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 nucleus. The mitochondria-first hypothesis proposes that mitochondria were acquired by endosymbiosis before the nucleus formed. The eukaryote-first hypothesis takes a different view and suggests that simpler prokaryotic and archaeal life forms evolved from already existing complex eukaryotic cells.

Several features support the endosymbiont theory. Mitochondria and chloroplasts have circular, double-stranded genomes without histones, which is similar to prokaryotic DNA. They also divide by fission, just like bacterial cells, instead of by mitosis. Their two surrounding membranes also provide clues, because the inner membrane is similar to the bacterial plasma membrane in lipid and protein makeup.

Their genes, genetic code, and translational machinery also look more prokaryotic than eukaryotic. This includes ribosomes, which help build proteins. These shared traits make mitochondria and chloroplasts strong evidence for an endosymbiotic origin.

All eukaryotes are thought to descend from the Last Eukaryotic Common Ancestor, or LECA, which lived about 1100 to 2300 million years ago. By that stage, LECA is believed to have already acquired endosymbionts such as mitochondria and chloroplasts. These new organelles likely made ancestral cells more efficient and powerful.

That extra power may have helped eukaryotes evolve multicellularity and cellular specialization. Their large cell size and internal compartmentalization also allowed genomes to grow during evolution. Most of that added DNA did not code for proteins; instead, it was non-coding DNA involved mainly in regulation. Being able to switch genes on and off when needed helped cells specialize and respond to environmental change. Phylogenetic and comparative genomic studies suggest five to six eukaryotic supergroups later diverged from LECA and gave rise to the diversity of eukaryotic life seen today.

How Eukaryotic Cells Became Complex

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

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...

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

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

Explore how eukaryotic cells evolved through endosymbiosis, LECA, mitochondria, chloroplasts, and the main hypotheses behind eukaryotic complexity.

How Eukaryotic Cells Became Complex | JoVE K12

cell biology

JoVE Core Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

Tennessee Academic Standards

Biology

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

From Molecules to Organisms: Structures and Processes

BIO1.LS1.2

Virginia  Standards of Learning

HIgh School

Life Science

LS.3

LS.3.b

Next Generation Science Standards

Earth and Space Science

Earth’s Systems

HS-ESS2-6

Florida Department of Education

SC.912.L.14

SC.912.L.14.1

SC.912.L.14.5

SC.912.L.15

SC.912.L.15.6

Texas Essential Knowledge and Skills

BIO.5

BIO.5.B

new-york-state-science-learning-standards

New York State Science Learning Standards

Earth and Space Sciences

HS-ESS2-7.

Georgia Standards of Excellence

9-12

SB4.a

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium, or trillions of them, ...

The Tree of Life - Bacteria, Archaea, and Eukaryotes

Prokaryotic Cells

Prokaryotes are small unicellular organisms that include the domains &#8212; Archaea and Bacteria. Bacteria include many common microorganisms, such as ...

Eukaryotic Compartmentalization

One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles, such as the nucleus and mitochondria, that carry ...

The endosymbiont theory is the most widely accepted theory of eukaryotic evolution; however, its progression is still somewhat debated. According to the ...

Animal and Plant Cell Structure

Animal and plant cells not only differ in their structure, function, and mode of nutrition but also in how they reproduce, specialize, and organize into ...

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 ...

The DNA Helix

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most viruses. DNA ...

The Central Dogma

The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
RNA is the Missing Link Between ...

DNA Packaging

DNA as a Genetic Template

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The ...

Organization of Genes

Chromosome Structure

A functional eukaryotic chromosome must contain three elements: a centromere, telomeres, and numerous origins of replication.
The centromere is a DNA ...

Chromosome Replication

Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone ...

The Nucleosome

DNA in a human cell is almost 2m long and it is packed inside a tiny nucleus that is only a few microns in diameter. The level of compaction of DNA inside ...

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of ...

Nucleosome Remodeling

Nucleosomes are the basic units of chromatin compaction. Each nucleosome consists of the DNA bound tightly around a histone core, which makes the DNA ...

Chromatin Packaging

Each human somatic cell contains 6 billion base-pairs of DNA. Each base-pair is 0.34 nm long, which means that each diploid cell contains a staggering 2 ...

Karyotyping

Histone Modification

The histone proteins have a flexible N-terminal tail extending out from the nucleosome. These histone tails are often subjected to post-translational ...

Spreading of Chromatin Modifications

The histone&#160;proteins in the nucleosomes are post-translationally modified (PTM) to increase or decrease access to DNA. The commonly observed PTMs are ...

Histone Variants at the Centromere

Histone variants are the histone proteins with structural and sequence variations. These variants may be regarded as &#8220;mutant&#8221; forms that ...

Inheritance of Chromatin Structures

Epigenetics is the study of inherited changes in a cell&#39;s phenotype without changing the DNA sequences. It provides a form of memory for the ...

Euchromatin

The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions ...

Heterochromatin

chromatin-position-affects-gene-expression

Chromatin Position Affects Gene Expression

Chromatin is the massive complex of DNA and proteins packaged inside the nucleus. The complexity of chromatin folding and how it is packaged inside the ...

Punnett Squares

Monohybrid Crosses

Dihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel&#8217;s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A ...

Law of Independent Assortment

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an ...

Pedigree Analysis

Multiple Allele Traits

Incomplete Dominance

Gregor Mendel&#39;s work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid ...

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cu&#233;not discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is ...

Polygenic Traits

background-and-environment-affect-phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as ...

Formulate, refine, and evaluate questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. Emphasis should be on traits including completely dominant, codominant, incompletely dominant, and sex-linked traits (e.g., pedigrees, karyotypes, genetic disorders, Punnett squares). Examples do not need to include dihybrid crosses.

X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 ...

The Y Chromosome Determines Maleness

The Y chromosome is a sex chromosome&#160;found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human ...

The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined ...

X-linked Traits

Sex Linked Disorders

Dosage Compensation

In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one ...

X-inactivation

What is Meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

Meiosis I

Meiosis II

Meiosis vs. Mitosis

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to ...

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This ...

Make and defend a claim based on evidence that inheritable genetic variations may result from: (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors. Emphasis is on using data to support arguments for the way variation occurs. Claims should not include the phases of meiosis or the biochemical mechanisms of specific steps in the process.

HS-LS3-2

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations ...

Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population. Emphasis is on distribution and variation of traits in a population and the use of mathematics (e.g., calculations of frequencies in Punnett squares, graphical representations) to describe the distribution.

HS-LS3-3

How Eukaryotic Cells Became Complex

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