ClassX Video Lessons The genes you don’t get from your parents (but can’t live without) – Devin Shuman
Inside each of our cells lies a second set of genes, distinct from the 23 pairs of chromosomes we inherit from our parents. This is a universal truth for nearly all multicellular organisms, including animals, plants, and fungi. These genes belong to our mitochondria, a unique organelle within our cells. Mitochondria are not entirely part of us, yet they are not separate either. So, what makes them so different from everything else in our bodies?
About 1.5 billion years ago, scientists believe that a single-celled organism engulfed the ancestor of mitochondria, leading to the evolution of all multicellular life forms. Mitochondria play a crucial role in our cells by converting the energy from the food we eat and the oxygen we breathe into ATP, a form of energy our cells can use. Without ATP, our cells would not survive.
Humans have over 200 types of cells, and all, except mature red blood cells, contain mitochondria. Red blood cells are unique because their primary function is to transport oxygen, which mitochondria would otherwise consume. Mitochondria use oxygen and metabolites to generate energy and possess their own DNA. Interestingly, mitochondrial DNA varies significantly across species. For instance, mammals typically have 37 mitochondrial genes, while some plants like cucumbers can have up to 65, and certain fungi have only one. Some microbes in low-oxygen environments are even losing their mitochondria, with one group, oxymonad monocercomonoides, having already done so.
Mitochondria continue to evolve alongside and independently from the organisms that house them. In most species, mitochondrial DNA is inherited from a single parent, usually the mother in humans and most animals. Sperm cells contain a small number of mitochondria to aid in swimming, but these are discarded after fertilization. In contrast, an egg contains thousands of mitochondria, each with multiple copies of mitochondrial DNA. This results in over 150,000 copies of mitochondrial DNA inherited from the mother, each potentially slightly different from the others.
As a fertilized egg develops, the mitochondria are distributed among the cells of the growing embryo. By the time tissues and organs form, variations in mitochondrial DNA are randomly scattered throughout the body. Mitochondria have their own replication process, separate from the cell’s division. They undergo fusion and division, isolating faulty DNA or malfunctioning mitochondria for removal.
This dynamic process means that the mitochondrial DNA you inherit at birth can change throughout your life and within your body. Mitochondria are dynamic and somewhat independent, yet they are influenced by their environment—us. It is believed that some mitochondrial genes were transferred to the host’s genome long ago. Today, mitochondria, although having their own genome, rely on instructions from our DNA to replicate. While mitochondrial DNA is inherited from one parent, the genes responsible for building and regulating mitochondria come from both parents.
Mitochondria continue to challenge simple classification. Their story unfolds within each of our cells, both separate and inseparable from us. Understanding them better can provide valuable insights into protecting human health and unraveling more about our evolutionary history.
Embark on a virtual tour of a cell to explore the role of mitochondria. Use an interactive simulation to visualize how mitochondria convert food and oxygen into ATP. Reflect on how this process is crucial for cellular function and survival.
Participate in a debate about the evolutionary origins of mitochondria. Research the endosymbiotic theory and discuss its implications for understanding multicellular life. Consider how this ancient event continues to influence modern biology.
Conduct a comparative analysis of mitochondrial DNA across different species. Examine the number of mitochondrial genes in mammals, plants, and fungi. Discuss how these differences might relate to the organisms’ environments and evolutionary paths.
Analyze a case study on mitochondrial inheritance patterns. Investigate how mitochondrial DNA is passed from mother to offspring and the implications for genetic diversity. Discuss the potential for mitochondrial diseases and their inheritance.
Create an artistic representation of mitochondria and their dynamic nature. Use any medium—drawing, painting, digital art—to express the concept of mitochondria as both separate and integral to our cells. Share your work and explain your artistic choices.
Here’s a sanitized version of the provided YouTube transcript:
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Inside our cells, each of us has a second set of genes completely separate from the 23 pairs of chromosomes we inherit from our parents. This is true for every animal, plant, fungus, and nearly every multicellular organism on Earth. This second genome belongs to our mitochondria, an organelle inside our cells. They are not fully a part of us, but they are not separate either—so why are they so different from anything else in our bodies?
Approximately 1.5 billion years ago, scientists believe a single-celled organism engulfed the ancestor of mitochondria, creating the predecessor of all multicellular organisms. Mitochondria play an essential role: they convert energy from the food we eat and the oxygen we breathe into a form of energy our cells can use, known as ATP. Without this energy, our cells begin to die.
Humans have over 200 types of cells, and all except mature red blood cells contain mitochondria. This is because a red blood cell’s job is to transport oxygen, which mitochondria would consume before it could reach its destination. All mitochondria use oxygen and metabolites to create energy and have their own DNA, but mitochondrial DNA varies more across species than other types of DNA. In mammals, mitochondria typically have 37 genes. In some plants, like cucumbers, mitochondria can have up to 65 genes, while some fungal mitochondria have only 1. A few microbes that live in oxygen-poor environments appear to be on the path to losing their mitochondria entirely, and one group, oxymonad monocercomonoides, has already done so.
This variety exists because mitochondria are still evolving, both in tandem with the organisms that contain them and separately, on their own timeline. To understand how that’s possible, it helps to take a closer look at what the mitochondria inside us are doing, starting from the moment we are conceived. In almost all species, mitochondrial DNA is passed down from only one parent. In humans and most animals, that parent is the mother. Sperm contain approximately 50 to 75 mitochondria in the tail to help them swim, but these dissolve with the tail after conception. Meanwhile, an egg contains thousands of mitochondria, each with multiple copies of mitochondrial DNA. This results in over 150,000 copies of mitochondrial DNA that we inherit from our mothers, each of which is independent and may vary slightly from the others.
As a fertilized egg grows and divides, those thousands of mitochondria are distributed into the cells of the developing embryo. By the time we have differentiated tissues and organs, variations in the mitochondrial DNA are scattered randomly throughout our bodies. To make matters even more complex, mitochondria have a separate replication process from our cells. As our cells replicate by dividing, mitochondria end up in new cells, and they are also fusing and dividing themselves on their own timeline. As mitochondria combine and separate, they sequester faulty DNA or mitochondria that aren’t functioning properly for removal.
All this means that the random selection of your mother’s mitochondrial DNA that you inherit at birth can change throughout your life and throughout your body. So, mitochondria are dynamic and, to a degree, independent, but they are also shaped by their environments: us. It is believed that long ago, some of their genes were transferred to their host’s genomes. Today, although mitochondria have their own genome and replicate separately from the cells that contain them, they cannot do this without instruction from our DNA. And though mitochondrial DNA is inherited from one parent, the genes involved in building and regulating the mitochondria come from both.
Mitochondria continue to defy tidy classification. Their story is still unfolding inside each of our cells, simultaneously separate and inseparable from our own. Learning more about them can provide us with tools to protect human health in the future and teach us more about our history.
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This version maintains the original content while ensuring clarity and coherence.
Genes – Segments of DNA that contain the instructions for the development, functioning, growth, and reproduction of organisms. – The study of genes has provided significant insights into the genetic disorders that affect human health.
Mitochondria – Organelles within eukaryotic cells that generate most of the cell’s supply of adenosine triphosphate (ATP), used as a source of chemical energy. – Mitochondria are often referred to as the powerhouses of the cell due to their role in energy production.
DNA – Deoxyribonucleic acid, a molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. – DNA sequencing has revolutionized the field of genomics by allowing scientists to read the genetic code of organisms.
Evolution – The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. – Charles Darwin’s theory of evolution by natural selection explains how species adapt to their environments over time.
Cells – The basic structural, functional, and biological units of all living organisms, often called the building blocks of life. – The discovery of cells was a pivotal moment in biology, leading to the development of cell theory.
Energy – The capacity to do work, which in biological systems is often derived from the metabolism of nutrients. – Photosynthesis in plants is a process that converts light energy into chemical energy stored in glucose molecules.
Organisms – Individual living entities that can react to stimuli, reproduce, grow, and maintain homeostasis. – Microorganisms play a crucial role in ecosystems by decomposing organic material and recycling nutrients.
Inheritance – The process by which genetic information is passed on from parent to offspring. – Mendel’s experiments with pea plants laid the foundation for our understanding of genetic inheritance.
Reproduction – The biological process by which new individual organisms are produced from their parents. – Sexual reproduction involves the combination of genetic material from two parents, leading to genetic diversity in offspring.
Environment – The external conditions, resources, stimuli, etc., with which an organism interacts. – An organism’s ability to adapt to its environment is crucial for its survival and reproduction.
