3: Cell Structure and Function

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This chapter outlines the discovery of cells and cell theory. It identifies ways in which all cells are alike and ways in which they vary. The chapter describes in detail important cell structures and their functions; and it explains how cells obtain energy, grow, and divide.

3.1: Case Study- The Importance of Cells
We all get tired sometimes, especially if we have been doing a lot of physical activity like these hikers. But for Jasmin, a 34 year old former high school track star who is now a recreational runner, his tiredness was going far beyond what he thought should be normal for someone who is generally in good physical shape.
3.2: Discovery of Cells and Cell Theory
Cells are the basic units of the structure and function of living things. All organisms are made up of one or more cells, and all cells have many of the same structures and carry out the same basic life processes.
3.3: Variation in Cells
Although all living cells have certain things in common, different types of cells, even within the same organism, may have their unique structures and functions. Cells with different functions generally have different shapes that suit them for their particular job.
3.4: Plasma Membrane
The plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. The membrane protects and supports the cell and controls everything that enters and leaves it.
3.5: Cytoplasm and Cytoskeleton
The cytoplasm is a thick, usually colorless solution that fills each cell and is enclosed by the cell membrane. Sometimes cytoplasm acts like a watery solution, and sometimes it takes on a more gel-like consistency. A framework of protein scaffolds called the cytoskeleton provides the cytoplasm and the cell with structure.
3.6: Cell Organelles
An organelle is a structure within the cytoplasm of a eukaryotic cell that is enclosed within a membrane and performs a specific job. Organelles in animal cells include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, vesicles, and vacuoles.
3.7: Cell Transport
If a cell were a house, the plasma membrane would be walls with windows and doors. Moving things in and out of the cell is an important role of the plasma membrane. It controls everything that enters and leaves the cell. There are two basic ways that substances can cross the plasma membrane: passive transport, which requires no energy; and active transport, which requires energy.
3.8: Active Transport and Homeostasis
When substances require energy to cross a plasma membrane often because they are moving from an area of a lower concentration to an area of a higher concentration, the process is called active transport.
3.9: Cellular Respiration
Energy is required to break down and build up molecules and to transport many molecules across plasma membranes. A lot of energy is lost to the environment as heat. The story of life is a story of energy flow - its capture, its change of form, its use for work, and its loss as heat. The cells of living things power their activities with the energy-carrying molecule ATP. The cells of most living things make ATP from glucose in the process of cellular respiration. This process occurs in three sta
3.10: Fermentation
An important way of making ATP without oxygen is fermentation. Fermentation starts with glycolysis, which does not require oxygen, but it does not involve the latter two stages of aerobic cellular respiration (the Krebs cycle and electron transport). There are two types of fermentation, called alcoholic fermentation and lactic acid fermentation.
3.11: Case Study Conclusion- Tired and Chapter Summary
Jasmin discovered that his extreme fatigue, muscle pain, vision problems, and vomiting were due to issues in his mitochondria, an organelle. Mitochondria create energy for the cells of the body.
3.12: DNA and RNA
This young person has naturally red hair. Why is this hair red instead of some other color? And, in general, what causes specific traits to occur? There is a molecule in human beings and most other living things that is largely responsible for their traits. The molecule is large and has a spiral structure in eukaryotes. What molecule is it? With these hints, you probably know that the molecule is DNA.
3.13: Chromosomes and Genes
Chromosomes are coiled structures made of DNA and proteins. Chromosomes are encoded with genetic instructions for making proteins. These instructions are organized into units called genes. Most genes contain the instructions for a single protein. There may be hundreds or even thousands of genes on a single chromosome.
3.14: Protein Synthesis
Your DNA, or deoxyribonucleic acid, contains the genes that determine who you are. How can this organic molecule control your characteristics? DNA contains instructions for all the proteins your body makes. Proteins, in turn, determine the structure and function of all your cells. What determines a protein's structure? It begins with the sequence of amino acids that make up the protein. Instructions for making proteins with the correct sequence of amino acids are encoded in DNA.
3.15: Genetic Code
The genetic code consists of the sequence of nitrogen bases in a polynucleotide chain of DNA or RNA. The bases are adenine (A), cytosine (C), guanine (G), and thymine (T) (or uracil, U, in RNA). The four bases make up the "letters" of the genetic code. The letters are combined in groups of three to form code "words," called codons. Each codon stands for (encodes) one amino acid, unless it codes for a start or stop signal. There are 20 common amino acids in proteins.
3.16: Mutations
Mutations are random changes in the sequence of bases in DNA or RNA. The word mutation may make you think of Ninja Turtles, but that's a misrepresentation of how most mutations work. First of all, everyone has mutations. In fact, most people have dozens or even hundreds of mutations in their DNA. Secondly, from an evolutionary perspective, mutations are essential. They are needed for evolution to occur because they are the ultimate source of all new genetic variation in any species.
3.17: Regulation of Gene Expression
Using a gene to make a protein is called gene expression. It includes the synthesis of the protein by the processes of transcription of DNA and translation of mRNA. It may also include further processing of the protein after synthesis. Gene expression is regulated to ensure that the correct proteins are made when and where they are needed. Regulation may occur at any point in the expression of a gene.
3.18: The Human Genome
The human genome refers to all the DNA of the human species. Human DNA consists of 3.3 billion base pairs and is divided into more than 20,000 genes on 23 pairs of chromosomes. The human genome also includes noncoding sequences (e.g. intergenic region) of DNA.
3.19: Case Study Conclusion- Parmacogenomics and Chapter Summary
Arya asked their doctor about Pharmacogenomics. The doctor explains to Arya that Pharmacogenomics is the tailoring of drug treatments to people's genetic makeup, a form of 'personalized medicine'.
3.20: Case Study- Genetic Similarities and Differences
This introduces the concept of mitosis and meiosis in the form of a Leukemia case study.
3.21: Cell Cycle and Cell Division
Cell division is the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells. How this happens depends on whether the cell is prokaryotic or eukaryotic. Cell division is simpler in prokaryotes than eukaryotes because prokaryotic cells themselves are simpler. Prokaryotic cells have a single circular chromosome, no nucleus, and few other organelles. Eukaryotic cells, in contrast, have multiple chromosomes contained within a nucleus.
3.22: Mitotic Phase - Mitosis and Cytokinesis
The process in which the nucleus of a eukaryotic cell divides is called mitosis. During mitosis, the two sister chromatids that make up each chromosome separate from each other and move to opposite poles of the cell. This is shown in the figure below. Mitosis actually occurs in four phases: prophase, metaphase, anaphase, and telophase.
3.23: Mutations and Cancer
Your cells may grow and divide without performing their necessary functions, or without fully replicating their DNA, or without copying their organelles. Probably not much good could come of that. So the cell cycle needs to be highly regulated and tightly controlled. And it is.
3.24: Sexual Reproduction- Meiosis and gametogenesis
Whereas asexual reproduction produces genetically identical clones, sexual reproduction produces genetically diverse individuals. Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. As both parents contribute half of the new organism's genetic material, the offspring will have traits of both parents, but will not be exactly like either parent.
3.25: Genetic Variation
Genetic variation. It is this variation that is the essence of evolution. Without genetic differences among individuals, "survival of the fittest" would not be likely. Either all survive, or all perish.
3.26: Mitosis vs. Meiosis and Disorders
Both mitosis and meiosis result in eukaryotic cells dividing. So what is the difference between mitosis and meiosis? The primary difference is the differing goals of each process. The goal of mitosis is to produce two daughter cells that are genetically identical to the parent cell, meaning the new cells have exactly the same DNA as the parent cell. Mitosis happens when you want to grow, for example. You want all your new cells to have the same DNA as the previous cells.
3.27: Case Study Conclusion- Genes and Chapter Summary
Humans are much more genetically similar to each other than they are different.