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Chapter 7. Cell Structure and Function. Life is cellular. One of the first people to use a microscope to study nature was Anton van Leeuwenhoek . English physicist Robert Hooke is credited with the name “cells” while using a light microscope
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Chapter 7 Cell Structure and Function
Life is cellular • One of the first people to use a microscope to study nature was Anton van Leeuwenhoek. • English physicist Robert Hooke is credited with the name “cells” while using a light microscope • Scientists Schleidenand Schwann are credited with the early parts of the Cell Theory.
The Cell Theory The Cell Theory states the following: • All living things are composed of cells. • Cells are the basic units of structure and function in living things. • New cells are produced from existing cells.
Basic Cell Structures • All cells have a cell membrane and cytoplasm • The cell membrane is a thin, flexible barrier around the cell. • Many cells, especially plants, have a strong layer around the cell membrane known as the cell wall. • The large structure that contains the cell’s genetic material and controls the cell’s activities is called the nucleus. Not all cells contain a nucleus.
Cell Membrane • The cell membrane allows some materials to pass through while keeping other stuff out. It is said to be selectively permeable. • Most of the molecules in the cell membrane are lipids. • The type of lipid that makes up the cell membrane is a phospholipid. • The phospholipids are arranged in a lipid bilayer
Cell Membrane • A phospholipid has a hydrophilic (water-loving) head and hydrophobic (water-hating) tails. • The phospholipids are arranged so their heads point outward and their tails point inward.
Cell Membrane • The cell membrane regulates what enters and leaves the cell, and also provides protection and support. • The cell membrane is made of: • Lipids – the cell membrane is a double-layered sheet called the lipid bilayer • Proteins - protein molecules run through the lipid bilayer and are on the top and bottom surfaces of the membrane
Cell Membrane Proteins • Some of the proteins are on the top and bottom surface of the cell membrane. • These proteins are receptors that transmit chemical signals to the inside of the cell. • Other proteins run all the way through the membrane and create channels for material to pass through. • These proteins are called transport proteins.
Cell Membrane • Carbohydrates – form chains that are attached to the outer surface of the proteins • Act like chemical identification cards, allowing cells to identify each other.
Cell Membrane • Cholesterol ( a steroid which is a lipid) is located in the cell membrane. • It helps keep the phospholipids from sticking together. • Cholesterol helps maintain the fluid nature of the cell membrane.
Fluid Mosaic Model • Together, the phospholipids create a “sea” in which other molecules can float. • The phospholipids can move sideways.
Fluid Mosaic Model • Other components of the membrane, like proteins, can also move along the phospholipids. • Because there are different substances in the cell membrane, a pattern, or mosaic, is created on the surface. • This model of the cell membrane is known at the Fluid Mosaic Model • Components of the cell membrane are in constant motion.
Basic Cell Structures • The material inside the cell membrane – but not including the nucleus – is called the cytoplasm.
Prokaryotes and Eukaryotes Cells are divided into two categories: • prokaryotes- have a cell membrane and cytoplasm but do not contain a nucleus. • All bacteria are prokaryotes • eukaryotes – contain a nucleus, cell membrane, cytoplasm, and organelles – structures that perform specialized functions within the cell • All plants, animals, and fungi, and many microorganisms are eukaryotes.
Prokaryotes and Eukaryotes • Some organisms are made of only one cell; they are called unicellular. • Organisms of many cells are called multicellular.
Cell Structures What’s in a cell? Well, that depends on what kind of cell you are talking about. • Plants, algae fungi and nearly all prokaryotes have a cell wall • The main function of the cell wall is to provide support and protection for the cell. • Animal cells do not have a cell wall.
Nucleus • Eukaryotes (including plants and animals) have a nucleus. • The nucleus is the “brains” of the cell. It controls most of the cell processes and contains the hereditary information of DNA.
Nucleus The nucleus includes: • chromatin – contains genetic information (where the DNA is). Condenses to form chromosomes during cell division. • nucleolus - believed to be where the assembly of ribosomes begins • nuclear envelope – a double-membrane layer that surrounds the nucleus and keeps the DNA inside.
Cytoskeleton • Some cells have a network of protein filaments called the cytoskeleton which helps the cell maintain its shape and helps in all kinds of cell movement, including moving organelles around within the cell. • It is composed of microtubules and microfilaments.
Organelles in the Cytoplasm • Proteins are assembled on ribosomes. • The organelle where parts of the cell membrane are assembled and some proteins modified is called the endoplasmic reticulum. • rough ER – has ribosomes. Involved in the synthesis of proteins. • smooth ER - does not have ribosomes. Contains enzymes that perform specialized tasks.
Golgi • Proteins produced by ribosomes on the rough endoplasmic reticulum move into the Golgi apparatus, where carbohydrates and lipids are attached to proteins. • The Golgi apparatus is often called the “packaging” center of the cell.
Organelles • Lysosomes are the “trash men” of the cell and break down lipids, carbohydrates, and proteins from food into particles that can be used by the rest of the cell. Also break down dead organelles. • Cells store materials in saclike structures known as vacuoles. They also serve as support structures in plants, and transport structures in some animals.
Chloroplasts • Chloroplasts are found in plant cells. They use energy from sunlight to make energy-rich food particles in a process known as photosynthesis.
Mitochondria • Mitochondria are the powerhouse of the cell. They use energy from food to make high-energy compounds that the cell can use for growth, development, and movement.
Putting It Together • Unlike other organelles, chloroplasts and mitochondria contain some of their own genetic information in the form of DNA. • In humans, all of our mitochondria come from the cytoplasm of the egg cell. So thank your Mom for your mitochondria!
Comparing • There are 2 main things that plant cells have that animal cells do not: • The cell wall, which is made of rigid fibers • Chloroplasts which are used in the process of photosynthesis which makes food from sunlight.
Plant cells contain cell walls, large vacuoles, and chloroplasts (think photosynthesis) • Animal cells do not contain cell walls or chloroplasts
Comparing Cells • The biggest distinction between cells is between prokaryotes and eukaryotes: • Prokaryotes have a cell membrane but do not have a nucleus • Eukaryotic cells are larger and have a nucleus and more specialized organelles
The Cell as a Factory • The supporting structures that keep the factory standing are similar to the function of the cytoskeleton in the cell. • The factory boss is like the cell’s nucleus • The managers who take the orders to the work stations are like RNA in the cell • The work stations, where candy production happens, are like the cell’s ribosomes, which are located on the endoplasmic reticulum
The Cell as a Factory • The packaging part of the cell is the Golgi apparatus • The “power” to run the cell comes from the chloroplasts in plant cells. The “power” is used by the cell’s mitochondria for energy. • The “trash men” of the cell are the lysosomes.
