Cell Structure and Function

Life is Cellular Since the 1600s, scientists have made many discoveries about the cells of living things. Cell Theory: – All living things are made up of cells. – Cells are the basic units of structure and function in living oranisms. – New cells are produced from existing cells.

Characteristics of Cells All Cells share 2 characteristics: 1- A barrier called a cell membrane that surrounds the cell. 2- All cells at some point in their lives contain DNA. DNA is the molecule that carries biological information.

Types of Cells Cells fall into 2 broad groups based on whether they have a nucleus. 1- Prokaryotes 2- Eukaryotes Nucleus- is a membrane enclosed structure that holds the cell’s genetic material (DNA). Nucleus controls many of the cells’ activities.

Cell Types cont’d Prokaryotes: - Do not have nuclei. -Their genetic material is NOT contained in a nucleus. -Bacteria are prokaryotes. Eukaryotes: -Are cells that have nuclei. -Have a nucleus which separates their genetic material from the rest of the cell. -Plants, animals, fungi, and protists are eukaryotes

Eukaryotic Cell Structure Eukaryotic cells are divided into 2 main parts: 1- The nucleus 2- The cytoplasm Cytoplasm- is the part of the cell outside the nucleus.

Nucleus… -Contains most of a cell’s DNA. -Is surrounded by a double membrane called a nuclear envelope. -Has a small dense region known as the nucleolus.

Vocabulary DNA- contains the coded instructions for making proteins and other important molecules. Chromatin- is made up of DNA attached to proteins. When the cell divides, this chromatin condenses into chromosomes. Chromosomes- are threadlike structures. They contain the genetic information that is passed from one generation of cells to the next. Nucleolus- in the nucleus, it’s where ribosome begins to be made.

In the Cytoplasm… Eukaryotic cells have structures called organelles inside the cytoplasm.

Organelles… Ribosomes: are small particles of RNA and protein spread throughout the cytoplasm. Endoplasmic Reticulum (ER): is an internal membrane system. This is where lipid compounds of the cell membrane are assembled, along with proteins and other material the are exported from the cell.

ER Cont’d Rough ER: Is involved in protein synthesis. Smooth ER: helps make lipids.

Organelles cont’d Golgi apparatus: look like closely grouped membranes. - it changes, sorts, and packages proteins and other material from the ER for storage in the cell or secretion outside the cell. Lysosomes: are small organelles filled with enzymes. - Help break down lipids, carbohydrates and proteins into small molecules that can be used by the rest of the cell.

Organelles cont’d Vacuoles: are small sac like structures that are used to store materials. Mitochondria: convert the chemical energy stored in food into compounds that are more convenient for the cell to use. Chloroplast: capture the energy in sunlight and convert it into chemical energy. Cytoskeleton: a network of protein filaments that helps the cell maintain its shape. - Involved in movement.

Cytoskeleton Cont’d Microfilaments- are threadlike proteins that form a network in some cells and produce a tough flexible framework that supports the cell.

Cell Boundaries Cell membrane: 1- Controls what enters and leaves the cell. 2- Protects and supports the cell.

Cell Wall Plants, algae, fungi, and many prokaryotes have a strong supporting layer called a cell wall. The main job of the cell wall is to support and protect the cell.

Functions of the cell wall One of the most important functions of the cell membrane is to control the movement of dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

Movement outside the cell Cilia- are short hair like projections that help the cell in movement. Flagella- are tail like projections that help the cell in movement.

Movement inside the cell The solution inside the cytoplasm is a combination of many substances in water.

Diffusion Diffusion is the process of particles moving around from an area where they are more concentrated to an area where they are less concentrated. Does not require energy.

Osmosis Is the diffusion of water through a “selectively” permeable membrane.

Selectively permeable membrane Is a membrane that some substances CANpass through, while others CANNOT. So how do other substances pass through the cell membrane? - Protein channels

Protein channels Allow certain molecules to cross the membrane. Help/ facilitate the diffusion of the molecules across the membrane. This process is called facilitated diffusion.

Facililtated diffusion Does not require the cell to use energy.

Active Transport Requires energy. Happens when cells move materials from one side of the membrane to the other side against the concentration difference. There are 4 types: – Endocytosis – Phagocytosis – Pinocytosis – exocytosis

Active Transport cont’d Endocytosis- the process of taking material into the cell by infolding of the cell membrane Phagocytosis- the extension of cytoplasm to surround a particle and package it within a food vacuole. Pinocytosis- The taking up of liquids from the environment. Exocytosis- The release of materials from the cell.