Cells, DNA, and You

Basic Cell Structures Cells come in many shapes and sizes. Despite differences in cell size and shape, certain structures are common to most cells. Cell membrane– the thin, flexible barrier around the cell. Cell wall- found only in plant cells, it is a strong layer around the cell membrane.

Some cells have a nucleus which is a large structure that contains the cell’s genetic material and controls the cell’s activities. The jelly-like material inside the cell membrane– but not including the nucleus– is called the cytoplasm. The cytoplasm contains many important structures.

Biologists divide cells into 2 categories: eukaryotes and prokaryotes. Eukaryotic cells have a nucleus. They also contain specialized structures called organelles. Prokaryotic cells do not have a nucleus. They are simple being composed of only a cell membrane and cytoplasm.

Prokaryotic v. Eukaryotic

All plant, animal, and fungi are eukaryotes, as well as many microorganisms. All bacteria are prokaryotes. Even though they are relatively simple, prokaryotes carry out every activity associated with life. They grow, reproduce, and respond to changes in the environment.

Nucleus The nucleus is the large structure which controls most cell processes and contains the hereditary information of DNA. DNA holds the coded instructions for making proteins and other important molecules. The nucleus directs the making of proteins, one of the main functions of cells.

Nucleolus– small, dense region within the nucleus where ribosome assembly begins. Ribosomes aid in the production of proteins within the cell. One of the most important jobs carried out in the cell is making proteins. Ribosomes– small particles made of RNA and proteins on which proteins are assembled. Nuclear envelope– double membrane that surrounds the nucleus. The envelope has pores which allows materials to pass in and out of the nucleus.

The granular material visible within the nucleus is called chromatin. Chromatin consists of fine strands of DNA bound to protein. When a cell divides, chromatin condenses to form chromosomes, which are rod-shaped structures that contain the genetic information to be passed on.

Nucleic Acids Nucleic acids are macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus. Nucleic acids are polymers assembled from individual monomers known as nucleotides. The nucleotide is made of 3 parts: a sugar group, a phosphate group, and a nitrogenous base.

Individual nucleotides join together to form a nucleic acid. Nucleic acids store and transmit genetic information. There are 2 kinds of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

DNA DNA is what enables cells to have so many different forms and perform so many different functions. In simple terms, DNA controls the production of proteins within the cell. These proteins in turn form the structural units of cells and control all chemical processes within the cell.

Every new cell that develops in your body needs an exact copy of the DNA from the parent cell. Additionally, humans and all other organisms must be able to pass copies of their DNA on to their offspring in order to continue the species. The structure of the DNA molecule is related to its 2 primary functions– to store and use information to direct the activities of the cell and to copy itself exactly for new cells that are created.

The DNA molecule consists of 2 long strands, each of which is a chain of nucleotide monomers. Each nucleotide has 3 parts: 1. a 5 carbon sugar molecule called deoxyribose 2. a phosphate group 3. a nitrogenous base While the sugar molecule and phosphate group are the same in every nucleotide, the nitrogenous base may be any one of four different kinds.

The 4 types of nitrogenous bases in DNA are adenine, guanine, thymine, and cytosine. Study the structure of each base in the picture on the following slide. Adenine and guanine belong to a class of organic molecules called purines which have a double ring of carbon and nitrogen atoms. Thymine and cytosine are pyrimidines and have a single ring of carbon and nitrogen atoms.

Each nucleotide– deoxyribose, phosphate, and nitrogenous base– bonds to other nucleotides to form a long strand. Two of these strands bonded together form a molecule of DNA. The 2 strands twist around a central axis to form a spiral structure called a double helix. The double helix was first described in 1953 by James Watson and Francis Crick. Their discovery was one of the most significant of the 20 th century.

The DNA molecule looks something like a twisted ladder. The sides of the ladder are formed by alternating sugar and phosphate units, and the rungs consist of bonded pairs of nitrogen bases. The rungs of the DNA ladder are always of uniform length because in each case one base is a double-ringed purine and the other is a single-ringed pyrimidine

The two strands of DNA are held together by hydrogen bonds between the bases. A hydrogen bond is a type of weak chemical bond that occurs between hydrogen atoms and more electronegative atoms like oxygen, nitrogen, and fluorine.

Cell Cultures Scientists may take a single cell or a few cells from the same tissue and place them into a dish containing a nutrient solution. The cell is able to reproduce so that a group of cells, called a cell culture, develops from the original cell or cells. Cell culture typically refers to the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment.

The cells may be removed from the tissue directly and then separated using enzymes or mechanical means. The cells may also be derived from a cell line or cell strain that has already been established.