Biology Chapter on Genes and Proteins

Genes

• Most characteristics (e.g., hair color, height) depend on the proteins your cells produce.
• DNA stores the instructions for making proteins.
• The instructions for a specific protein are found within a gene.
• A gene is a section of DNA located on a chromosome.

Genes on a Chromosome

• Chromosomes are depicted as an X shape or a long strand.
• DNA is a long strand that contains genes.
• Genes are arranged along the DNA strand in a specific order. A single gene is a short section of the chromosome.
• A chromosome is made of two chromatids joined by a centromere.
• A human cell nucleus has 23 pairs of chromosomes. (e.g., two copies of #19, two copies of #12).

Proteins

• Proteins are chains of hundreds or thousands of amino acids.
• The order of amino acids is determined by the gene. A gene determines the order of amino acids.
• Proteins build cells and tissues, or act as enzymes.

Making Proteins

• Proteins are made on ribosomes within the cytoplasm.
• Ribosomes receive instructions from RNA.
• RNA carries the code from the nucleus to the ribosome (transcription).
• The RNA message is then translated into a specific protein (translation) at the ribosome.

RNA

• RNA is made in the nucleus based on the DNA pattern.
• RNA is different from DNA in structure. It's a single-stranded molecule.
• RNA is like a ladder with its rungs cut in half, meaning it's single-stranded.
• RNA includes the bases A, G, C, and U (uracil), excluding thymine.

DNA to RNA

• DNA in the nucleus is used to create RNA.
• RNA carries the protein code from the nucleus to the ribosome (transcription).
• At the ribosome, the RNA message is translated into a specific protein (translation).

Controlling Genes

• Cells have the same chromosomes and genes.
• Cells do not always produce the same proteins due to different genes being expressed.
• Each cell utilizes a subset of genes to create proteins specific to its function.

How Cells Control Gene Expression

• Sometimes DNA is tightly wound preventing RNA production (transcription).
• Sometimes chemicals bind to DNA preventing its use.
• Incorrect proteins affect the organism's function.
• RNA is made in the nucleus, then carries the genetic code to the ribosomes to produce proteins.

Mutations

• Mistakes can occur during DNA replication.
• Mistakes in DNA replication may lead to incorrect proteins.
• Mutations are permanent DNA sequence changes in a gene or chromosome of a cell. These changes can affect protein structure and function.

Mutation Factors

• Outside factors like X-rays, sunlight, and chemicals can cause mutations.
• Mutations can be positive or negative.
• Negative mutations can result in cells with extra chromosomes or missing chromosomes, leading to various health problems.
• Positive mutations introduce variety to species or allow plants to create chemical insect repellents.