Chapter 4 Genetics: The Science of Heredity

Transcription

1 Chapter 4 Genetics: The Science of Heredity The Cell s Genetic Code Heredity is the passing of traits from parent to offspring Genetics is the scientific study of passing of traits from parent to offspring DNA is the chemical that makes up the genetic code Deoxyribonucleic acid Chromosome is a rod-shaped structure made of many genes linked together. Contains chromatin-dna wrapped in protein. Cell is the basic structure or unit of living things Nucleus is the control center of a living cell. Controls all cell activities Gene is a segment of DNA that codes for one trait or protein

2 The Code (pages , and ) Base Pairs Cytosine Guanine Thymine Adenine Genetic code is the order (sequence) of bases that stores information for directing the cell s activities (chemical reactions)

3 Base Pairs DNA A-T C-G RNA A-U C-G DNA segment AGT CGA TAC Codon RNA segment UCA GCU AUG Codon- three-base sequence that codes for one amino acid. Example: ACG. Amino acids form proteins.

4 How the Cell Uses the Genetic Code (pages 133 to 135) RNA is a chemical that copies and reads the genetic code. RNA stands for Ribonucleic Acid. RNA is found in the nucleus and cytoplasm of a cell. In what three ways is RNA different from DNA? RNA has one strand, DNA has two strands (double-helix) RNA has uracil base instead of thymine base. RNA has ribose sugar instead of deoxyribose What are the two kinds of RNA and what is the function of each? Messenger RNA that copies the genetic code Transfer RNA reads the code by bringing different amino acids to a ribosome Label the diagram below and then explain how the cell uses the genetic code. amino acids ribosome trna mrna The mrna brings the genetic code message to a ribosome. At the ribosome the trnas bring amino acids in the cytoplasm to the ribosome. The three-base sequence (codon) pairs up with the matching bases on the mrna. Each codon codes for one of the 20 different amino acids. The chain of amino acids forms a protein.

5 Protein Synthesis (pages 133 to135) Label and explain each step. Step 1 In the nucleus the DNA helix unzips. The information (message) is copied by the mrna. The mrna leaves the nucleus and enters the cytoplasm. Step 2 In the cytoplasm the mrna attaches to a ribosome. trnas made of three-base sequences (codons) begin to read the message by pairing up its codons with the mrna bases. Step 3 The trnas continue to bring amino acids to the ribosome. The trnas pair up with the bases on the mrna. An amino acid chain starts to form. Step 4 Eventually the enter message is read and the long chain of amino acids forms a protein.

6 Uses of Proteins Found in cell membranes as transport proteins Enzymes in cells that control chemical reactions (activities) Outer structures in animals such as feathers, horns, fingernails, hair, and fur Examples: o Hemoglobin o amylase o pepsin o fibrin o antibodies o marker molecules

7 Mutations A mutation is any change in a gene or a chromosome. Types of Mutations Substitution- one base pair is substituted for another Deletion- one base pair is removed Addition- one base pair is added Chromosome not separating properly during cell division Effects of Mutations Can be a source of genetic variety May be harmful if it reduces an organism s chance of survival and reproduction. Ex. White lemur in the wild is easy for predators to spot. Helpful if it improves chances of survival. Ex. Antibiotic resistance in bacteria. No effect