Chromosomes and DNA • Each chromosome contains a long strand of DNA • Body cells contain 23 pairs of chromosomes
Chromosomes and DNA • DNA carries the code that controls what cells are made of and what they do
The rungs of the DNA ladder are made from pairs of bases • There are four bases • These bases always pair together in the same way • How do you think the four bases pair up?
Aalways pairs withT Calwayspairs withG
DNA and Protein Synthesis • DNA contains the genetic information to • make amino acids • Amino acids combine to make proteins • These proteins determine the physical traits • of an organism and control cellular functions. • Proteins do everything, • and DNA gets all the • credit! • Think of them as tiny minions • who do all the work
DNA and Protein Synthesis • Codon: three bases code for a specific protein: • ex: AAA = Lysine • The codons code for 20 amino acids • Just like the alphabet has 26 letters to make all • the words we know, the 20 amino acids make • all the different proteins found in living • organisms • The codons are the template for protein synthesis, • which takes place on the ribosomes (rRNA) in the • cytoplasm
DNA and Protein Synthesis - Transcription • Transcription: • 1) DNA unzips • 2) mRNA (messenger ribonucleic acid) copies info from DNA using base pairings • RNA is different from DNA • Single stranded, not double stranded • Instead of deoxyribose, it has ribose • instead of Thymine, it uses Uracil • 3) Carries the genetic code from the nucleus to the • ribosome in the cytoplasm
The amino acids join together to form a protein • We need proteins to make and repair cells • Proteins are made in the cytoplasm
DNA and Protein Synthesis • Amino acids are linked together in the same • order as the codons , creating a protein chain • Just like linking letters to make words, linking • amino acids makes proteins mRNA CUAAUGUGC Amino Acid Amino Acid Amino Acid
DNA Mutations • What is a mutation? • Change in the DNA of a gene. 2) When a cell puts its genetic code into action it is making precisely the proteins it needs for its structure and function. 3) If something changes a gene’s code words, the resulting protein may change. 4) If the protein is central to the cell’s architecturethen a mutation could result in an abnormal cell.
DNA and Mutations • Mutations are any changes that take place in DNA: • Can be spontaneous or caused by mutagens • ex: Chemicals, high temperatures, UV light, • radiation • Can change the genetic code, and be replicated • when forming new body cells. • In sex cells, can be passed on to offspring. • Mutations can be neutral, beneficial, or harmful • ex: Blue eyes – a mutation that occurred 6-10,000 years ago, can be traced back to one ancestor • what kind of mutation is that?
Types of Gene Mutations 1) Substitution- can be a simple substitution in one base of the gene sequence. For example: Original: CAC GCC ATT GCG ATG Mutation: CAC GCC ATG GCG ATG One amino acid will replace another in this type of mutation thereby altering the resulting protein.
DNA and Mutations – Lets looks at different mutations THE DOG BIT THE CAT
DNA and Mutations - Substitution • THE DOG BIT THE CAT • Substitution - Replace just one letter: • THE DOG BIT THE CAR
Types of Gene Mutations 1) A Substitution is a Point Mutation Because it occurs at only one base in the DNA Strand.
Types of Gene Mutations Remember that DNA sequences are read in groups of three (codons) so we can use a simple sentence to demonstrate a substitution. Original – The Fat Cat Ate The Wee Rat Substitution – The Fat Hat Ate The Wee Rat Where did the substitution occur? The letter “C” in Cat was changed to an “H”
Gene Mutations – Substitutions: Sickle Cell Anemia Sickle Cell Anemia is a disease of red blood cells. Codon for glutamic acid has been changed to code for valine because of a substitution in one codon in the gene for the protein hemoglobin. Four hemoglobin proteins carry oxygen inside red blood cells. The change in the amino acid causes the hemoglobin to fold abnormally causing a sickle shaped red blood cell.
Sickle Cell Anemia The mutation affects the folding and stability of the hemoglobin protein
Frameshift Mutations-Insertions and Deletions Insertions and Deletions can be point mutations One or several base pairs are inserted into a gene or deleted from it. This results in a shift in the reading frame or “frameshift”. Therefore insertions and deletions are called “frameshift mutations”
DNA and Mutations - Deletion • THE DOG BIT THE CAT • Deletion: Delete just one letter (T): • THE DOG BIT HEC AT
DNA and Mutations-Insertions • THE DOG BIT THE CAT • Insertion - Add just one letter (E): • THE DOE GBI TTH ECA T • Cells have “proof reading” proteins that constantly check the DNA and fix errors, so most are corrected
Frameshift Mutations Frame- Shift Mutation in DNA can be demonstrated with a simple sentence. Original – The Fat Cat Ate The Wee Rat Frame Shift – The Fat CaAteTheWeeR at. Which letter (base) was deleted? The letter “t” in CAT.
Deletions Some times whole sections of genes are deleted. Original – The Fat Cat Ate The Wee Rat Deletion– The Fat Ate The Wee Rat Where did the deletion occur? The word “Cat” was deleted.
Insertions (Duplications and Tandem Repeats) Sometimes whole sections of genes are inserted. Original – The Fat Cat Ate The Wee Rat Insertion– The Fat Cat Cat Ate The Wee Rat a duplication or…. Original – The Fat Cat Ate The Wee Rat Insertion– The Fat Cat CatCat Ate The Wee Rat ….a tandem repeat (duplication continues through several generations)
How do Mutations Occur? • Can occur spontaneously when copying errors occur (replication is fast and there are lots of free nucleotides around during replication.) 2) Exposure to mutagens – mutation causing agents in the environment
Types of Mutagens Ultraviolet radiation in sunlight – Skin cancer may result!!!
Types of Mutagens 2) X-rays
Types of Mutagens 3) Environmental Agents Natural or manmade chemicals in the environment Many carcinogens or cancer-causing agents disrupt DNA.
How are mutations fixed? • Proofreading- cells have built in mechanisms that catch and repair most of the changes that occur in DNA. • Mutations in eukaryotic cells are rare. • In somatic cells any good or bad consequences will not be passed on to offspring. • If a mutation occurs in a gamete it may be passed to the next generation.
Mutation and Evolution A mutation and the protein made from the mutated gene that is passed from generation to generation (inherited) can have a beneficial, harmful, or neutral effect on an organism’s ability to survive in its prevailing environment. Therefore, gene mutations provide the foundation for change in a population of organisms – mutations provide the foundation for evolution by natural selection.
Mutation Practice Original DNA: TAC CTC GTA AAC CCT TAA GGG ACT Mutation 1: TAC CTC GTA CAC CCT TAA GGG ACT Circle all that apply: Deletion, Addition, Substitution, Inversion, Duplication