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Science 10 Unit 1 GENETICS 1.1 DNA Structure and Function Part I- The Nucleus: Control Centre of the Cell • Every cell in your body has a specific JOB- but how do they become specialized? E.g. hair cells vs. skin cells vs. retina in the eye The NUCLEUS in the cell contains the master set of instructions that tells the cell: • what it will BECOME • how it will function • when it will REPRODUCE and GROW • when it will die 1.1 DNA Structure and Function • But how does the nucleus do this? How does it send messages to the rest of the cell? 1.1 DNA Structure and Function The nucleus contains DNA, which carries the master set of INSTRUCTIONS for cell function. • DNA (DEOXYRIBONUCLEIC ACID) is a double stranded helix that looks like a twisted ladder • the sides of DNA are made of SUGAR and PHOSPHATES • the steps of DNA are made up of 4 BASES: Adenine Cytosine Guanine Thymine 1.1 DNA Structure and Function • Where are the bases located? • Name the 4 bases • Where are the sugars and phosphates located? • What is this shape called? 1.1 DNA Structure and Function Pairing Rules • adenine (A) always pairs with THYMINE (T) Apple Tree • cytosine (C) always pairs with GUANINE (G) Car Garage 1.1 DNA Structure and Function 2. DNA has many functions: A. DNA contains INSTRUCTIONS FOR ALL CELL FUNCTIONS and, therefore, DNA indirectly controls all of the functioning of all living things. B. DNA DETEMINES THE HEREDITARY TRAITS of an individual C. DNA EVOLVES (changes through mutations and recombination). This allows for new characteristics & abilities to appear which may help an individual to survive & reproduce. D. Self replication: DNA has the ability to MAKE COPIES OF ITSELF. 1.1 DNA Structure and Function 3. The arrangement of bases in DNA directs all cell activity • the bases are like letters that carry a message (CODE) • the code gives INSTRUCTIONS for a specific task. 1.1 DNA Structure and Function 4. DNA is stored in the form of chromatin • chromatin is made up of DNA and PROTIENS called histones (very dense) • when a cell is growing, parts of the CHROMATIN unwind so that the targeted section of DNA can be read to make messages that control the rest of the cell. • when cells reproduce, the entire chromatin coils up and makes an X-shaped structure called a CHROMOSOME Some terms you should know…. 1.1 DNA Structure and Function 5. Every organism has a characteristic number of chromosomes • chromosomes are always in PAIRS in the nucleus • humans have 46 chromosomes (=23 pairs) • in males, the 23rd pair of chromosomes are “XY” • in females, the 23rd pair of chromosomes are “XX” • cows have 60 chromosomes; corn has 20 chromosomes 1.1 DNA Structure and Function 6. Genes are found on chromosomes • A GENE is a small segments of DNA found at specific places on a chromosome that code for a protein • genes can vary in length from 100s to 1000s of BASES • the arrangement of bases will decide what kind of protein is produced e.g. ACCATAGG make protein “A” AGGCGTTA make protein “B” 1.1 DNA Structure and Function • each chromosome carries 1000s of GENES • your body uses 90 000 to 100 000 different PROTEINS 1.2 Protein Synthesis Part I- The Role of Proteins Why are proteins so important anyways? • Humans share most of the same protein families with WORMS, flies, and plants • Hair grows by forming new cells at the base of the root. As they move upward through the skin they are cut off from their nutrient supply and start to form a hard protein called KERATIN. As this occurs, the hair cells die. The dead cells and keratin form the shaft of the hair. 1.2 Protein Synthesis • Fingernails grow about THREE TO FOUR times as quickly as toenails • Each hair grows about 1/4 INCH/month and grows for up to 6 years. • The most expressive muscles are the facial muscles. We need 17 muscles to smile and 43 muscles to frown. • The most numerous are the skeletal muscles. When we walk for instance, we use 200 muscles. 1.2 Protein Synthesis Proteins Have 2 Main Functions 1. Structural: proteins help make up all structures in living things Examples: a) MUSCLE PROTEINS b) HAIR, NAILS, BONES c) BLOOD VESSELS, LIGAMENTS 1.2 Protein Synthesis 2. Functional: other proteins help us to keep our bodies functioning properly and to digest our food. Examples: a) ENZYMES TO SPEED UP CHEMICAL REACTIONS b) HAEOMOGLOBIN IN RED BLOOD CELLS c) ANTIBODIES USED IN THE IMMUNE SYSTEM d) TRANSPORT PROTEINS FOUND IN CELL MEMBRANES 1.2 Protein Synthesis • Only certain genes are ACTIVATED in a cell • Depending which genes are active, different proteins are produced, and this causes cells to have different functions. E.x. You do not have skin pigment genes being used by your stomach cells • ONE GENE ONE TYPE OF PROTEIN ONE FUNCTION 1.2 Protein Synthesis Part II- Protein Synthesis • The making of proteins can be broken down into two steps: 1. TRANSCRIPTION 2. TRANSLATION 1.2 Protein Synthesis Act One: TRANSCRIPTION (Trans = across, cription = to write) • The coded message of a gene on DNA has INSTRUCTIONS on how to make particular PROTEINS that our bodies need. • The instructions from a gene are copied from DNA to MESSANGER RIBONUCLEIC ACID (MRNA) in the nucleus. 1.2 Protein Synthesis • RNA has slightly different bases: A, G, C and URACIL instead of thymine • Once complete, the mRNA moves through the NUCLEAR PORES and into the cytoplasm where the proteins are made. • The process of making mRNA is called TRANSCRIPTION 1.2 Protein Synthesis Watch the General Process • Step 1: UNZIPPING of the DNA from a double strand into two single strands • Step 2: RIBOSOMAL BASES pair up with the bases on one of the DNA strands to form mRNA • Step 3: ENZYMES help form the RNA BACK BONE and checks for ERRORS • Step 4: The MRNA is released, leaves the nucleus, & the DNA ZIPS BACK UP 1.2 Protein Synthesis Messenger RNA 1.2 Protein Synthesis Act Two: TRANSLATION • The mRNA moves into the cytoplasm and pairs up with a RIBOSOME. It is here that the mRNA will be “read” to make a protein. • The mRNA code is made up of groups of TRIPLET_CODES known as CODONS. Each codon codes for a specific AMINO ACID. Eg. AGC = Serine Eg. UGC = Cysteine 1.2 Protein Synthesis • It takes 3_ bases to make one codon. Why? Because there are about 20 amino acids and we only have 3 BASES in the alphabet. – With a _SINGLE_ nucleotide, there are only 4 possible codes (41). – For _DOUBLE_ nucleotides, there are only 16 possible codes (42). – However, for _TRIPLET_ nucleotides there are 64 possible codes (43) 1.2 Protein Synthesis • The amino acid for each codon is given in the tables below: • Now you try. What is the amino acid for each of the following codons? CAU : _____________ AUG : _______________ CAU : ____________ UGA : ___________ GCC : ________________ AAA : ____________ 1.2 Protein Synthesis • During translation, the written code (codons) on mRNA is ‘TRANSLATED’ into a specific amino acid sequence by TRANSFER RIBONUCLUEIC ACID (tRNA) in the cytoplasm. • A tRNA molecule is a small piece of RNA that has an AMINO ACID attached to it. • The tRNA also has a special sequence of 3 bases known as an ANTICODON. • There is at least one type of tRNA for each of the 20 amino acids. 1.2 Protein Synthesis • As the correct AMINO ACIDS are brought to the ribosome by the tRNAs, they are joined together to form the PROTEIN CHAIN that the original DNA coded for. • Eventually, the finished protein chain moves to the GOLGI BODY, where it is packaged and released to do its “job”. SUMMARY OF PROTEIN SYNTHESIS: Describe what happens at each step: 1. _______________________________ _________________________________ _________________________________ 2. _______________________________ _________________________________ _________________________________ 3. _______________________________ _________________________________ _________________________________ 4. _______________________________ _________________________________ _________________________________ 5. _______________________________ _________________________________ _________________________________ 6. _______________________________ _________________________________ _________________________________ 7. _______________________________ _________________________________ _________________________________ 8. _______________________________ _________________________________ _________________________________ 9. _______________________________ _________________________________ _________________________________ Worksheet: DNA AND PROTEIN SYNTHESIS REVIEW 2.1 Mutations A BAD NIGHT AT THE THEATRE Question: What if something goes wrong during translation? Answer: IF TRANSLATION IS ALTERED, THE PROTIEN PRODUCT WILL BE DIFFERENT • Mutations can CHANGE in the base sequence of DNA • When the BASES (‘letters’) change, the INSTRUCTIONS used to make the protein also change. • Different AMINO ACIDS will be used, resulting in a different protein. This may alter protein shape, and also change or “break” protein function. 2.1 Mutations There are 2 types of MUTATION: 1. CHROMOSOMAL mutations: a mutation of all or part of a chromosome. • This usually involves LARGE SEGMENTS OF DNA, and therefore, CAN HAVE GREATER IMPACT THAN SMALLER GENE MUTATIONS . • There are four types of chromosomal mutations that involve part of the chromosome: Chromosomal Mutations… 2.1 Mutations • E.g. Fruit fly with legs in place of antennae. This mutation involves moving a controller gene telling the fruit fly where to put the legs • E.g. Down’s syndrome. This is a genetic disorder where there is an extra chromosome #21. The extra chromosome resulted from improper cell division. • Examples: Down’s syndrome – (Trisomy 21) 47 chromosomes, extra chromosome at pair #21 2.1 Mutations 2. GENE mutations: a mutation that occurs within a gene at some point along a chromosome. This mutation is only a change of one or a few ‘letters’ (bases). • It usually only affects ONE GENE, and therefore, CAN HAVE LESS IMPACT THAN LARGER CHROMOSOMAL MUTATIONS. 2.1 Mutations • Recall the sequence of protein synthesis: DNA RNA ACTGCT…. UGACGA…. (in nucleus) (to cytoplasm) protein leu- ade-cyt… (at ribosome) • If the sequence of DNA changes by mutation, then the RNA sequence copied from the DNA will be different, and this will code for a different amino acid, which results in a different protein. This is called a GENE MUTATION • E.g. the Land of the Spirit Bear is _WHITE_ because the gene that codes for _FUR_COLOUR_ (dark brown) is mutated and no longer works 2.1 Mutations • there are three main ways that gene mutations can occur: Substitution e.g. replace “C” with “A” ACTGCA AATGCA Deletion e.g. lose a base all together ACTGCA ACGCA Addition e.g. add another “A” ACTGCA ACTAGCA 2.1 Mutations I. Types of Gene Mutations • mutations are often a bad thing because the protein does not work and your body needs it to function. These are known as NEGATIVE MUTATIONS and they DECREASE_ survival rates. • e.g. mutated gene SICKLE-CELL ANEMIA (misshapen red blood cells that don’t carry O2). • e.g. more than 1300 different mutations in one gene CYSTIC FIBROSIS (build up of mucus in the lungs) Sickle Cell Anemia and Cystic Fibrosis 2.1 Mutations • sometimes mutations can be a good thing (e.g. the mutated protein works better than the “normal” protein or has a new beneficial function). These are known as POSITIVE MUTATIONS and they INCREASE survival rate. • e.g. mutated gene proteins that make them RESISTANT TO HIV INFECTION. These people cannot get AIDS. • e.g. some plants have mutated genes that codes for proteins that make them RESISTANT TO CHEMICAL HERBICIDES. 2.1 Mutations • sometimes mutations have no effect because they occur in a part of the DNA that is not used for protein synthesis or the mutated protein is not required for survival. These are known as NEUTRAL MUTATIONS and have they have NO EFFECT on the organism. • e.g. mutation in the gene that codes for fur colour (Spirit Bear). Although white, the survival rate of the organism is not changed. 2.1 Mutations II. Causes of Mutations • Mutations can occur naturally during DNA replication and cell division. The human body has systems in place that will often fix errors in DNA replication, or destroy cells that are working abnormally due to mutations. • There are also factors in the environment that may increase chances for mutations to occur. 2.1 Mutations • MUTAGENS= substances or factors (e.g. virus, cigarette smoke, Xrays) that can cause mutations in DNA 2.2. Uses of Biotechnology I. Gene Therapy • Researchers are testing new techniques called GENE THERAPY to treat mutated genes. This is still a risky, new area and is not yet a perfect solution to gene mutations. Gene Therapy What are the potential gains for gene therapy? What are the potential risks? What are the prospects for gene therapy in the future? 2.2. Uses of Biotechnology 2.2. Uses of Biotechnology II. Genetic Engineering and Genetically Modified Organisms 1. What is genetic engineering? • Genetic engineering is altering the genetic makeup of an organism by CUTTING DNA from one organism and INSERTING FRAGMENTS into a host. • The end result is RECOMBINANT DNA, or DNA made from two or more different organisms. 2.2. Uses of Biotechnology • Genetic engineering changes the ALLELE FREQUENCY of a population by ARTIFICIAL MEANS • E.x. Scientists have made a glow in the dark plant. They did this by removing the fire fly gene from a firefly and inserting it into the plant cell using cut and paste enzymes. • An organism that has DNA from another organism is called TRANSGENIC (“trans” means across, “gene” means race) Public Opinion of GMO’s Your turn to do some research: • • • • • What does the general public think of GMO’s? What science do they have to back their claims? Are there any untrue or invalid claims about GMO’s? What are the possible dangers of GMO’s? What are the possible benefits of GMO’s? 2.2. Uses of Biotechnology 2. The Process of Genetic Engineering The steps: • a. The desired DNA segment must be ISOLATED. This is done by CUTTING it out of the DNA strand • RESTRICTIVE ENZYMES are used to cut the DNA at very specific sites • Like “scissors”, leave behind “jagged” STICKY ENDS of DNA. 2.2. Uses of Biotechnology • b. Next, the DNA segment is put into a vehicle (VECTOR) that will transmit the DNA to the host cell • A vector can be a BACTERIUM or VIRUS, a pipette or a metal bullet covered with DNA • The vectors do the “dirty work” in that they insert the DNA into the host genome 2.2. Uses of Biotechnology • C. The DNA is then transferred to the host= TRANSGENIC ORGANISMS 2.2. Uses of Biotechnology 3. What are the uses for genetic engineering? • Grow human hormones in bacteria cultures • Artificial sweeteners using bacteria to make amino acids • Study human diseases by inserting human DNA into mice • Replace incorrect DNA sequences • Replace harmful bacteria on plants • Nitrogen bacteria in the soil & plants to make fertilizer • Improve transport of fruits • Resist diseases • Increase protein production 3.1 Genetics • Who is Gregor Mendel? ” Father of Genetics” • Principle of Independent Assortment - Inheritance of one trait has no effect on the inheritance of another trait. 3.1 Genetics Traits • Genetics – study of how traits are passed from parent to offspring. • Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait. 3.1 Genetics • Chromosomes come in homologous pairs, thus genes come in pairs. • Homologous pairs –matching genes – one from female parent and one from male parent • Example: Humans have 46 chromosomes or One set from dad – 23 in sperm . One set from mom – 23 in egg . pairs. 3.1 Genetics • One pair of Homologous Chromosomes: Gene for eye color (blue eyes) Homologous pair of chromosomes Gene for eye color (brown eyes) Alleles – different genes (possibilities) for the same trait – ex: blue eyes or brown eyes 3.1 Genetics Dominant and Recessive Genes • Gene that prevents the other gene from “showing” – dominant • Gene that does NOT “show” even though it is present – recessive. • Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t 3.1 Genetics Example: Straight thumb is dominant to hitchhiker thumb • T = straight thumb t = hitchhikers thumb • (Always use the same letter for the same alleles—No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt 3.1 Genetics • Both genes of a pair are the same – homozygous or purebred TT – homozygous dominant tt – homozygous recessive • One dominant and one recessive gene – heterozygous or hybrid Tt – heterozygous BB – Black Bb – Black with white gene bb – White 3.1 Genetics Genotype and Phenotype • Combination of genes an organism has (actual GENETIC makeup) – genotype Ex: TT, Tt, tt • Physical appearance resulting from gene make-up – phenotype • Ex: hitchhiker’s thumb or straight thumb 3.1 Genetics Punnett Square and Probability • Used to predict the possible gene makeup of offspring – Punnett Square 3.1 Genetics • Example: Black fur (B) is dominant to white fur (b) in mice • Cross a heterozygous male with a homozygous recessive female. Black fur Heterozygous male White fur Male = Bb X Female = bb White fur Homozygous recessive female White fur 3.1 Genetics Female Gametes - N ( One gene in egg ) Possible offspring – 2N Male gametes - N (One gene in sperm) 3.1 Genetics Write the ratios in the following orders: • Genotypic ratio 2:2 • 50% Bb : 50% bb homozygous : dominant heterozygous : • Phenotypic ratio 2:2 • 50% black : 50% white dominant : recessive b b B Bb Bb b bb bb homozygous recessive 3.1 Genetics • Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. Bb X Bb B b Genotypic ratio = 1 BB : 2 Bb : 1 bb B BB Bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = b Bb bb 3 black : 1 white 75% black : 25% white 3.1 Genetics • Example: A man and woman, both with brown eyes (B) marry and have a blue eyed (b) child. What are the genotypes of the man, woman and child? Man Woman 3.1 Genetics Sex Determination • People – 46 chromosomes or 23 pairs • 22 pairs are homologous (look alike) – called autosomes – determine body traits • 1 pair is the sex chromosomes – determines sex (male or female) 3.1 Genetics • Females – sex chromosomes are homologous (look alike) – label XX • Males – sex chromosomes are different – label XY 3.1 Genetics • What is the probability of a couple having a boy? Or a girl? • Chance of having female baby? A male baby? • Who determines the sex of the child? 3.1 Genetics Incomplete dominance and Codominance • When one allele is NOT completely dominant over another (they blend ) – incomplete dominance • Example: In carnations the color red (R) is incompletely dominant over white (W). The hybrid color is pink. Give the genotypic and phenotypic ratio from a cross between 2 pink flowers. ______ X ______ Genotypic = 1 RR : 2 RW : 1 WW Phenotypic = 1 red : 2 pink : 1 white 3.1 Genetics • When BOTH alleles are expressed –CODOMINANCE • Example: In certain chickens black feathers are codominant with white feathers. • Heterozygous chickens have black and white speckled feathers. ______ X ______ Genotypic = Phenotypic = 3.1 Genetics Sex – linked Traits • Genes for these traits are located ONLY on the X chromosome (NOT on the Y chromosome) • X linked alleles always show up in MALES whether dominant or recessive because males have only one X chromosome 3.1 Genetics Examples of recessive sex-linked disorders: • 1. Colorblindness – inability to distinguish between certain colors • Colour blindness is the inability to distinguish the differences between certain colours. The most common type is red-green colour blindness, where red and green are seen as the same colour. 3.1 Genetics • 2. hemophilia – blood won’t clot 3.1 Genetics • Example: A female that has normal vision but is a carrier for colorblindness marries a male with normal vision. Give the expected phenotypes of their children. N= normal vision n= colour blind Phenotype: 3.1 Genetics Pedigrees • Graphic representation of how a trait is passed from parents to offspring 3.1 Genetics Tips for making a pedigree • Circles are for females • Squares are for males • Horizontal lines connecting a male and a female represent a marriage • Vertical line and brackets connect parent to offspring • A shaded circle or square indicates a person has the trait • A circle or square NOT shaded represents an individual who does NOT have the trait • Partial shade indicates a carrier – someone who is heterozygous for the trait 3.1 Genetics • Example: Make a pedigree chart for the following couple. Dana is color blind; her husband Jeff is not. They have two boys and two girls. HINT: Colorblindness is a recessive sex-linked trait. Has trait Can pass trait to offspring 3.1 Genetics Multiple Alleles - 3 or more alleles of the same gene that code for a single trait • In humans, blood type is determined by 3 alleles– A, B, and O • BUT each human can only inherit TWO alleles 3.1 Genetics 1. Dominant – A and B (codominance) Recessive – O 2. Blood type – A = AA or AO B = BB or BO AB = AB O = OO 3.1 Genetics Example: What would be the possible blood types of children born to a female with type AB blood and a male with type O blood? __________ X__________ Children would be type ____ or ___ only