Biology Study Guide Midterm Trimester Three

Transcription

1 Biology Study Guide Midterm Trimester Three Chromosome number o Homologous chromosomes are pairs of chromosomes that correspond in body cells One chromosome pair comes from each parent o Diploid means that two sets and a cell that contains both sets of homologous chromosomes The number of chromosomes is represented by 2n Diploid cells contain two complete sets of chromosomes and two complete sets of genes Means two sets o Haploids contain only a single set of chromosomes and genes Means one set Gametes are haploid Meiosis o During meiosis the number of chromosomes per cell is cut in half through the separation of the homologous chromosomes The process that somatic/diploid cells undergo when a single cell divided to make four unique haploid daughter cells It only occurs in sexually reproducing animals because in sexual reproduction the chromosomes of one parent are combined with that of the other parent to produce a genetically unique offspring o Interphase I: cells undergo a round of DNA replication forming duplicate chromosomes o Meiosis I: Prophase I: each replicated chromosome pairs up with its corresponding homologous chromosome forming a tetrad during tetrad formation alleles can be exchanged between chromatids a process called crossing over Tetrads have a close association of sister chromatids of homologous chromosomes (4) Crossing over is when homologous chromosomes exchange small pieces resulting in new combinations Metaphase I: paired homologous chromosomes line up in the center of the ell Anaphase I: the fibers pull the homologous chromosomes toward the opposite ends of the cell Independent assortment occurs making new combinations, chromosomes from the mom and dad randomly move to one side to the other Telophase I: a nuclear membrane forms around each cluster of chromosomes cytokinesis then occurs resulting in two new cells the resulting daughter cells contain chromosome sets that are different from each other and from the parent cell o Meiosis II: 1

2 Prophase II: meiosis I results in two haploid (n) daughter cells each with half the number of chromosomes as the original cell Metaphase II: the chromosomes line up in similar way to the metaphase stage of mitosis Anaphase II: the sister chromatids separate and move towards the opposite sides of the cell Telophase II: meiosis II results in 4 haploid (n) daughter cells During fertilization two gamete unite forming a zygote o Phases of meiosis: Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell Has two main stages: The first meiotic division is meiosis I The second meiotic division is meiosis II By the end of meiosis II the diploid cells that entered meiosis has become four daughter haploid daughter cells o Meiosis I: Before meiosis I each chromosome is replicated The cell than begins to divide in a way similar to mitosis In mitosis four chromosomes line up individually in the center of the cell, the two chromosomes that make up each chromosome then separate from each other As chromosomes pair up and form tetrads, they may exchange their chromatids in a process called crossing over Crossing over results in the exchange of alleles between homologous chromosomes and produces new combinations of alleles Next homologous chromosomes separate and two new cells are formed although the cell now has four chromosomes like mitosis it is different because each pair of homologous chromosomes are separated neither of the daughter cells have two complete sets of chromosomes like in a diploid cell Those two sets have been shuffled like a deck of cards The two cells produced by meiosis I have sets of chromosomes and alleles that are different from each other and from the diploid cells that entered meiosis I o Meiosis II: The two cells from meiosis I now enter a second meiotic division, unlike the first division neither of the cells goes through a round of chromosome replication before entering into meiosis II Each of the cells chromosomes has two chromatids During metaphase II of meiosis II chromosomes line up in the center of the cell In anaphase II the paired chromatids separate each of the four daughter cells now contain the haploid number (n) just two chromosomes each 2

3 o Gamete formation In male animals haploid gametes produced by meiosis are called sperm In some plants pollen grains contain haploid sperm cells In female animals generally only one of the cells produces by meiosis is involved in reproduction The female gamete is called an egg cell and is also in some plants In many female animals the cells divisions at the end of meiosis I and II are uneven so the egg or egg cell revives most of the cytoplasm The other three cells produces in the female during meiosis are known as polar bodies and usually don t participate in reproduction o Comparing meiosis and mitosis Mitosis results in the production of two genetically identical diploid cells whereas meiosis produces four genetically different haploid cells A diploid cell that divides by mitosis gives side to two diploid (2n) daughter cell the daughter cells have sets of chromosomes and alleles that are identical to each other and to the original parent cell One division Meiosis begins within a diploid cell but produces four haploid (n) cells These cells are genetically different from the diploid cell and one another Two divisions Makes new combinations using crossing over and independent assortment o Quick notes Another term for body cells is somatic or diploid cells (same name/thing, 2n) There are two types of gametes: sperm and eggs (n) they are haploid Somatic cells are diploid, some examples are nerve, brain, muscle, and skin cells If a cell has 26 chromosomes in a liver cell they will have 26 chromosomes in somatic/diploid cell (2n) and 13 in a haploid/sex cell (n) Gametes have an odd number of chromosomes While a haploid number may be even of odd, the diploid number is always even The offspring of two parents obtains a single copy of every gene from each parent A gamete must contain one complete set of genes A pair of corresponding chromosomes is homologous One member of each homologous chromosome pair comes from each parent A cell that contains both sets of homologues chromosomes is diploid Meiosis makes sex cells o Chromosomes and meiosis vocab Genes: DNA passed from parent to offspring that determines your traits Gametes: sex cells; sperm of eggs, always haploid Haploid: half the amount of DNA (abbreviated n) 3

4 If the DNA gametes was not halved you would have twice as much DNA (genetic material) as your parents Sperm: sex cell/gamete that is a haploid cell Egg: sex cell/gamete that is always haploid Sex cells contain half of the diploid number these are called haploid cells Body cells are diploid they are called somatic cells So therefore if the haploid cell has ½ of the genetic material of a diploid cell, a diploid call has 2x the amount of genetic material in haploid cells Somatic cells: (diploid) body cells that are always diploid Some examples include nerve, muscle, liver and brain cells Body cells: somatic or diploid cells (2n) Humans have 46 chromosomes or 23 pairs of each body/somatic cell Any cell that contains two complete sets of chromosomes is called a diploid cell Allele: a version of alternative form of a gene (blue vs. brown eye) Homologous chromosome: one chromosome with genes (DNA) for the same traits, but with different combinations of alleles for those traits One homologous chromosome comes from you dad and one comes from your mom Mitosis Meiosis Form of reproduction Asexual Sexual Number of daughter cells Two Four Change in chromosome No change, number same as the Half of the original amount original Number of cell divisions One Two Difference in alleles between Exactly the parent cell and daughter cells same Completely different goes from diploid to haploid Genetics and probability o Probability is the chance that a particular event will occur o The principals of probability can be used to predict the outcome of genetic crosses Punnett square o The gene combinations that might result from a genetic cross can be determined by drawing a diagram called the Punnett square o The letters in the Punnett square represent alleles Capital letters represent a dominant alleles Lower case letters represent recessive alleles o Organisms that have two identical alleles for a particular trait are homozygous o Organisms that have two different alleles form one trait are heterozygous o Homozygous organisms are hybrid for a particular trait o Phenotype means the physical characteristics or outward appearance, something that you can take a picture of 4

5 o Genotypes are the genetic make up Probability/segregation o 3:1 is the ratio that resulted in Mendel s experiment (dominant : recessive) o There is segregation in Mendel s model Probabilities predict averages o Probabilities predict the average outcome of a large number of events o Probability cannot predict precise outcomes of and individual event o The larger the number of individuals the closer the resulting offspring numbers will get to the expected values o Ratios usually come very close to matching expectations Independent assortment o Two factor cross F 1 does not indicate whether genes assort or segregate independently however it provides the hybrid plants needed for the next cross o Independent assortment means genes that segregate independently For example, seeds shape and color do not influence each other s inheritance o The principal of independent assortment states that genes for different traits can segregate independently during the formation of gametes Summary of Mendel s principals o Inheritance of biological characteristics is determined by individual s units known as genes in organisms that reproduce sexually, genes are passed form parents to offspring o In cases which two or more forms of the gene for a single trait exist some forms of the gene may be dominant and others recessive o In most sexually reproducing organisms each adult has two copies of each gene and one from each parent, these genes are segregated from each other when gametes are formed o The alleles for different genes usually segregate individually from each other Beyond dominant/recessive alleles o Not all genes show simple patterns of dominant or recessive alleles in most organisms genetics are more complicated because the majority of genes have more than two alleles and many important traits are controlled by multiple alleles and genes Incomplete dominance o Incomplete dominance is when one allele is not completely dominant over the other o It has a heterozygous phenotype, and is somewhere between the two homozygous phenotypes Co-dominance o Co-dominance is when both alleles contribute to the phenotype of the organism Multiple alleles o Many genes have more than two alleles and are said to have multiple alleles o This does not mean that an individual can have more than two alleles but that more than two possible alleles can exist in a population Polygenic traits 5

6 o Polygenic traits are traits that are controlled by two or more genes meaning having many genes o Often shows a wide range of phenotypes Mendel s principals o Mendelian genetics can be uses to study the inheritance of human traits and calculate probability of traits appearing in the next generation More notes o Reginald Punnett developed the Punnett square This determines the probability of and offspring having a particular genotype o Phenotype rations are written as dominant : recessive o Genetics: the study of heredity o Heredity: the passing of traits to offspring o Allele: different forms of the same gene o Gregor Mendel Monk and horticulturist Referred to as the father of genetics o Mendel s methodology Used peas because of their short life cycle Controlled the breeding (not random) Counted a lot p peas Established and used purebreds o Traits: a characteristic that can be passed down from generation to generation o Purebred: can only produce offspring with one form of a trait o Mendel s law of segregation Each organism has two alleles for a gene, one from the mother one from the father The alleles separate when eggs of sperm are formed, each egg or sperm has one allele Sperm and eggs combine in predictable proportions o Genotype: an organisms genetic makeup o Phenotype: the expression of an organism s genetics o Zygosity: the similarity or difference between alleles for a trait o Homozygous: the allele for a trait are the same o Heterozygous: the allele for a trait are different o Dominant allele: allele that is expressed even when it is heterozygous o Recessive allele: allele that is expressed only when there is no dominant allele Gregor Mendel s peas o Segregation: allele pairs randomly separate during the formation of eggs and sperm and randomly come back together during fertilization o Independent assortment: different traits are inherited separately of each other o Law of dominance: if a homozygous dominant crosses with a homozygous recessive the offspring will always be heterozygous 6

7 The offspring will display the dominant phenotype and carry the recessive genotype Incomplete dominance o Incomplete dominance: cross between organisms with two different phenotypes producing offspring with a third phenotype Neither trait is dominant Represented by all capital letters Co-dominance o Hybrid organism shows third phenotype neither dominant nor recessive but rather mixed, nether of the alleles is dominant or recessive Both traits of a pair Fredrick Griffith o 1928 o Rough strain means that they will live o Smooth strain means that the mice will die o If you heat the smooth stain then the mice will live o Heat kills it-something transferred the traits to the R strain (some kind of genetic material) o Heated smooth strain mixed with the rough non-heated R strain will still kill the mice o Transforming material is passed from one type of bacteria to the other called genetic material Oswald Avery o 1944 o Asked what is the inheritance model o Destroyed lipids, ribonucleic acids, carbohydrates, and proteins in the virulent bacteria transformation still occurred o When he destroyed DNA transformation did not occur o DNA is therefore the molecule of inheritance Enwind Chargaff o 1952 o The mound of adenosine is equal to the amount of thymine o The amount of cytosine is equal to the amount of guanine Maurice Wilkins o Worked process DNA and prepared of X-ray studies o Helps develop helicase model in 1951 o Set up X-ray study lab photographed DNA with X-rays o Found that DNA was a helix and has rungs he improved the equipment James Watson and Francis Crick o Used Franklin s photograph 51 to accurately model the structure of DNA o Has a double helix with rungs o Won the Nobel prize in

8 o The rungs are held together with hydrogen bonds Avery o Avery and the other scientists discovered that DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next Hershey s experiment o Studied viruses o A virus that infects and kills bacteria known as bacteriophage or bacteria eater Composed of DNA/RNA core and protein coat Attacks and attached to the surface of a cell and injects DNA, the viral genes produce more bacteriophages and destroy bacteria o Hershey concluded that the genetic material of the bacteriophage they infected with bacteria was DNA, not protein Structure of DNA o DNA had to carry into from one generation to the next and put that information into work by determining the heritable characteristics of the organisms and be easily copied because all of the cells information is replicated every time a cell divides o Made up of units called nucleotides each made of three parts: 5 carbon sugar, deoxyribose A phosphate group And four nitrogenous bases Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Nitrogenous bases o Adenine and guanine are purines Have one ring smaller o Cytosine and thymine are pyrimidines Have two rings Bigger DNA structure o The backbone of DNA is made up of the sugar and phosphate o Nitrogenous bases stick out sideways and can be joined together in any order meaning any sequence of base is possible o Four different nucleotides can be strung together many different ways so that it can carry genetic information Chargaff s rules o Found that guanine and cytosine are equal in any sample of DNA o The same is true for adenine and thymine 8

9 X-ray evidence o X-ray diffraction is how we got information o We used this to get the scattering pattern of X-rays on film o X shaped patterns shows that the strands of DNA are twisted around each other like coiled of a spring or helix o Angle of the X suggests that there are two strands in the structure o The nitrogenous bases are near the center of the molecule Double helix o Watson and Crick s model of DNA was a double helix in which two strands were wrapped around each other o Hydrogen bonds could form between certain nitrogenous bases and hold the two strands together Form only between A and T and G and C Called base pairing o For every adenine in a double helix strand DNA molecule there had to be a T molecule for each C molecule there was a G molecule DNA o Deoxyribose Nucleic Acid o Functions include: Store/use info to direct activities of the cell (protein synthesis) Copy itself for new cells that are made o Made up of two long strands Helix (made of two) is the overall shape of the DNA Called the double helix Twirled ladder o Structure related to function o A nucleotide is three things that work as a unit: sugar, phosphate, and nitrogenous bases 5 carbon sugar, deoxyribose A phosphate group The four nitrogenous bases A purine and a pyrimidine match up in a double helix Two strands of nucleotides fit together to form a molecule of DNA DNA replication o 3 steps DNA helicase (enzyme) splits apart the two chains of DNA open areas are called replication bubbles or forks each strand acts as a pattern/template for the new strands DNA polymerase takes free nucleotides and makes new strands using Chargaff s rules 9

10 helps attract the nucleotide with the correct complementary bases along the new strand with the aid of DNA polymerase The enzymes double check new daughter strands for errors and fix anything if needed Sugar backbone bonds tightly Protein synthesis o 20 amino acids make proteins: 35-40,000 proteins o Proteins are catalysts that store, transfer, move, support, mediate cell responses, give immune protection, control growth, and cell differentiation o Made up of long chains of amino acids Structure determines function o Genes describe how to make proteins by putting the correct amino acids into a long chain in the correct order o Genes are in the nucleus on the chromosomes o RNA is used to carry messages of the code or genetic information RNA o Ribo Nucleic Acids o Has ribose instead of or deoxyribose as a sugar o Has uracil (U) instead of thymine (T) o Usually a single strand instead of a double o The job of RNA is to carry messages from the DNA in the nucleus to the ribosomes in the cytoplasm o There are three types of RNA Messenger RNA (mrna) From DNA to cytoplasm Transport RNA (trna) Transports amino acids to mrna to make a protein Ribosomal RNA (rrna) Makes up ribosomes with make up the protein o Process of gene to protein is called protein synthesis (the process of making proteins) that is divided into two parts Transcription Translation o Protein synthesis is the process of making DNA into proteins based on the code from DNA o Transcription: genetic information from a strand of DNA is copied into a strand of mrna o Translation: the mrna (with the help of the ribosome) forms a chain of amino acids (that will eventually form a protein) based on the information contained on the mrna o Order of events called the central dogma of molecular biology Transcription 10

11 o DNA unzips (enzymes split apart base pairs and unwind the DNA s double helix) o Bases pair up (free nucleotides to cell find their complementary bases along new strands) o New backbone formed (sugar phosphate backbone is assembled to complete the RNA strand and separated from DNA strand) Remember A=T and G=C o RNA editing And mrna molecule has to be edited in order to useful a lot of extra information needs to be removed An mrna sequence does not code for a proteins is called a intron A sequence that is useful in making a protein is called and exon Structure of RNA o Protein synthesis o Assembly of amino acids into proteins is controlled by RNA o Most genes contain instructions for assembly of amino acids into proteins o RNA molecules carry copies of these instructions also known as RNA messenger because they are messengers from the DNA to the rest of the cell o Proteins are assembled on ribosomes o Ribosomes made of several dozen proteins as well as a form known as ribosomal RNA o During construction of a protein a third type of RNA molecule transfers each amino acid to the ribosome as it is specified be coded messages in mrna known as transfer RNA Transcription o RNA molecules are produced by copying part of the nucleotide sequence into a complementary sequence in RNA a process called transcription o Requires an enzyme known as RNA polymerase that binds to the DNA and separated the DNA strands o RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA o RNA polymerase doesn t bind to DNA just anywhere o A promoter is and enzyme that binds only to certain parts of the DNA Have specific base sequences Signals in the DNA that indicate to the enzyme where to bind to make RNA similar signals in DNA cause transcription to stop when the new RNA molecule is completed RNA editing o Some of rrna molecules that makeup ribosomes are produced form larger RNA molecules that are cut to final sizes o Large pieces of are removed from the RNA molecules, transcribed from many eukaryotic genes before they become functional Known as introns/intervening sequences are cut out of RNA molecules until they are still in the cell nucleus 11

12 o Remaining portions are called exons/expressed sequences that tare then spliced in different ways in different tissues making it possible for a single gene to produce several different forms of RNA o Suggested that introns and exons may play a small role in evolution Makes it possible for small changes in DNA sequences to have dramatic effects in gene expression Genetic code o Proteins made by joining amino acids into long chains called polypeptides Each has a combination of any or all 20 different amino acids o Properties of proteins is determined by the order in which the different amino acids are joined together to produce polypeptides o The language of the mrna instructions if called the genetic code o RNA contains the bases A, U, C, and G therefore the doe is written in four different letters and is read with three of the different letters at a time (three bases) o mrna is known as the codon o a codon consists of three successive nucleotides that specify a single amino acid that is to be added to the polypeptide o because of the four different bases there are 64 possible three base codons o some amino acids can be specifies by more than one codon for example, 6 different codons code for the amino acid leucine, and 6 others specify for the amino acid arginine o AUG can either stand for methionine or serve as an initiation/ start codon for protein synthesis o There are three stop codons that do not code for any amino acid They are like the period at the end of the sentence it signals the end of the polypeptide Translation o Sequence of nucleotide bases in an mrna molecule serves as instructions for the order in which amino acids should be joined together to produce a polypeptide o Ribosome helps read the instructions o Decoding of an mrna message into the polypeptide chain (soon to be protein) is translation o Takes place in the ribosomes/cytoplasm o The cell uses mrna to turn the code into a protein o Process: Before translation can occur mrna must first be transcribed from DNA in the nucleus and released into the cytoplasm Begins when an mrna molecule in the cytoplasm attached to a ribosome, as each codon of mrna molecule moves through the ribosome the proper amino acid brought into the ribosome and attached to the growing polypeptide chain the 12

13 ribosome does not know which amino acid to match with each codon, that is the job of the trna (initiation) Each trna molecule has an amino acid attached to one and a region of three unpaired bases at the other three base on the trna molecule called the anticodon are complimentary to one of the mrna codons (matching) Like an assembly line worker who attaches on part to another the ribosome forms a peptide bond between the first and the second trna molecule and brings it the amino acid specified by the second codon (elongation) The peptide chain continued to grow until the ribosome reaches a stop codon is releases the newly formed polypeptide and the mrna molecule completing the process of translation (termination) Roles of RNA/DNA o DNA has all of the information in the nucleus o RNA makes disposable copies of the information to take to the cytoplasm and ribosomes Genetics/proteins o Genes have instructions for assembling proteins o Genes for certain proteins can regulate the rate of pattern of growth in and organism o Proteins are the enzymes that catalyze and regulate chemical reactions o Proteins are the keys to almost everything living cells so RNA sequence o Always starts with AUG, of methionine (codons) Other things you may need to know o The nucleotides in DNA are joined by covalent bonds o In DNA hydrogen bonds are easily broken so they can be easily split apart to replicate DNA o How DNA: Stores information: each strand or helix carries a sequence of nucleotides arranged almost like letters in the alphabet, allowing it to store information Copy information: the base pairs can be copied when hydrogen bods break and pull apart Transmit information: when DNA is copied the sequence of the base pairs is copied so genetic info can pass unchanged from one generation to the next Information about Rosalind Franklin and the structure of DNA o Died at age 37 o Went to Cambridge o Joined effort in research on coal, her experiments led to a better gas mask. o Has a Ph.D. o Her discovery that there were two forms of NDA is perhaps the most crucial step toward the discovery of its structure 13

14 o Watson and Crick wanted to build the structure of DNA by model building o Had to do many calculations by had to determine the structure of DNA o In May, 1952 she takes a great image of the B form of DNA labeled photo 51 From this photo you can see Number of units per turn per helical turn That it was in a helix o Unhappy at Kings receiving the nickname the dark lady o In photo 51 there was Each twist of the helix has 10 units of molecular building blocks Dimensions of image correspond to a helix of 34 angstroms per turn o Watson and crick could not have done it without Rosalind s important photo **note: some of this study guide may be repetitious. It is based off of sources from: Notes in class The power point currently on the website Handouts given in class Note takers given in class Quizzes Homework Notes from the book There is obviously going to be so repeats and overlap; I apologize. Also, there are probably many typos; I again apologize. I also recommend checking out the other power point cartoon; also on the website it is very helpful!!! Do not also think to just study this!!! Look at more handouts tests and quizzes notes the book and any other outside source that may be helpful. 14