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Biology 204 Principles of Biology I Assignment 2A For students with first names starting with the letters A to G. This assignment is graded out of 110 points, and is worth 10% of your final mark. Please submit this assignment after you have completed Chapter 16 and before you write the final exam. A Definition/Comparison Questions Instructions: In your own words , define the pairs of terms given below. Write in complete sentences, stating the differences and relationships between the two terms, and give specific examples where appropriate. A complete answer usually requires four to eight sentences. Each question is worth four marks, for a total of 40 marks. histones / chromatin Histones are associated with packaging of eukaryotic cells DNA at different levels of the organization. More accurately histones are small positively charged basic proteins that can associate with DNA because of their positive charge and DNA's negative charge. Histones and DNA interact in the chromosomes of eukaryotes, where the histones help in condensing the DNA into chromatin. Five histones types exist in the majority of eukaryotes: H1, H2A, H2B, H3, and H4, since there amino acids sequence is similar throughout eukaryotes, it is believed they perform the same functions. Functions of histones are to pack DNA
molecules into the cell nucleus and the regulation of DNA activity. Histones proteins are the what DNA wrap around to coil themselves to fit into a chromosome. Chromatin is directly influenced by histones since DNA and histones proteins make up chromatin. Chromatin takes two forms. The first form is called euchromatin which is less condensed and can be transcribed and the second form is heterochromatin which is highly condensed and is typically not transcribed. Chromatin looks like beads on a string; the beads are referred to as nucleosomes. The nucleosomes are composed of DNA which is wrapped into 30 nm spirals called solenoid, and additional histones proteins support chromatin structures. The function of chromatin is to package DNA, so it will fit in the nucleus and also protect the DNA sequence and structure. By DNA being packaged into chromatin, mitosis and meiosis can occur, gene expression and DNA replication are controlled, and chromosome breakage is prevented. chromatin is the material that makes up the content of the nucleus in eukaryotes; consists of two parts: proteins (of which the histones are a major component) and DNA 4 / 4 linkage / independent assortment Linkage and independent assortment are both related to
genes behavior and learned that genes assorted independently. Since chromosomes act independently of each other during meiosis, the genes on each chromosome also assorted independently in the gamete formation. Although, genes that were on the same chromosome and were not assorted independently, meaning during meiosis the chromosome was inherited as single. Therefore these genes are known as linked genes which are referred to as linkage. Linkage was tested on Drosophila (fruit fly), it was reasoned that genes sitting farther apart from each other would have a better chance to separate from each other compared to independent assortment which shows that genes that are farther apart from each other or on different chromosomes with have a recombination frequency of 50%. Mendel's Law of independent assortment states that alleles of two different genes will be sorted to gametes independently of each other. Although, if the genes did not follow Mendel's law of independent assortment the genes would always be inherited as a pair. 4 / 4 autosomes / Y chromosome Autosomes and Y chromosomes are both involved in human genetics. Autosomes are chromosomes found in eukaryotic cells but are not sex chromosomes. Humans and animals
have two types of chromosomes:
deoxyribose sugars that are linked to phosphate groups, following the pattern sugar-phosphate-sugar phosphate which forms the sugar- phosphate backbone. The phosphates make up the bridge between the 3' carbon of one sugar and 5' carbon of the next sugar. The phosphodiester bond is phosphorus involved in two ester bonds. The DNA strands in the double helix are made up of nucleotides that connect to form a chain that is linked by a phosphodiester linkage. The double helix has an exterior sugar- phosphate backbone that is held together by strong covalent bonds compared to the interior hydrogen- bonded base pairs that have a weak hydrogen bond. The physical characteristics of the double helix are two polynucleotide chains that are twisted around each other, similar to a double- spiral staircase. The hydrogen bonds between the base pairs hold the backbones together. The double helix has 10 base pairs per turn of the helix, the polynucleotide chains are antiparallel, each full twist is 3.4nm, the distance between base pairs is 0.34nm, and there are two base pairs: nucleotide A pairs with T, and nucleotide C pairs with G. Phosphodiester linkage and double helices are work closely together with DNA, and each other. The phosphodiester linkage bonds the DNA'S nucleotides to form the polynucleotides that are used to make up the double helix, one cannot exist without the other. 4 / 4
Adenine/Thymine Adenine C5H5N5 is one of four nitrogenous bases that is found in DNA and RNA that helps in stabilizing the nucleic acid part of the atoms and molecules. Thymine C5H6N2O2 is also one of four nitrogenous bases found only exclusively in DNA. Thymine is made up of one nitrogenous base that is different from adenine; it also contains one phosphate group and one deoxyribose. Adenine is a purine base which has a double ring form, while thymine is a pyrimidine base that has a single ring form. Adenine and thymine will be partners for DNA and will come together to form AT. Thymine which is only found in DNA is the main stabilizer for DNA and will only bind with adenine followed by two hydrogen bonds to stabilize that area on the DNA ladder. Adenine is found in ATP; when the adenine base connects with a ribose and chain of three phosphates, ATP is formed. Since thymine is not present in RNA adenine pairs with uracil. 4 / 4 exons / pre-mRNA Exons are an amino acid nucleotide sequence found in finished mRNA that comes after the pre-mRNA. mRNA splicing in the spliceosome is involved in joining of two exons and is so exact that not a single exon base is removed. Under certain conditions, exons may be joined to form different combinations producing different mRNAs from a DNA sequence
of the most crucial tools in molecular biology. PCR is unique because it replicates just a portion of the DNA polymerase instead of the entire molecule. The PCR has four fundamental elements: DNA, DNA primer pairs, four nucleoside triphosphate, and DNA polymerase, since the PCR uses high temperature sometimes. DNA cloning is the production of identical copies of DNA fragments, the clone which is a genetically identical replication of its ancestor is used by scientists to focus on a gene of interest. Scientist clone specific genes to study them or alter their function, so that the altered gene can become a pest-resistant plant. DNA cloning has a special process to create the replica, scientists must isolate the gene they want and the bacterial plasmid that is used as the carrier. Along with bacterial cells, yeast cells and mammalian cells can also be used as carrier cells for DNA cloning. The desired piece of DNA is removed by restriction enzymes and put into the bacterial plasmid using DNA ligase. Recombinant DNA plasmids using bacteria are most optimal since they pass genetic information from generation to generation. Human scientist has had success with cloning farm animals; the first successful cloning was of Dolly, the sheep. 4 / 4 Posttranscriptional regulation / translational regulation (re: eukaryotes) Posttranscriptional regulation comes after transcriptional regulation, which determines the genes that are copied to mRNAs. Posttranscriptional regulation is responsible for translation by controlling
ribosomes of the mRNAs. Posttranscriptional are also known for masking proteins for control, regulating pre-mRNA processing, the rate at which mRNAs degrade and, the availability of mRNA for translation. Translational regulation which is also an of gene expression is the next step after posttranscriptional regulation. Translational regulation controls the rate at which mRNAs will be used in protein synthesis, and will occur in basically in all cells and control cell cycle in eukaryotes. For the translation process to occur a eukaryote protein initiation factor-2 must attach to the ribosome. When the EIf-2 is turned off it is phosphorylated so translation cannot begin and when it is on it is not phosphorylated, so initiated so translation can proceed. 4 / 4 tRNA / rRNA Transfer RNA is a specialized RNA molecule because it brings the amino acids to the ribosomes, where the proteins are constructed. This form of RNA is a part of the nucleic acid group referred to as ribonucleic acids that are made up of nucleotides. tRNA has the specific job of translating messages from nucleic acids/nucleotides into amino acids or proteins. TRNA in eukaryotic cells is made of a special protein that will read the DNA sequence and continues to make then RNA, or pre-tRNA which will only be processed when it leaves the
that essential in regulation, coding, decoding and gene expression. rRNA is a part of the ribosomes and is found in both eukaryotes and prokaryotes.
Full answer:
two main types of RNA; transfer RNA and ribosomal RNA tRNA is single stranded but loops and base pairs into a three dimensional structure contains a specific anticodon and binds to one specific amino acid at its 3' end it carries its amino acid to the A site of the ribosome and base pairs with its respective codon on the mRNA as it moves to the P site its AA binds to the polypeptide chain rRNA is the main constituent of the ribosomes, together with proteins lysogenic cycle / lytic cycle The virus infects cells by taking over host cells and proceeding to replicate very quickly, once the virus is ready to replicate it can choose so by either the lysogenic cycle or lytic cycle. Lysogenic cycle refers to a certain way that viruses choose to replicate, where the virus duplicates a few virus copies at a time and does not kill the cell, whereas, lytic cycle duplicates millions of copies until the cell burst open due to the pressure killing the host cell. Once the lysogenic virus attacks a host cell, it puts its genome into the nucleus of the host cell, where the genome then bonds to the host cells genome. The lytic cycle follows four
steps in creating new virus cells: it infects a host cell, infects the host with virus material, creates new virus cells using host cells metabolic engines and virus cells explode out of infect host cell. Full answer: terms refer to the life cycle of viruses the lytic cycle refers to virulent bacteriophages that kill their bacterial host cells in each cycle they inject their DNA into a bacterium which when expressed degrades the bacterial DNA and reproduces virus DNA and capsids at the end of the cycle newly synthesized bacteriophages are released from the dying bacterium occasionally pieces of the degraded bacterial DNA are by mistake packed into a virus body, this leads to generalized transduction in the lysogenic cycle viral DNA is integrated into the bacterial DNA and the bacterium is not killed: temperate bacteriophages the bacterium with the prophage can enter many cycles of binary fission which also reproduces the prophage. Under particular environmental conditions the prophage releases itself from the bacterial DNA and starts a lytic cycle killing the unfortunate bacterium specialized transduction 3.5 / 4 A = 38 / 40 B Short Answer/Short Essay Questions
1. Describe the major phases of the cell cycle in a typical eukaryote. The major phases of the cell cycle in a typical eukaryote cell or any cell that possess a nucleus will be divided into two main phases: interphase and mitotic phase. These phases together
original parent cell being split into two new daughter cells. The first part of the process called interphase involves the cells growth. Accumulation of nutrients needs for the next phase which is mitosis, and the duplication of DNA. Interphase is broken into three phases: G1, S, and G2 phase, where G1 is the longest of the three. Next, the M phase is where cell division occurs, the M phase is divided into processes, the first part is where the chromosomes are divided between two sister cells and the next part is cytokinesis where the cytoplasm of the cell divides in half forming to individual new cells. 7 / 7
2. Which major event during meiosis is most likely to produce deviations from Mendel’s laws? The major event that will produce deviations from Mendel's law is if during meiosis the crossing over of two homologous chromosomes does not occur. Crossing over would occur during prophase one of meiosis where the chromosomes would come together to form a tetrad structure where a segment of genetic material from each chromosome is exchanged. If the chromosomes do not cross over (exchanging their genetic information from each parent), the haploid will only inherit a chromosome with the same information of alleles as the parent chromosome, therefore the genes are not altered. When crossing over
actually occurs the haploids cells after meiosis has four possible genetic outcomes that agree with Mendel's laws. Referring to Mendel's second law, the law of independent assortment; genes for different segregate independently during gamete formation. Segregation of alleles may be influenced by the linkage which is when genes are located close to each other on the same chromosome, therefore are more likely to be inherited as a pair. Therefore, if crossing over did not take place the alleles on the same chromosome would remain linked and not assorted independently. Examples can be seen of this in the crossing over may involve linked genes, if they are close together on the same chromosome 1 / 2
3. Explain, with examples, the concept of jumping genes in prokaryotes. (5 marks) Jumping genes referrers to DNA sequences that move from one area of the genome to another. Also, know as mobile elements since they can move their DNA backbones using a special form of recombination that can function without homology. Jumping genes or mobile elements are also known by the term "transportable elements" (TEs), along with the term "transposition" that refers to their way of moving. The form of moving can occur at low
4. Explain the variation of blood types in humans. The human blood group, ABO, was discovered by Karl Landsteiner who made the discovery of how only mixing certain blood types was successful. That was determined by the antigens of the different blood types that was made up of carbohydrate parts of glycoproteins that were found the red blood cell. Therefore, the variation of blood types in humans is determined by the antigens on our red blood cells. The antigens are genetically decided and have evolved. The four types of blood we know today: A, B, AB, and O. The types are determined by the presence of A , B , antigens on red blood cells. Type A blood means the red blood cells have an A antigen, and Type B would mean the red blood cells have a B antigen. Type AB occurs when both A and B antigens are present, and Type O is the absence of A and B antigens. Full answer: AB0 blood types: multiple alleles I gene can be IA, IB, or i A blood group may be IA^ IA^ or IAi B blood group may be IBIB or IBi AB is IA^ IB 0 is ii 3 /
