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Unit 4 Topic 1
DNA, Genes and the Continuity of Life
| Question | Answer |
|---|---|
| Where is DNA found in eukaryotic organisms? | DNA can be found in the nucleus, mitochondria and choloroplasts. |
| What is the role of DNA helicase? | Helicase is the enzyme unwinds (unzips) the DNA double helix by breaking the hydrogen bonds between nucleotides, thus, exposing the nitrogen bases. |
| What is the role of DNA polymerase? | DNA polymerase is the enzyme that joins the new nucleotides to form a new complementary strand of DNA. These nucleotides are linked in a 5' to 3' direction. |
| Describe the structure of DNA. | DNA is helix-shaped molecule composed of two long strands of subunits called nucleotides. A nucleotide is composed of a 5-carbon sugar (deoxyribose), a negatively charged phosphate group and a nitrogen base. Bases are connected by hydrogen bonds. |
| What are the four nitrogen bases? | Adenine, thymine, guanine and cytosine. |
| Why is DNA replication referred to as semi-conservative? | Because the outcome of DNA replication is two double helix DNA molecules, each consisting of one parental strand and one new strand. This means that from one generation to the next, DNA is being conserved. |
| Describe the process of DNA replication. | DNA helicase 'unzips' the double-stranded DNA by breaking the hydrogen bonds between nucleotides, exposing the bases. Free nucleotides attach to exposed bases and DNA polymerase joins them together to form new complementary strands. |
| What is the purpose of DNA replication? | To prepare the cell for cell division for growth, repair and reproduction |
| What is the product of meiosis? | Meiosis results in the formation of four haploid daughter cells. |
| Where does meiosis occur? | In mammals, meiososis occurs in the ovaries and testes. In plants, meiosis occurs in the male and female parts of flowers. |
| What happens during interphase? | DNA replication occurs during interphase. |
| What is process in Meiosis I referred to as? | reduction division (2n --> n) |
| What is the process in Meiosis II referred to as? | separation division (n --> n) |
| What are the 4 stages of Meiosis I? | prophase I, metaphase I, anaphase I, telophase I and cytokinesis |
| What are the 5 stages of Meoisis II? | prophase II, metaphase II, anaphase II, telophase II and cytokinesis |
| What happens in prophase I? | Centrioles start migrating to the poles and spindle fibres start forming. Synapsis occurs: bivalent chromosomes condense and align in tetrads. Chromatids entwine and chiasmata can form. The nuclear membrane begins to break down. |
| What happens in metaphase I? | Homologous chromosomes independently assort and align themselves along the equator of the cell. |
| What happens in anaphase I? | spindle fibres draw maternal and paternal chromosomes of homologous pairs to opposite poles. *This disjunction occurs independently |
| What happens in telokinesis I? | The spindle fibres break down and new nuclear envelopes form around the two new nuclei. |
| What happens in cytokinesis? | The cytoplasm divides. |
| What happens in prophase II? | A new spindle forms and attaches to centromeres. |
| What happens in metaphase II? | chromosomes align along the equator of the cell (equatorial plate) |
| What happens in anaphase II? | the centromere splits, separating sister chromatids which then move to opposite poles. |
| What happens in telophase II? | spindle fibres break down, and the chromosomes de-condense to their thread-like form. New nuclear envelopes form. cytokinesis occurs, resulting in the formation of four haploid cells. |
| What is it, and when does crossing over and recombination occur? | Crossing over is when homologous chromosomes exchange segments with one another. It occurs during synapsis in prophase I when chromosomes entwine and form chiasmata. |
| What is the effect of crossing over? | Crossing over increases the genetic variation within the offspring as it scrambles pieces of maternal and paternal DNA creating new allele combinations. |
| What is oogenesis? | Oogenesis is the process in the ovary that results in the production of femal gametes (Ovum) |
| What is spermatogenesis? | Spermatogenesis is the continuous production of sperm cells in the testis |
| What are the key differences between oogenesis and spermatogenesis? (3) | 1. In oogenesis, cytokinesis is unequal = produces one viable egg Spermatogenesis = four sperm. 2. An ovary contains all eventual eggs at birth. Males produce sperm continuously throughout their life. 3. sperm=continuous, oogenesis = long breaks between. |
| What are similarities between oogenesis and spermatogenesis? | Both produce haploid cells (2n --> n) |
| What is independent assortment? | Independent assortment is the process where the paternal and maternal chromosomes of each homologous pair behave independently of the other pairs when separating in meiosis. |
| What is random fertilisation? | random fertilisation is when any egg is fertilised by any sperm. |
| How does independent assortment and random fertilisation contribute to genetic diversity? | Independent assortment ensures all haploid cells contain both maternal and paternal DNA --> increases the number of possible gene combinations. Random fertilisation increases genetic variability as increases the possible chromosome combinations. |
| What is a genome? | A genome is all of the genetic material carried within an organism or a cell. |
| What is the role of genes? | Genes 'direct' the production of polypeptides that make up proteins, or of RNAs involved in the synthesis of proteins. |
| There are 2 types of genes or DNA included in this. | Coding and non-coding |
| What is a codon? | A codon is a triplet of bases that codes for an amino acid. |
| What are the four differences between DNA and RNA molecules? | 1. DNA = deoxyribose sugar. RNA = Ribose sugar 2. DNA = double-stranded. RNA = single-stranded 3. DNA = C-->G and A-->T. RNA = C-->G and A-->U 4. DNA is longer than RNA. RNA is much shorter than DNA. |
| DNA molecules act as templates for _____ | messenger RNA (mRNA) |
| What is transcription? | Transcription is the formation of an mRNA molecule from a template strand of DNA in the nucleus by complementary base pairing. |
| What are the four universal structural features in a gene? | Start and stop triplets, promoter regions, exons and introns. |
| What are the three stages of transcription? | 1.Initiation. 2. elongation 3. termination |
| Protein synthesis 2 processes. what are they? | Transcription of gene into messenger RNA in the nucleus. Translation of mRN into an amino acid sequence at the ribosome. |
| Describe the process of initiation in transcription. | Transcription factors combine with the promoter region RNA Polymerase attaches to the promoter, unwinding and unzipping the DNA molecule by breaking the hydrogen bonds between the two strands to expose the bases. |
| Describe the process of elongation in transcription. | The RNA Polymerase moves along the DNA molecule, producing a strand of mRNA. by using a strand of DNA as a template, and attaching nucleotides (A, U, G, C) by complementary base pairing. |
| Describe the process of termination in transcription. | RNA Polymerase reaches the termination site of the gene (STOP codon) and translation ends. The RNA Polymerase detaches, releasing mRNA and allowing the DNA molecule to reform. |
| What are the three steps that happen during RNA processing? | addition of a 5' cap, addition of a poly-A-tail and splicing (removal) of introns |
| Describe the process of adding a 5' cap during RNA processing. | During transcription, a 5' cap (methylguanosine triphosphate molecule) is added to the 5' end of the pre-mRNA |
| Describe the process of adding a poly-A-tail during RNA processing | After transcription, a chain of 250adenine nucleotides is added to the 3' end of the pre-mRNA |
| What does the addition of a 5' cap and poly-A-tail do? | The addition of a 5' cap and a poly-A-tail increases the stability of the mRNA, stopping it from degrading. THe 5' cap also helps the ribosome bind to the mRNA |
| Describe the process of splicing during RNA processing? | Splicing removes the introns from the pre-mRNA transcript to form mature mRNA. During splicing, a molecule called spliceosome removes introns and joins extron sections together. |
| What is translation? | translation is the joining of amino acids in a specific order, according to the codons of the mature mRNA as 'read' by a ribosome to form a protein. |
| Describe the process of initiation in translation? | A ribosomal subunit recognises the 5' cap and binds to the mRNA, moving along the RNA until reaching a start codon. A tRNA binds to the start codon (complementary base pairing) causing a large ribosomal subunit to attach to the tRNA and small subunit. |
| What are the three binding sites formed at the end of initiation in translation? | A - aminoacyl, P - peptidyl and E - exit sites. |
| Describe the process of elongation in translation? | After the attachment of methionine, another tRNA w a complementary anticodon to the next codon in the mRNA binds/attaches its accompanying amino acid to the growing protein chain via a peptide bond. the ribosome releases 'empty' tRNA, moving along mRNA |
| Describe the process of termination in translation? | Attachment of the amino acids continues until a stop codon is reached. The protein releases from the ribosome into the cytoplasm or ER. mRNA is broken down and recycled. |
| What is coding DNA? | coding DNA is the small part of DNA used as a template for mRNA synthesis; gene |
| What is non-coding DNA? | all DNA sequences within the genome that are not found within mRNA-coding exons. |
| What is the purpose of gene expression? | to produce RNA molecules for polypeptides; protein synthesis |
| What are the two main categories of gene regulation? | Short-term regulation and long-term regulation |
| Describe two chemical modifications of chromatin at transcription stage. | Histone acetylation of histone protein tails loosens the DNA's associations with the histones (acetylation = transcription on) Methylation results in gene inactivation by strengthening the attraction between DNA and histones (= transcription off) |
| Describe direct chemical modification of DNA at transcription. | Methylation and acetylation also occur directly to chromosomal DNA. The addition (by kinases) and removal (by phosphatases) of phosphate groups to DNA also acts to regulate transcription. |
| What are transcription factors? | regulatory proteins whose function is to activate or inhibit transcription of coding DNA by binding specific non-coding segments near the gene to be expressed or repressed. |
| What is the role of activators (gene expression)? | activators assist the binding of RNA Polymerase to begin transcription. |
| What is the role of repressors (gene expression)? | repressors bind to a specific region on the DNA preventing RNA Polymerase from binding |
| How do environmental influences impact gene expressions? Example? | Identical twins have the same genome but often show different characteristics such as height and weight. Eg. Himalayan Rabbit - fur turns black in the cold and white in the heat. Has the same genome. |
| What is epigenetics? | epigenetics is the study of heritable chemical modifications to gene function that are not due to changes in DNA sequences |
| What is a homeobox gene? | A homeobox gene is a gene of a group that code for proteins that regulate body formation and patterning in the developing embryo. Homeobox proteins are regulatory proteins. |
| What is the role of the Y chromosome in sex determination? | Y chromosomes contains SRY (sex-determining region of the Y chromosome) ---> Y chromosome = male characteristics --> no Y chromosome = female |
| What is an example of a transcription factor gene that regulates morphology? | Hox genes. Eg. Bicoid protein in fruit flies. |
| When can mutations occur? | Mutations can occur during DNA replication or cell division. They can also occur as a result of exposure to mutagens |
| What are the three categories of mutations that are usually detected and repaired by enzymes? | Beneficial mutations. Harmful mutations and neutral mutations. |
| What is a somatic mutation? | A somatic mutation occurs in body cells and can only affect the invidual in which they arise. |
| What is a germline mutation? | Germline mutations occur in the gametes and can be passed on to the organisms offspring. |
| What is a point mutation? | A point mutation is a mutation that arises from the alteration of a single base --> also known as SNIPs (single nucleotide polymorphisms) |
| What are the three tyes of Point mutations? | Silent mutations. Missense mutations. Nonsense mutations. |
| What is a silent mutation? (type of point mutation) | A silent mutation is where there is a substitution of one nucelotide base that does not change the amino acid sequence. Silent mutations have no effect. |
| What is a missense mutation? (type of point mutation) | A missense mutation is where one base in a codon changes and a different amino acid is produced. These are also known as synonymous mutations or substitution mutations. |
| What is a nonsense mutation? (type of point mutation) | a nonsense mutation occurs when (occasionally) a single base mutation results in a stop codon and premature termination of translation. The shortened polypeptide chain may or may nor be functional |
| What is a frameshift mutation? | A frameshift mutation is the insertion or deletion of a single or non-multiple of the three nucleotides in the DNA (indel). This type of mutation dislocates the translational reading frame --> all codons downstream of indel are affected. |
| What are spontaneous mutations? | spontaneous mutations arise randomly as natural mutations in the DNA base sequence. They are rare and unrepaired errors in DNA synthesis |
| What are induced mutations? | Induced mutations are mutations that arise as a result of exposure to mutagens. |
| What are the three types of induced mutations? | Physical Chemical Biological |
| What are chemical mutations? | Chemical mutations arise due from exposure to chemicals - some are mutagens, some are carcinogens. Often arise as a result of changing agricultural and industrial practices and warfare. |
| What are biological mutations? | Biological mutations arise from bacteria and viruses which change the genetic composition of cells by integrating their own DNA into the human genome during cell division. |
| What are physical mutagens? | Physical mutagens: ionising and non-ionising radiation -->the energy carried disrupts atoms in DNA sequence. UV radiation --> mutagenesis; skin cancer. X rays cause 'gaps' in the double helix. Nuclear radiation --> doublestranded breaks in chromosomes |
| Explain heat as a mutagen. | When DNA is exposed to heat, the bond that links the nitrogen base to the sugar can break --> leaves a baseless site in the DNA. The sugar-phosphate site then degrades leaving a gap in the DNA template. |
| What are block mutations? | Block mutations are mutations that affect large sections of chromosomes. These occur during meiosis or from mutagens. |
| What are the five types of block mutations? | Duplication Deletion Inversion Insertion Translocation |
| What is a duplication block mutation? | A section of the chromosome is replicated, resulting in multiple copies of the same gene. |
| What is a deletion block mutation? | Sections of the chromosome are removed --> disrupted or missing genes |
| What is a inversion block mutation? | Section of the chromosome breaks, rotates 180* and reattaches to the same chromosome. |
| What is a insertion block mutation? | Section of the chromosome breaks of and attaches to another chromosome |
| What is a translocation block mutation? | A whoe chromosome or segment of a chromosome becomes attached to or exchanges with another chromosome or segment |
| What is non-disjunction? How does it lead to aneuploidy? | Non-dusjunction is where chromosomes fail to separate correctly during meiosis. This results in an abnormal number of chromosomes in the daughter cells --> aneuploidy. |
| Identify 3 syndromes that result from aneuploidy. | Down Syndrome --> trisonomy: 3 copies on a chromosome present (47) Klinefelter Syndrom --> extra X chromosome (47) Turner Syndrome --> all or part of one X chromosome is altered/missing. Misonomy (45 complete) |
| What are Mendel's 3 rules of heredity? | 1. Principle of Dominance --> recessive alleles are masked by dominant alleles. 2. Law of segregation --> each gamete carries only one allele for each gene. 3. Law of independent assortment --> segregation occurs independently |
| What is the law of probability for predicting inheritance? | The chance of two independent events occurring together is equal to the chance of one event occurring alone multiplied by the chance of the other event occurring alone. |
| What is polygenic inheritance? | Polygenic inheritance is where the transmission of a single trait is controlled by 2 or more genes. Eg. Human height and corn cob length. |
| What is biotechnology? | Biotechnology is the use of living organisms and biological systems and processes for human benefit |
| What is recombinant DNA technology? | the process of transferring a gene from a cell of a member of one species to the cell of a different species. |
| What are the four main steps in creating recombinant DNA? | 1. isolation of DNA and cutting of DNA (restriction enzymes) 2. Insertion of DNA fragment (plasmid vector) 3. Joining of DNA (DNA ligase) 4. Amplification of recombinant DNA (bacterial transformation) |
| Explain the first step of making recombinant DNA. (isolation and cutting) | The DNA of interest is isolated from the donor organism. Restriction enzymes are used to cut DNA at specific base sequences. 2 pieces of DNA (plasmid DNA and DNA of the gene) are cut with the same restriction enzyme so that they have matching sticky ends. |
| Explain step two of making recombinant DNA (insertion of DNA/plasmid vector). | The plasmid vectors and the gene of interest are mixed together and their sticky ends pair (annealing) |
| Explain the third step of making recombinant DNA (DNA ligase). | The two fragments of DNA are then joined together by DNA ligase, producing a molecule of recombinant plasmid DNA |
| Explain the fourth step of making recombinant DNA (bacterial transformation). | The recombinant plasmid DNA is added to a bacterial culture where transgenic bacteria will take up the plasmid from solution via transformation. When bacteria reproduce and replicate, copies of the recombinant DNA is are also produced |
| What is annealing? | Annealing is the process where fragments of DNA with matching sticky ends join via base-pairing. |
| What is polymerase chain reaction (PCR)? | a cyclic reaction in which DNA polymerase is used to copy a DNA template, making millions of copies of the same piece of DNA. |
| What are the three steps of PCR (polymerase chain reaction)? | 1. Denaturation 2. Annealing 3. Extension |
| Describe the process of denaturation in PCR | The double-stranded DNA is heated to 95*C, breaking the hydrogen bonds between the bases, thus causing the two strands to separate. |
| Describe the process of annealing in PCR | The temperature is reduced to 50-60*C enabling the formation of hydrogen bonds in the base-pairing. The primers anneal to complementary sequences on opposite ends of each strand. |
| Describe the process of extension in PCR | the temperature is raised to 72*C (optimal for DNA polymerase). Starting at the primers, DNA strands are synthesised using DNA polymerase and available nucleotides. At the end of extension, there are two copies of the double stranded DNA. |
| What is gel electrophoresis? | Gel electrophoresis is a technique that separates DNA fragments according to their size and charge. |
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Caitlyn_01
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