Unit 4: Building blocks of Life Part 2 Flashcards
Includes: DNA, Meiosis and genetics, Natural selection and evolution, and Introduction to biotechnology. (36 cards)
Describe the experiments that lead to the identification of nucleic acid as the genetic information carrier
19th century: Observations of Mendel and others indicate the genetic material is contained in cells.
1928: Frederick Griffith demonstrated the transmission of genetic instructions by a process we now call the ‘transformation principle’.
1944: Avery, MacLeod and McCarty suggest DNA is the ‘transforming factor’, and not proteins or other materials.
1952: Hershey and Chase proved that DNA was the genetic material in bacteriophage
Describe the central dogma of molecular biology
The central dogma of molecular biology is an explanation of the flow of genetic information within a biological system. it states that information can be transferred from DNA to RNA, from DNA to protein, or from DNA to protein, but not from protein to nucleic acid or protein.
Define the structure of a nucleotide as the monomer from which nucleic acids are made
Nucleotides serve as the monomer units for forming the nucleic acid polymers of DNA and RNA. Nucleotides are composed of three subunit molecules: nitrogenous base, five-carbon sugar, at least one phosphate group. A five-carbon sugar molecule attached to a nitrogenous base is called a nucleoside.
Describe the structure of DNA and RNA and define the differences between their structures
DNA: replicates and stores genetic information. Consists of two strands, arranged in a double helix, made up of nucleotide subunits. Longer polymers than RNA(E.g. a chromosome is a single DNA molecule, millions of bases). The sugar in DNA is deoxyribose. The bases in DNA are Adenine, Thymine, Guanine, and Cytosine.
RNA: Converts the genetic information contained within DNA to a format used to build proteins. Only has one strand, but like DNA, is made up of nucleotides. Variable in length, but typically quite short(E.g. mRNAs 100’s-1000’s bases). The sugar in RNA is ribose. The bases in RNA are Adenine, Uracil, Guanine and Cytosine.
Explain how the functions of DNA emerge from the structure of its monomers and its antiparallel, double helical and three-dimensional strucutre
Structure: Polynucleotide chains have nitrogenous bases linked to a sugar-phosphate backbone. Nucleotides are linked by phosphodiester bonds(C-O-P-O) to form a DNA strand. Phosphodiester bonds of the DNA give the polarity of the DNA strand(5’ phosphate and 3’ hydroxyl end).
Double helix: hydrogen bonds between the bases of the opposite strands and base stacking of bases within a strand contribute to the stability of DNA double helix. Phosphodiester bond of the backbone is also relatively stable. dsDNA can withstand stress like heat and pH.
Describe how a DNA molecule is replicated(semi-conservative DNA replication)
The basic principle of replication is base pairing to a template strand. Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication. In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules.
Semi conservative: Parental molecule–> separation of parental strands into templates–> Formation of new strands complementary to template strands. Semiconservative model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand(‘conserved’ from the parent molecule) and one new strand. Competing models were the conservative model(the two parent strands rejoin after replication), and the dispersive model(each strand is a mix of old and new).
Explain how genetic information is provided for protein synthesis and define the genetic code
The information content of genes is in the specific sequences of nucleotides. The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. DNA must be replicated for cells to divide. Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation.
Genetic code: the means by which DNA and RNA molecules carry genetic information in living cells
Describe transcription
RNA is the bridge between genes and the proteins for which they code. Transcription is the synthesis of RNA using information in DNA. Transcription produces mRNA for protein-coding genes. RNA polymerase is the primary enzyme of transcription.
DNA unwinds and RNA polymerase binds the appropriate ribonucleotides. RNA polymerase synthesises mRNA. When RNA polymerase reaches the end of the gene it releases the mRNA and DNA rewinds.
The stretch of DNA that transcribed is called a transcription unit. it includes a promoter, an RNA-coding region, and a terminator. RNA polymerase binds and initiates transcription at the promoter.
Initiation: Various transcription factors mediate the binding of RNA polymerase and the initiation of transcription. The completed assembly of transcription factors and RNA polymerase bound to a promoter is called a transcription initiation complex. A promoter element called a TATA box is crucial in forming the initiation complex in Eukaryotes.
Elongation: As RNA polymerase moves along the DNA, it untwists the double helix, 10-20 bases at a time. Transcription progresses at a rate of 40 nucleotides per second in eukaryotes. A gene can be transcribed simultaneoulsy by several RNA polymerases. Nucleotides are added to the 3’ end of the growing RNA molecule(5’ to 3’).
Termination: The mechanisms of termination are different in bacteria and eukaryotes. In bacteria, the polymerase stops transcription at the end of the terminator sequence and the mRNA can be translated without further modification. In eukaryotes, RNA polymerase transcribes the polyadenylation signal sequence; the RNA transcription is released 10-35 nucleotides past this polyadenylation sequence.
Last: Explain the role of mRNA processing in eukaryotic gene expression
Like prokaryotic cells, the transcription of genes in eukaryotes requires the actions of an RNA polymerase to bind to a sequence upstream of a gene to initiate transcription. However, unlike prokaryotic cells, the eukaryotic RNA polymerase requires other proteins, or transcription factors, to facilitate transcription initiation.
Understand the main stages of meiosis
Meiosis 1: Prophase 1: the chromosomes condense and homologous chromosomes pair up to form tetrads
Meiosis 1: Metaphase 1: the tetrads are all arranged at the metaphase plate.
Meiosis 1: Anaphase 1: the homologous chromosomes separate and are pulled toward opposite poles.
Meiosis 1: Telophase 1: movement of homologous chromosomes continues until there is a haploid set at each pole.
Cytokinesis by the same mechanisms as mitosis usually occurs simultaneously.
Meiosis 2: Prophase 2: a spindle apparatus forms, attaches to kinetochores of each sister chromatids, and moves them around.
Meiosis 2: Metaphase 2: The sister chromatids are arranged at the metaphase plate.
Meiosis 2: Anaphase 2: the centromeres of sister chromatids separate and the now separate sisters travel toward opposite poles.
Meiosis 2: Telophase 2: separated sister chromatids arrive at opposite poles.
Cytokinesis separate the cytoplasm.
At the end of meiosis, there are four haploid daughter cells.
Explain the significance of meiosis in life cycles
A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism. It starts at the conception of an organism until it produces its own offspring.
Explain how meiosis and fertilisation can lead to variation through the independent assortment of alleles
In humans, each somatic cell(all cells other than sperm or ovum) has 46 chromosomes, 23 homologous pairs. We inherit one chromosome of each homologous pair from each parent. The 46 chromosomes in a somatic cell can be viewed as two sets of 23, a maternal set and a paternal set. These homologous chromosome pairs carry genes that control the same inherited characters. As an organism develops from a zygote to a sexually mature adult, the zygote’s genes are passed on to all somatic cells by mitosis. Gametes, which develop in the gonads, are not produced by mitosis. If gametes were produced by mitosis, the fusion of gametes would produce offspring with four sets of chromosomes after one generation, eight after a second and so on. Instead, gametes undergo the process of meiosis in which the chromosome number is halved. Human sperm or ova have a haploid set of 23 different chromosomes, one from each homologous pair.
Use genetic diagrams to solve problems including sex linkage and codominance
Codominance: two dominant alleles affect the phenotype in separate, distinguishable ways.
Sex-linked genes are located on the sex chromosome
X^B or X^b or Y””
Describe the interactions between loci(epistasis)
In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus. One gene determines the pigment colour(for example) and the other gene determines whether the pigment will be deposited in the hair(for example).
Predict phenotypic ratios in problems involving epistasis
9(Dominant):3(Codominant):4(Recessive).
Describe the differences between continuous and discontinuous variation
Continuous: For any species, a characteristic that changes gradually over a range of values shows continuous variation.
Discontinuous: A characteristic of any species with only a limited number of possible values shows discontinuous variation.
Explain the basis of continuous and discontinuous variation by reference to the number of genes which influence the variation
Continuous: influenced by multiple genes. These genes have small effects of the phenotype. Traits that exhibit continuous variation, such as height or weight, often result from polygenic inheritance, where many genes have a combined effect.
Discontinuous: takes place only due to genetic factors. It means that the environment has no direct effect on discontinuous variation. At the genetic level, various genes have varying effects on the phenotype. Various alleles at a single gene locus have a huge effect on the phenotype.
Describe how both genotype and environment contribute to phenotypic variation
Phenotypic variability results from interactions between genotype and environment and is a major driver of ecological and evolutionary interactions.
Explain why variation is essential in selection
Genetic variation is essential for natural selection because natural selection can only increase of decrease frequency of alleles that already exist in the population. Survival of the fittest.
Last: Use the Hardy-Weinberg principle to calculate allele frequencies in populations
The frequency of dominant and recessive alleles will remain constant from generation to generation provided certain conditions exist. No selection is taking place and all alleles are equal; no mutation occurring; mating is random; population is large; no migration.
If you have two alleles for a single trait, the frequency of each one must add up to 1: p(dominant)+q(recessive)=1
p^2(homozygous dominant)+2pq(heterozygous)+q^2(homozygous recessive)=1.0.
Describe Darwin’s theory of evolution
In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification, but did not introduce his theory publicly. Natural selection is a process in which individuals with favorable inherited traits are more likely to survive and reproduce. In June 1858, Darwin received a manuscript from Alfred Russel Wallace, who had developed a theory of natural selection similar to Darwin’s. Darwin quickly finished The Origin of Species and published it the next year.
The unity of life, diversity of life, and the match between organisms and their environment.
Explain Darwin’s ideas in the context of Lamarck, Alfred Russel Wallace, Voyage of the Beagle, Lyell, geology and biogeoraphy
Lamarck: hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics. The mechanisms he proposed are unsupported by evidence. Some doubt about the permanence of species preceded Darwin’s ideas.
Alfred Russel Wallace: naturalist who worked mainly in the Amazon basin. Independently came up with the same ideas as Darwin. Great support of Darwin and they published work together.
Voyage of the Beagle: during his travels on the Beagle, Darwin collected specimens of South American plants and animals. He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions. He experienced an earthquake in Chile and observed the uplift of rocks.
Lyell: Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6,000 years old. His interest in geographic distribution of species was kindled by a stop at the Galapagos Islands west of South America. He hypothesized that species from South America had colonized the Galapagos and speciated on the islands.
Give examples to explain the principles of natural selection
Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals. Natural selection increases the match between organisms and their environment over time. If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species.
Note that individuals do not evolve; populations evolve over time. Natural selection can only increase or decrease heritable traits that vary in a population. Adaptations vary with different environments.
Explain, with examples, how evolution produces a tree-like relationship between organisms
As lineages evolve and split and modifications are inherited, their evolutionary paths diverge. This produces a branching pattern of evolutionary relationships. By studying inherited species’ characteristics and other historical evidence, we can reconstruct evolutionary relationships and represent them on a ‘family tree’ called a phylogeny.
