D2 Continuity and Change: Molecules

D2.1 Cell and nuclear devision, D2.2 Gene Expression (HL), D2.3 Water Potential

Define genotype and phenotype.

Genotype is the genetic makeup of an organism, while phenotype is the observable physical or biochemical characteristics determined by the genotype and environment.

Define gene expression.

Gene expression is the process by which the information in a gene is used to synthesize a functional gene product, such as a protein or RNA.

List the most common stages in the process of gene expression.

The most common stages are transcription, RNA processing, translation, and post-translational modification.

Explain the regulation of transcription by a transcription factor binding to the promoter sequence of DNA.

Transcription factors bind to promoter sequences to recruit or block RNA polymerase, thereby enhancing or repressing the transcription of a gene.

Compare the function of enhancer and silencer DNA sequences.

Enhancers increase the rate of transcription by binding activator proteins, while silencers decrease transcription by binding repressor proteins.

Compare the function of repressor and activator transcription factors.

Repressors inhibit transcription by blocking RNA polymerase or preventing activator binding, while activators promote transcription by helping recruit RNA polymerase to the promoter.

Outline how the length of the poly

A tail on mRNA impacts degradation of mRNA by nucleases. - A longer poly-A tail stabilizes the mRNA and delays degradation; a shorter tail leads to faster degradation by nucleases.

Outline how the degradation of mRNA is a mechanism of regulating translation.

By controlling how long mRNA remains intact in the cytoplasm, cells can regulate how much protein is translated from that mRNA.

Define epigenesis and epigenome.

Epigenesis is the development of differentiated cell types in multicellular organisms. The epigenome refers to chemical modifications to DNA and histones that affect gene expression without altering the DNA sequence.

Compare the genome, transcriptome and proteome.

The genome is the complete DNA sequence of an organism, the transcriptome is the full set of RNA transcripts, and the proteome is the complete set of proteins expressed by a cell or organism.

Describe the impact of methylation of DNA in the promoter of DNA on gene expression.

Methylation of promoter DNA usually represses gene expression by preventing transcription factor binding.

Describe the impact of acetylation and methylation of histone proteins on gene expression.

Acetylation of histones loosens DNA-histone interactions, promoting transcription, while methylation can either activate or repress gene expression depending on the site.

Describe the inheritance of epigenetic tags in differentiated cells of a multicellular organism.

Epigenetic tags such as DNA methylation and histone modification are maintained through cell divisions, preserving gene expression patterns in differentiated cells.

Discuss the consequences of reprogramming and imprinting of epigenetic tags in haploid gametes.

Reprogramming removes most epigenetic marks to reset gene expression, but some imprinted genes retain tags to ensure parent-specific expression in the offspring.

Outline the impact of air pollution on the epigenetic regulation of genes associated with the immune response.

Air pollution can lead to DNA methylation changes that suppress or alter the expression of immune response genes, increasing susceptibility to diseases.

Discuss how imprinting of epigenetic tags impacts gene expression in a diploid cell.

Imprinting causes one allele of a gene (either maternal or paternal) to be epigenetically silenced, so only one functional copy is expressed in diploid cells.

Outline the epigenetic origins in the difference in size between tigons and ligers (lion-tiger hybrids).

Due to parent-specific imprinting, genes promoting growth from the father are overexpressed in ligers (male lion × female tiger) and underexpressed in tigons (male tiger × female lion), causing size differences.

Explain the reason why monozygotic twin studies are often used to measure the impact of the environment on gene expression.

Monozygotic twins have identical DNA, so differences in gene expression between them are due to environmental and epigenetic factors, not genetic variation.

Outline the mechanism by which the presence of lactose regulates the expression of genes related to digestion and use of lactose in E. coli.

Lactose binds to the lac repressor, causing it to release from the operator, allowing RNA polymerase to transcribe genes for lactose metabolism.

Outline the mechanism by which the presence of oestrogen in a cell's environment regulates the expression of genes related to endometrium development and maintenance during the uterine cycle.

Oestrogen binds to intracellular receptors that act as transcription factors, activating genes necessary for endometrial development and maintenance.

List implications of the idea that new cells are only produced from a pre

existing cell. - All cells trace their origin to existing cells, ensuring genetic continuity, limiting the possibility of spontaneous cell generation, and supporting the cell theory.

Define cytokinesis.

Cytokinesis is the division of the cytoplasm to form two separate daughter cells after mitosis or meiosis.

State the difference between mitosis and cytokinesis.

Mitosis is the division of the nucleus, while cytokinesis is the division of the cytoplasm.

Compare and contrast cytokinesis in plant and animal cells.

In animal cells, a cleavage furrow forms to divide the cell. In plant cells, a cell plate forms which becomes the new cell wall.

Describe the formation of the cleavage furrow in animal cell cytokinesis.

Microfilaments (actin and myosin) contract at the cell's equator, pinching the membrane to form a cleavage furrow that deepens until the cell splits.

Describe the formation of the cell wall in plant cell cytokinesis.

Vesicles from the Golgi apparatus coalesce at the center to form a cell plate, which develops into a new cell wall separating the two daughter cells.

State that cytokinesis usually, but not always, results in equal division of the cytoplasm.

Cytokinesis usually results in equal cytoplasmic division, but exceptions occur in processes like budding or oogenesis.

State the reason why daughter cells must receive at least one mitochondria during cytokinesis.

Mitochondria are needed for ATP production; without them, cells can't carry out energy-requiring processes.

Outline unequal cytokinesis in yeast budding.

A small daughter cell forms and buds off from the larger parent cell, receiving less cytoplasm but sufficient organelles.

Outline unequal cytokinesis during human oogenesis.

Oogenesis produces one large ovum and smaller polar bodies by unequal division of the cytoplasm during meiosis.

State that mitosis is nuclear division resulting in continuity of the chromosome number and genome.

Mitosis ensures each daughter cell receives an identical set of chromosomes, maintaining genome continuity.

State that meiosis is nuclear division that results in reduction of the chromosome number and diversity between genomes.

Meiosis reduces the chromosome number by half and increases genetic variation through recombination.

Outline the cause and consequence of anucleate cells.

Anucleate cells result from improper cell division; they lack a nucleus and cannot divide or transcribe DNA.

State that DNA replication occurs before both mitosis and meiosis.

DNA replication occurs before both types of cell division to ensure each daughter cell receives a full set of genetic material.

State that DNA replication occurs in S

phase of interphase. - DNA replication takes place during the S-phase of interphase, before mitosis or meiosis begins.

Explain how replicated DNA molecules are held together, with reference to chromatid, replicated chromosome, centromere and cohesin.

Sister chromatids are joined at the centromere by cohesin proteins, forming a replicated chromosome.

Explain how and why chromosomes condense during mitosis and meiosis.

Chromosomes condense via supercoiling to become more compact and prevent damage or tangling during division.

State the role of microtubules and kinetochore motor proteins.

Microtubules form the spindle, and motor proteins at kinetochores move chromosomes during cell division.

State the names of the four phases of mitosis.

Prophase, Metaphase, Anaphase, Telophase.

Draw typical eukaryotic cells as they would appear during the interphase and the four phases of mitosis.

[Diagram required]

Outline four events that occur during prophase.

Chromosomes condense, nuclear envelope breaks down, spindle forms, centrioles move to poles.

Outline the process of metaphase, inclusive of the role of microtubules and the kinetochore.

Chromosomes align at the equator; spindle microtubules attach to kinetochores at centromeres.

Outline the process of anaphase.

Sister chromatids are pulled apart by spindle fibers to opposite poles of the cell.

Outline four events that occur during telophase.

Chromosomes decondense, nuclear envelopes reform, spindle breaks down, nucleoli reappear.

Determine the phase of mitosis of a cell viewed in a diagram, micrograph or with a microscope.

Identify based on chromosome alignment, presence of spindle, nuclear envelope status, and chromatid separation.

Explain what it means for chromosomes to be "homologous."

Homologous chromosomes are pairs with the same genes at the same loci but may carry different alleles.

Define diploid.

A diploid cell has two complete sets of chromosomes (2n).

State the human cell diploid number.

46 chromosomes.

Define haploid.

A haploid cell has one complete set of chromosomes (n).

State the human cell haploid number.

23 chromosomes.

List example haploid cells.

Sperm, egg (gametes).

Given a diploid number (for example 2n=4), outline the movement and structure of DNA through the stages of meiosis.

DNA replicates (4 chromosomes, 8 chromatids), homologs separate in meiosis I, sister chromatids separate in meiosis II, producing four haploid cells.

Explain why meiosis I is a reductive division.

It halves the chromosome number by separating homologous chromosomes.

State that cells are haploid at the end of meiosis I.

Cells have one set of chromosomes (n) after meiosis I.

Compare meiosis with mitosis.

Meiosis produces 4 genetically different haploid cells; mitosis produces 2 identical diploid cells.

Outline the events of prophase, metaphase, anaphase and telophase in meiosis I and meiosis II.

Meiosis I: homologs pair, align, separate. Meiosis II: chromatids align, separate like mitosis. Telophase events mirror mitotic telophase.

Define nondisjunction.

Failure of chromosomes or chromatids to separate properly during meiosis.

State the result of nondisjunction during anaphase I and anaphase II.

Anaphase I: all gametes affected. Anaphase II: half of the gametes affected.

Describe the cause and symptoms of Down syndrome.

Caused by trisomy 21 due to nondisjunction; symptoms include intellectual disability, distinct facial features, heart defects.

Explain how meiosis leads to genetic variation in gametes.

Through crossing over, random orientation, and independent assortment of chromosomes.

Define bivalent.

A pair of homologous chromosomes aligned during meiosis I.

Describe the process and result of crossing over during prophase I of meiosis.

Homologous chromosomes exchange genetic material, creating recombinant chromatids.

Draw a diagram to illustrate the formation of new allele combinations as a result of crossing over.

[Diagram required]

Describe the process and result of random orientation of bivalents during metaphase I of meiosis.

Homologs align randomly at the metaphase plate, increasing genetic variation.

Draw a diagram to illustrate the formation of different chromosome combinations that result from random orientation during meiosis.

[Diagram required]

State that the number of chromosome combinations possible due to random orientation is 2^n.

2^n, where n is the haploid number.

Define cell proliferation.

The increase in cell number by repeated cell division.

List three processes which require cell proliferation.

Growth, tissue repair, development.

Outline cell proliferation during growth at plant meristems and early

stage animal embryos. - Meristematic and embryonic cells rapidly divide to form tissues and organs.

Describe skin cell proliferation during cell replacement and tissue repair.

Basal cells divide to replace dead or damaged cells.

List the phases of the cell cycle.

G1, S, G2, M (mitosis), and cytokinesis.

Distinguish between interphase, mitosis and cytokinesis.

Interphase: cell growth and DNA replication. Mitosis: nuclear division. Cytokinesis: cytoplasmic division.

Outline events of the G1, S, and G2 phases of interphase.

G1: growth, protein synthesis. S: DNA replication. G2: preparation for mitosis.

Outline the fate of cells that leave the cell cycle.

They enter G0, becoming quiescent or specialized, and may not divide again.

Outline the structures that must be produced by a cell as it grows prior to division.

Organelles, proteins, enzymes, DNA, membranes.

List example metabolic reactions occurring during cell interphase.

Protein synthesis, DNA replication, ATP production, lipid synthesis.

State the functions of cell cycle checkpoints.

Ensure accurate DNA replication and division; prevent progression with errors.

Outline events of the G1, G2 and M checkpoints.

G1: checks size and DNA damage. G2: checks replication completeness. M: checks spindle attachment.

Outline the role of cyclins in controlling the cell cycle.

Cyclins activate cyclin-dependent kinases to regulate progression through the cell cycle.

Interpret a graph of cyclin concentrations throughout the cell cycle.

Cyclin levels rise and fall in a predictable pattern to control specific checkpoints.

Describe how cancer arises, referring to accumulation of mutations over time.

Mutations in genes regulating division lead to uncontrolled proliferation and tumor formation.

Define and list mutagens.

Agents causing DNA mutations, e.g., UV radiation, chemicals, viruses.

Explain how mutations to proto

oncogenes and tumor suppressor genes can lead to the development of cancer. - Proto-oncogene activation and tumor suppressor inactivation lead to loss of cell cycle control.

Compare the rates of cell division and growth and the capacity for metastasis and invasion of neighboring tissues between normal cells and cancerous cells.

Cancer cells divide faster, grow uncontrollably, and can invade tissues and metastasize.

Define primary tumor, secondary tumor, benign, malignant, metastasis and cancer.

Primary tumor: original tumor. Secondary: spread tumor. Benign: non-invasive. Malignant: invasive. Metastasis: spread of cancer. Cancer: disease of uncontrolled cell growth.

State the formula for calculation of a mitotic index.

Mitotic index = (number of cells in mitosis / total number of cells) × 100.

Calculate the mitotic index of a tissue as seen in a micrograph.

Count cells in mitosis and total cells, apply the formula.

Outline the use of mitotic index calculations in diagnosis and treatment of cancer.

High mitotic index indicates active cell division, used in cancer diagnosis, grading, and monitoring treatment response.

Identify solvent and solutes of a solution.

The solvent is the substance in which the solutes dissolve, typically present in greater quantity; the solutes are the substances that are dissolved in the solvent.

Define solvation.

Solvation is the process of surrounding solute particles with solvent molecules to form a solution.

Explain why water is able to dissolve charged and polar molecules.

Water is a polar molecule with partial positive and negative charges, allowing it to form electrostatic interactions and hydrogen bonds with charged and polar solutes, thus dissolving them.

Outline the solvation of hydrophilic and hydrophobic substances.

Hydrophilic substances dissolve in water as they form hydrogen bonds or ionic interactions with water molecules; hydrophobic substances do not dissolve in water and aggregate together to minimize contact with water.

Define osmolarity, isotonic, hypotonic and hypertonic.

Osmolarity is the concentration of solute particles in a solution; isotonic solutions have equal osmolarity to the cell; hypotonic solutions have lower osmolarity than the cell; hypertonic solutions have higher osmolarity than the cell.

State the unit for concentration of a solute in a volume of solution.

The unit is moles per liter (mol/L or M).

Outline the net movement of water between hypotonic, hypertonic and isotonic solutions.

Water moves from hypotonic (lower solute concentration) to hypertonic (higher solute concentration) solutions; there is no net movement of water between isotonic solutions.

Compare the relative permeability of the plasma membrane to water and solutes.

The plasma membrane is more permeable to water (via aquaporins) than to solutes, which often require specific transport proteins.

Define osmosis.

Osmosis is the passive movement of water across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration.

State that osmosis is a form of passive transport.

Osmosis is a form of passive transport because it does not require energy input.

Explain what happens to cells when placed in isotonic, hypotonic and hypertonic solutions.

In isotonic solutions, cells retain shape; in hypotonic solutions, cells swell (and may burst without a cell wall); in hypertonic solutions, cells shrink (crenate or plasmolyze).

Explain the change in mass and/or volume of plant tissues placed in either hypotonic or hypertonic solutions.

In hypotonic solutions, plant tissues gain mass and volume as water enters; in hypertonic solutions, they lose mass and volume due to water loss.