biology - cell and nuclear division + HL gene expression

Describe cell proliferation and its significance in multicellular organisms.

Cell proliferation is a rapid increase in the number of cells through mitosis, essential for growth, cell replacement, and tissue repair in multicellular organisms.

Explain the consequences of uncontrolled cell proliferation.

Uncontrolled cell proliferation can lead to cancer.

How does cell proliferation occur during embryonic development in animals?

During embryonic development, cell proliferation occurs throughout the animal embryo.

Define meristems in the context of plant cell proliferation.

Meristems are growth regions in plants where cell proliferation is confined, allowing for growth.

What are apical meristems and where are they located?

Apical meristems are found at the tips of stems and roots, responsible for producing new cells that elongate and extend the plant.

Describe the difference between shoot apical meristem and root apical meristem.

The shoot apical meristem is more complex than the root apical meristem, producing cells that elongate the shoot and form lateral organs like leaves and branches.

Explain the process of cell replacement in the epidermis.

Cell division occurs in the basal layer of the epidermis, where new cells are produced and displaced towards the skin surface, leading to the formation of keratin and eventual flaking off of dead cells.

How does tissue repair occur after a wound?

Tissue repair involves proliferation of stem cells in the dermis, which can repair damage unless the wounds are very thick.

What happens during the interphase of the cell cycle?

Interphase is an active phase of the cell cycle where many processes occur in the nucleus and cytoplasm.

Describe the growth phase (G1) of the cell cycle.

During the growth phase (G1), the cell increases in size and produces proteins and enzymes necessary for DNA replication.

What occurs during the S-phase of the cell cycle?

During the S-phase, DNA is duplicated to ensure each daughter cell receives one full set of chromosomes.

What is the significance of the G2 phase in the cell cycle?

The G2 phase is the period after DNA replication, where the cell prepares for mitosis.

Describe the role of cyclins in the cell cycle.

Cyclins are proteins responsible for the progression of the cell cycle. They become active when coupled with enzymes called cyclin-dependent kinases (CDKs), forming a complex that is phosphorylated to activate other proteins that advance the cell cycle.

Explain the difference between mitosis and meiosis.

Mitosis maintains the chromosome number and genome of cells, producing diploid cells, while meiosis halves the chromosome number, producing haploid cells for sex cell formation and generating genetic diversity.

Define cell division and its importance.

Cell division is the process by which a parent cell divides to produce two daughter cells. It is essential for growth, maintenance, and reproduction in organisms.

How does the parent cell behave during cell division?

The parent cell disappears as an entity during division, unlike in animal reproduction where parents remain separate from their offspring.

Explain the theory of Cell Continuity.

The theory of Cell Continuity states that all cells arise from pre-existing cells. This concept traces back to the zygote, which divides repeatedly to form a multicellular organism.

Describe the process of cytokinesis.

Cytokinesis is the process that divides the cytoplasm between daughter cells, completing cell division and ensuring each daughter cell has the necessary organelles and resources to function independently.

What is equal cytokinesis?

Equal cytokinesis is when the cytoplasm is divided evenly between daughter cells, which is common in most somatic (body) cells.

What is unequal cytokinesis?

Unequal cytokinesis is a process where the cytoplasm is not divided evenly between daughter cells, often resulting in one cell receiving more cytoplasm and organelles than the other.

Describe the process that occurs before a cell divides.

Before a cell divides, it must replicate its own DNA to ensure that each daughter cell receives a complete set of genetic instructions.

Explain the role of cohesin proteins during DNA replication.

Cohesin proteins hold sister chromatids together during DNA replication until they are separated during cell division.

Define the four stages of mitosis.

The four stages of mitosis are: 1. Prophase: chromosomes condense and become visible, 2. Metaphase: chromosomes align at the cell equator, 3. Anaphase: sister chromatids are pulled apart via microtubules, 4. Telophase: nuclear membranes reform around separated chromatids.

How does cytokinesis contribute to cell division?

Cytokinesis divides the cytoplasm equally between daughter cells, ensuring both cells receive the resources they need to survive and function.

What is the significance of symmetrical division in cytokinesis?

Symmetrical division in cytokinesis produces two daughter cells of similar size, allowing for equal distribution of resources.

Describe the organelle distribution during cytokinesis.

During cytokinesis, each daughter cell receives at least one mitochondrion and other essential organelles.

Explain the purpose of cell division in certain types of cells.

Cell division is common in cells that need to grow, repair tissues, or maintain genetic uniformity, such as skin cells or root tip cells in plants.

What happens during unequal cytokinesis?

Unequal cytokinesis produces daughter cells of different sizes, where one cell may retain most resources while the smaller cell may have a different function or may degenerate.

Why might one daughter cell be larger or better-resourced than the other?

One daughter cell may be specialized to retain most resources, such as nutrients and organelles, while the smaller cell may have a different function.

What is a requirement for both daughter cells regardless of cytokinesis type?

Regardless of whether cytokinesis is equal or unequal, both daughter cells must receive at least one of certain organelles that cannot be synthesized from scratch.

Why are mitochondria important for daughter cells?

Mitochondria cannot be made from scratch and must be inherited from the parent cell; each daughter cell must receive at least one mitochondrion to produce ATP.

What is the role of chloroplasts in plant cells during division?

Chloroplasts are essential organelles in plant cells, and like mitochondria, they must be inherited during cell division.

Describe oogenesis in humans.

Oogenesis is the production of egg cells (ova) in females, involving two rounds of unequal cytokinesis during meiosis.

Explain the first stage of oogenesis.

The first stage involves the formation of primary oocytes, which begins in the female fetus. Diploid germ cells (oogonia) undergo mitosis and enter meiosis I, becoming primary oocytes that are arrested in prophase I until puberty.

What occurs during the second stage of oogenesis after puberty?

During each menstrual cycle, one primary oocyte completes meiosis I, resulting in a secondary oocyte and a first polar body through unequal cytokinesis.

Define the outcome of the second stage of oogenesis.

The outcome is one secondary oocyte, which retains most of the cytoplasm, and a first polar body that eventually degenerates.

How does meiosis II contribute to oogenesis?

If fertilization occurs, the secondary oocyte completes meiosis II, resulting in a mature ovum and a second polar body through unequal cytokinesis.

Explain the final result of oogenesis.

The final result is one large, functional egg cell capable of supporting a developing embryo, and two or three small polar bodies that degenerate.

Describe the process of meiosis.

Meiosis involves DNA replication, separation of homologous chromosomes in meiosis I, and separation of sister chromatids in meiosis II, resulting in four genetically distinct haploid cells.

What is the significance of DNA replication in cell division?

DNA replication is essential for ensuring that each daughter cell receives an identical set of genetic instructions during cell division.

How does unequal cytokinesis affect the size of cells produced during oogenesis?

Unequal cytokinesis results in one large cell (the secondary oocyte or mature ovum) that retains most of the cytoplasm and smaller polar bodies that degenerate.

Explain the role of polar bodies in oogenesis.

Polar bodies are small cells produced during oogenesis that contain minimal cytoplasm and eventually degenerate, allowing the larger egg cell to retain resources for embryonic development.

Describe the process of chromosome movement during cell division.

The process involves three main stages: Attachment, Alignment, and Separation. In Attachment, microtubules from opposite poles attach to kinetochores on sister chromatids. During Alignment, motor proteins and microtubule dynamics position chromosomes at the cell's equator in metaphase. In Separation, during anaphase, cohesin proteins break down, and motor protein movement along with microtubule shortening pulls chromatids to opposite poles.

Explain the role of microtubules in mitosis.

Microtubules assemble into a mitotic spindle during prophase, guiding the chromosomes during division. They attach to kinetochores on the centromeres of each chromatid during metaphase, ensuring proper alignment and separation of chromosomes.

Define the stages of mitosis and their significance.

Mitosis consists of four stages: Prophase (chromatin condenses into visible chromosomes, and the nuclear envelope breaks down), Metaphase (chromosomes align at the metaphase plate), Anaphase (sister chromatids are pulled apart), and Telophase (nuclear envelopes reform and chromosomes decondense). Each stage is crucial for accurate chromosome segregation.

How do cohesin proteins function during anaphase?

Cohesin proteins hold sister chromatids together. During anaphase, these proteins are broken down, allowing spindle fibers to shorten and pull the sister chromatids apart toward opposite poles of the cell.

Explain the difference between cytokinesis in animal and plant cells.

In animal cells, cytokinesis involves the formation of a cleavage furrow that pinches the cell into two. In plant cells, a cell plate forms, which eventually develops into a new cell wall, separating the two daughter cells.

Describe the changes that occur during telophase.

During telophase, nuclear envelopes reform around the two sets of chromosomes at each pole, chromosomes decondense back into chromatin, spindle fibers disassemble, and the cell prepares for cytokinesis.

What is meiosis and its purpose?

Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and eggs) for sexual reproduction.

How does the alignment of chromosomes during metaphase ensure proper distribution to daughter cells?

During metaphase, chromosomes line up along the metaphase plate, and spindle fibers attach to kinetochores on the centromeres. This alignment ensures that each daughter cell receives one copy of each chromosome during separation.

What happens to the nuclear envelope during prophase?

During prophase, the nuclear envelope begins to break down, allowing chromosomes to move more freely in the cytoplasm.

Explain the significance of the mitotic spindle in cell division.

The mitotic spindle is crucial for the accurate segregation of chromosomes during cell division. It organizes and separates the chromosomes, ensuring that each daughter cell receives the correct number of chromosomes.

Describe the role of meiosis in preventing chromosome doubling.

Meiosis is essential to prevent chromosome doubling by producing haploid gametes, which ensure that fertilization restores the diploid number rather than doubling it each generation.

Explain how meiosis generates genetic variation.

Meiosis generates genetic variation through processes such as crossing over during Prophase 1 and independent assortment during Metaphase, creating unique combinations of alleles in each gamete.

Define non-disjunction and its consequences during meiosis.

Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis, which can lead to conditions like Down syndrome due to an abnormal number of chromosomes.

How does non-disjunction lead to Down syndrome?

Down syndrome is caused by trisomy 21, where an individual has three copies of chromosome 21 instead of the usual two, arising from non-disjunction during meiosis in one of the parent's gametes.

Identify factors that increase the likelihood of non-disjunction.

Factors that increase the likelihood of non-disjunction include maternal age (especially women over 35), environmental factors (such as exposure to chemicals or radiation), and cellular errors related to spindle fibers or cohesin proteins.

Describe the effects of non-disjunction on sex chromosomes.

Non-disjunction can affect sex chromosomes, leading to conditions such as Klinefelter Syndrome (XXY) with an extra sex chromosome, and Turner Syndrome (XO) with a missing sex chromosome.

Explain the process of crossing over during meiosis.

During prophase of meiosis, homologous chromosomes pair up to form bivalents, and non-sister chromatids exchange segments of DNA at points called chiasmata, resulting in genetic variation.

How does independent assortment contribute to genetic diversity?

Independent assortment during meiosis allows for the random orientation of bivalents, leading to the formation of gametes with different combinations of maternal and paternal chromosomes, thus contributing to genetic diversity.

What is the significance of genetic variation in evolution?

Genetic variation is the raw material for evolution and adaptation, allowing populations to adapt to changing environments and survive over generations.

Describe the cell cycle.

The cell cycle is a series of stages that a cell goes through to grow, replicate its DNA, and divide into two daughter cells.

Explain the two main stages of the cell cycle.

The two main stages of the cell cycle are Interphase, where the cell grows and prepares for division, and Mitosis, where the cell divides its nucleus and cytoplasm to form two identical daughter cells.

Define Interphase and its significance in the cell cycle.

Interphase is the stage of the cell cycle where the cell grows, performs its normal functions, and prepares for division, making it crucial for cell growth and DNA replication.

How is Interphase divided?

Interphase is divided into three stages: G1 phase, S phase, and G2 phase.

Describe the G1 phase of Interphase.

In the G1 phase, the cell increases in size, synthesizes essential proteins and organelles, and performs normal metabolic functions such as energy production and protein synthesis.

What occurs during the S phase of Interphase?

During the S phase, the cell duplicates its DNA so that each daughter cell will receive a complete set of genetic instructions, forming two identical sister chromatids.

Explain the G2 phase of Interphase.

In the G2 phase, the cell continues to grow, produce proteins, checks for errors in the replicated DNA, and assembles structures required for chromosome separation.

How does cell size and mass change during Interphase?

Cell size and mass double during Interphase, which depends on the biosynthesis of cell components like proteins and DNA, as well as the growth and division of mitochondria and chloroplasts.

What role do ribosomes play in the cell cycle?

Ribosomes produce proteins needed for growth, DNA replication, and cell division, including enzymes like DNA polymerase that facilitate DNA replication.

Describe the process of DNA replication during the S phase.

During the S phase, the cell duplicates its DNA, ensuring each daughter cell receives an identical copy, driven by enzymes like helicase and DNA polymerase.

What is the importance of DNA replication in the cell cycle?

DNA replication ensures genetic continuity, allowing each daughter cell to inherit the same genetic information as the parent cell.

Describe the role of mutations in proto-oncogenes and tumor suppressor genes in cancer development.

Mutations in proto-oncogenes and tumor suppressor genes disrupt the balance of the cell cycle, leading to excessive cell proliferation, loss of differentiation, and invasion and metastasis.

Explain excessive cell proliferation in the context of cancer.

Excessive cell proliferation occurs when cells divide rapidly, forming a mass known as a tumor.

Define loss of differentiation in tumor cells.

Loss of differentiation refers to tumor cells often losing their specialized functions, which is a characteristic of cancer.

How do malignant tumors affect other tissues in the body?

Malignant tumors can invade and metastasize, spreading to other tissues and causing cancer.

What is the relationship between the cell cycle and cancer?

The balance of the cell cycle is disrupted by mutations in proto-oncogenes and tumor suppressor genes, leading to cancerous growth.

Describe the consequences of tumor cell behavior on the body.

Tumor cells can lead to excessive proliferation, loss of specialized functions, and the ability to invade and metastasize to other tissues.

Describe gene expression and its significance in determining phenotype.

Gene expression is the process that determines how genes affect the phenotype of an organism. It bridges the genetic code (genotype) and observable traits (phenotype), which result from the interaction between genetic makeup and the environment.

Explain the relationship between genotype, environment, and phenotype.

The phenotype of an organism is the result of the interaction between its genotype (genetic makeup) and the environment. This relationship can be summarized by the equation: Phenotype = Genotype + Environment.

Define the three key stages of gene expression.

The three key stages of gene expression are transcription, translation, and protein function.

How does transcription occur in gene expression?

Transcription occurs in the nucleus and involves three sub-stages: Initiation (RNA polymerase binds to the promoter), Elongation (RNA polymerase synthesizes a complementary RNA strand), and Termination (transcription ends at a termination sequence, and mRNA undergoes processing).

What happens during the initiation stage of transcription?

During the initiation stage of transcription, the enzyme RNA polymerase binds to a specific region of DNA called the promoter, which acts as a start signal for transcription.

Describe the elongation stage of transcription.

In the elongation stage of transcription, RNA polymerase unwinds the DNA and synthesizes a complementary RNA strand using one strand of DNA as a template, growing the RNA strand in the 5 to 3 direction.

Explain the termination stage of transcription.

The termination stage of transcription occurs when RNA polymerase reaches a termination sequence on the DNA, leading to the detachment of the newly synthesized mRNA, which then undergoes processing.

What processing occurs to mRNA after transcription?

After transcription, mRNA undergoes processing where a cap and a poly-A tail are added for protection and transport, and non-coding regions (introns) are removed through splicing, leaving only coding regions (exons).

Define the process of translation in gene expression.

Translation is the process that occurs in the cytoplasm on ribosomes, where the mRNA sequence is decoded to produce a polypeptide chain, which is a sequence of amino acids.

What is the role of ribosomes during translation?

Ribosomes play a crucial role during translation by binding to the start codon on the mRNA and facilitating the decoding of the mRNA sequence to produce a polypeptide chain.

Describe the initiation stage of translation.

In the initiation stage of translation, the ribosome binds to the start codon (AUG) on the mRNA, which codes for the amino acid methionine, and transfer RNA (tRNA) molecules carry amino acids to the ribosome.

Describe the role of different cells in an organism despite having the same genome.

Different cells express different genes, leading to the production of specific proteins; for example, muscle cells produce muscle proteins while nerve cells produce neurotransmitters.

Explain how transcription is regulated in cells.

Transcription is regulated by controlling which genes are transcribed into mRNA, with proteins binding to specific DNA sequences to turn genes on or off.

Define a promoter in the context of gene transcription.

A promoter is a specific DNA sequence located near the start of a gene that acts as a binding site for RNA polymerase and other proteins needed to initiate transcription.

How does RNA polymerase initiate transcription at a promoter?

RNA polymerase binds to the promoter to start transcribing the gene, marking where transcription begins.

What is the significance of the TATA box in eukaryotic promoters?

The TATA box (TATAAA) is a common promoter sequence in eukaryotes that helps position RNA polymerase accurately for transcription.

Describe the function of enhancers in gene transcription.

Enhancers are DNA sequences that increase the rate of transcription when activator proteins bind to them, often located far from the gene they regulate.

Explain how enhancers increase transcription activity.

Enhancers work by DNA looping, bringing activator proteins bound to the enhancer close to the promoter, which increases RNA polymerase activity and boosts transcription.

Define silencers and their role in transcription.

Silencers are DNA sequences that decrease the rate of transcription when repressor proteins bind to them, reducing or blocking transcription.

How do repressor proteins affect transcription at silencers?

Repressor proteins bind to silencers and prevent RNA polymerase from effectively transcribing the gene.

What are transcription factors and their function in gene expression?

Transcription factors are proteins that control transcription by binding to specific DNA sequences, with activators increasing transcription rates.

Describe the role of activators in transcription regulation.

Activators bind to enhancers and increase the rate of transcription by assisting RNA polymerase in the transcription process.