What is the structure and function of the nucleus?
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The nucleus is a spherical or oval-shaped structure that is usually the most prominent feature of a cell. It is separated from the cytoplasm by a double membrane called the nuclear envelope, which has nuclear pores that control the movement of substances between the nucleus and the cytoplasm. Inside the nucleus are nucleoli, which produce ribosomes, and chromatin, which contains the cell's hereditary units called genes.
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What is the structure and function of the nucleus?
The nucleus is a spherical or oval-shaped structure that is usually the most prominent feature of a cell. It is separated from the cytoplasm by a double membrane called the nuclear envelope, which has nuclear pores that control the movement of substances between the nucleus and the cytoplasm. Inside the nucleus are nucleoli, which produce ribosomes, and chromatin, which contains the cell's hereditary units called genes.
What forms when the large and small ribosomal subunits join together?
A functional ribosome
What is Tay-Sachs disease and what causes it?
Tay-Sachs disease is an inherited condition caused by the absence of the lysosomal enzyme Hex A, leading to the accumulation of ganglioside GM2 in nerve cells.
What are the four stages of mitosis?
Prophase, metaphase, anaphase, and telophase.
Why must DNA replication occur before cytokinesis in somatic cell division?
DNA replication must occur before cytokinesis to ensure that each daughter cell receives an identical set of chromosomes.
What pairs with the next mRNA codon at the A site?
Anticodon of incoming tRNA
Where are mitochondria usually located within the cell?
Mitochondria are usually located where oxygen enters the cell or where ATP is used, such as among the contractile proteins in muscle cells.
What is a chromosome?
A highly coiled and folded DNA molecule combined with protein molecules.
What is the cytoskeleton composed of?
Three protein filaments: microfilaments, intermediate filaments, and microtubules.
What are the functions of rough ER?
Synthesizes glycoproteins and phospholipids that are transferred to cellular organelles, inserted into the plasma membrane, or secreted during exocytosis.
What are cyclin-dependent protein kinases (Cdk's) responsible for?
Transferring a phosphate group from ATP to a protein to activate it, and their activation and deactivation are crucial in the initiation and regulation of DNA replication, mitosis, and cytokinesis.
What is the role of mitochondria?
Mitochondria are the site of aerobic cellular respiration reactions that produce most of a cell’s ATP and play an important early role in apoptosis.
When does cytokinesis begin?
Cytokinesis begins during anaphase and is completed after telophase.
During which phase of the cell cycle does DNA replication occur?
S phase
What happens to the ribosomal subunits when protein synthesis is complete?
They separate
What are some disorders with significant genetic components that genomic medicine aims to address?
Genomic medicine aims to address disorders such as hypertension, obesity, diabetes, and cancer.
Where does RNA polymerase attach to the DNA to begin transcription?
RNA polymerase attaches to the DNA at a special nucleotide sequence called a promoter, which is located near the beginning of a gene.
What occurs during translation?
During translation, the RNA attaches to a ribosome, where the information contained in RNA is translated into a corresponding sequence of amino acids to form a new protein molecule.
What are diploid cells?
Diploid cells are somatic cells that contain two sets of chromosomes.
What is apoptosis?
An orderly, genetically programmed cell death where the cell shrinks and pulls away from neighboring cells.
What occurs during prophase of mitosis?
Chromatin fibers condense into paired chromatids, the nucleolus and nuclear envelope disappear, and each centrosome moves to an opposite pole of the cell.
What is the function of proteasomes?
Proteasomes are responsible for the continuous destruction of unneeded, damaged, or faulty proteins.
What is chromatin?
Chromatin is a complex of DNA, proteins, and some RNA found within the nucleus. It appears as a diffuse, granular mass in cells that are not dividing and has a beads-on-a-string structure.
What happens to the tRNA previously at the P site after the ribosome shifts by one codon?
It enters the E site and is released from the ribosome
How is DNA packed in the nucleus?
DNA is packed in the nucleus by coiling around histones to form nucleosomes, which further coil into chromatin fibers and eventually condense into chromatids before cell division.
What occurs during transcription in the nucleus?
During transcription, the genetic information represented by the sequence of base triplets in DNA serves as a template for copying the information into a complementary sequence of codons.
Where does transcription occur and what is its purpose?
Transcription occurs in the nucleus and its purpose is to copy the genetic information in DNA to RNA.
What are the functions of smooth ER?
Synthesizes fatty acids and steroids, inactivates or detoxifies drugs, removes phosphate group from glucose-6-phosphate, and stores and releases calcium ions in muscle cells.
What occurs during the G1 phase?
During the G1 phase, the cell is metabolically active, replicates most of its organelles and cytosolic components, and begins replication of centrosomes.
What is the metaphase plate?
The plane of alignment of the centromeres of chromatid pairs at the center of the mitotic spindle during metaphase.
What happens during the G1 phase of interphase?
The cell is metabolically active, duplicates most of its organelles and cytosolic components, and begins replication of chromosomes.
When does protein synthesis end?
Protein synthesis ends when the ribosome reaches a stop codon at the A site, causing the completed protein to detach from the final tRNA.
What is the role of the E site in a ribosome?
The E (exit) site binds tRNA just before it is released from the ribosome.
What are the functions of lysosomes?
Lysosomes digest substances that enter a cell via endocytosis, carry out autophagy, implement autolysis, and accomplish extracellular digestion.
What is the function of the mitotic spindle?
The mitotic spindle is responsible for separating the chromosomes during mitosis.
How does regular exercise affect the number of mitochondria in muscle cells?
Regular exercise can lead to an increase in the number of mitochondria in muscle cells, allowing them to function more efficiently.
What role do mitochondria play in apoptosis?
Mitochondria play an important early role in apoptosis.
What is the function of the plasma membrane?
Protects cellular contents, makes contact with other cells, contains channels, transporters, receptors, enzymes, cell-identity markers, and linker proteins; mediates entry and exit of substances.
What enzyme catalyzes the transcription of DNA?
The enzyme RNA polymerase catalyzes the transcription of DNA.
What happens during transcription?
During transcription, the information encoded in a specific region of DNA is transcribed (copied) to produce a specific molecule of RNA.
What maintains homeostasis in cell destiny?
A balance between cell proliferation and cell death.
What is the function of proteasomes?
Proteasomes degrade unneeded, damaged, or faulty proteins by cutting them into small peptides.
What is reproductive cell division?
Reproductive cell division is the mechanism that produces gametes through a special two-step division called meiosis.
What is the mitotic phase?
The phase where the parent cell produces identical cells with identical chromosomes, and chromosomes are visible under a light microscope.
What occurs at the A site of the ribosome during translation?
The anticodon of another tRNA with its attached amino acid pairs with the second mRNA codon at the A site.
What are nucleoli and their function?
Nucleoli are spherical bodies within the nucleus that function in producing ribosomes. They are sites of synthesis of rRNA and assembly of rRNA and proteins into ribosomal subunits.
What is the role of the kinetochore during mitosis?
The kinetochore is a protein complex that attaches to microtubules of the mitotic spindle.
What are mitochondrial cristae?
Mitochondrial cristae are a series of folds in the internal mitochondrial membrane.
What is the role of transfer RNA (tRNA) during translation?
Transfer RNA (tRNA) binds to an amino acid and holds it in place on a ribosome until it is incorporated into a protein during translation. One end of the tRNA carries a specific amino acid, and the opposite end consists of a triplet of nucleotides called an anticodon.
What is the centrosome composed of?
A pair of centrioles plus pericentriolar matrix.
What is the cell cycle?
The cell cycle is an orderly sequence of events in which a somatic cell duplicates its contents and divides in two.
What role do cyclins play in the cell cycle?
Cyclins switch Cdk's on and off, triggering various events that control cell division.
What happens during the G2 phase?
During the G2 phase, cell growth continues, enzymes and other proteins are synthesized in preparation for cell division, and replication of centrosomes is completed.
What occurs during the S phase of interphase?
Replication of DNA and centrosomes.
What is a polyribosome?
Several ribosomes attached to the same mRNA, allowing the translation of one mRNA into several identical proteins simultaneously.
What is the function of the initiator tRNA during translation?
The initiator tRNA binds to the start codon (AUG) on mRNA, where translation begins, and carries the amino acid methionine.
What are some side effects of anticancer drugs that inhibit the mitotic spindle?
Side effects include nausea, diarrhea, hair loss, fatigue, and decreased resistance to disease.
What is the nuclear envelope and its function?
The nuclear envelope is a double membrane that separates the nucleus from the cytoplasm. It has nuclear pores that control the movement of substances between the nucleus and the cytoplasm.
What is a nucleosome?
A nucleosome is a bead-like structure in chromatin, consisting of double-stranded DNA wrapped twice around a core of eight proteins called histones.
How do large particles enter and exit the nucleus?
Large particles enter and exit the nucleus through nuclear pores.
How many genes are in the human genome?
The human genome contains about 30,000 genes.
What is the function of cytosol?
Fluid in which many of the cell’s metabolic reactions occur.
What is the endoplasmic reticulum (ER) and its types?
A membranous network of flattened sacs or tubules; Rough ER is covered by ribosomes and attached to the nuclear envelope; Smooth ER lacks ribosomes.
What are the functions of the Golgi complex?
The Golgi complex accepts proteins from the rough ER, forms glycoproteins, glycolipids, and lipoproteins, and sorts and packages molecules for transport to their destinations.
What are the three phases of interphase?
The three phases of interphase are G1, S, and G2.
How is a peptide bond formed during translation?
A component of the large ribosomal subunit catalyzes the formation of a peptide bond between methionine and the amino acid carried by the tRNA at the A site.
What is alternative splicing?
Alternative splicing is a process where pre-mRNA is spliced in different ways to produce several different mRNAs, which are then translated into different proteins.
What is a neoplasm or tumor?
A neoplasm or tumor is a mass of cells resulting from uncontrolled cell division.
How do some anticancer drugs work?
Some anticancer drugs work by inhibiting the formation of the mitotic spindle, thereby stopping cell division.
How can new peroxisomes form?
New peroxisomes can form by enlarging and dividing from preexisting ones or by accumulating components at a site in the cell and assembling.
What are genes and where are they located?
Genes are the cell's hereditary units that control cellular structure and direct cellular activities. They are located within the nucleus, arranged along chromosomes.
Where does the initiator tRNA fit into the ribosome?
P site
What forms a peptide bond with the amino acid at the A site?
Amino acid on tRNA at P site
What is the focus of genomics?
Genomics focuses on the study of the relationships between the genome and the biological functions of an organism.
What is the function of cilia and flagella?
Cilia move fluids over the cell’s surface; flagella move the entire cell.
What are the three possible destinies of a cell?
To remain alive and functioning without dividing, to grow and divide, or to die.
What happens during interphase?
During interphase, the cell replicates its DNA, produces additional organelles and cytosolic components, and undergoes high metabolic activity.
What happens during anaphase of mitosis?
The centromeres split, separating the chromatids, which move toward opposite poles of the cell and are then termed chromosomes.
What are introns and exons?
Introns are regions within a gene that do not code for parts of proteins, while exons are regions that do code for segments of a protein.
What happens to chromatin fibers during early prophase?
Chromatin fibers condense and shorten into visible chromosomes.
Where are ribosomes produced?
Ribosomes are produced in the nucleoli.
What forms a pair of chromatids?
Two identical DNA molecules and their histones, held together by a centromere.
What is the function of the cytoskeleton?
Maintains shape and general organization of cellular contents; responsible for cell movements.
What is a base triplet in DNA?
A base triplet is a sequence of three nucleotides in DNA.
What are the two major periods of the cell cycle?
The two major periods of the cell cycle are interphase and the mitotic (M) phase.
What are the functions of nuclear pores?
Nuclear pores control the movement of substances between the nucleus and cytoplasm.
What are some therapeutic substances produced by recombinant bacteria?
Recombinant bacteria produce substances such as human growth hormone (hGH), insulin, interferon (IFN), and erythropoietin (EPO).
What is the role of the A site in a ribosome?
The A (aminoacyl) site binds the tRNA carrying the next amino acid to be added to the growing polypeptide.
What is the role of peroxisomes in protecting the cell?
Peroxisomes protect the cell by containing enzymes that decompose hydrogen peroxide and destroy superoxide, preventing toxic effects.
What holds the chromatid pair together during prophase?
A centromere holds the chromatid pair together.
What is the result of the mitotic (M) phase of the cell cycle?
The formation of two identical cells through nuclear division (mitosis) and cytoplasmic division (cytokinesis).
What is the function of proteasomes in the cell?
Proteasomes degrade proteins into small peptides and amino acids, which can be recycled into new proteins.
What are the components of a nucleosome?
Histones (proteins) and DNA.
What is the cytoplasm?
Cellular contents between plasma membrane and nucleus, including cytosol and organelles.
If the DNA template had the base sequence AGCT, what would be the mRNA base sequence, and what enzyme would catalyze DNA transcription?
The mRNA base sequence would be UCGA, and the enzyme that catalyzes DNA transcription is RNA polymerase.
How many pairs of chromosomes do human cells contain?
Human cells contain 23 pairs of chromosomes, for a total of 46.
What is somatic cell division?
Somatic cell division is the process by which a somatic cell undergoes mitosis and cytokinesis to produce two genetically identical cells.
What happens during the G2 phase of interphase?
Cell growth, enzyme and protein synthesis continue, and replication of centrosomes is completed.
What are nuclear pores and their function?
Nuclear pores are openings in the nuclear envelope that control the movement of substances between the nucleus and the cytoplasm. Small molecules and ions move through the pores passively by diffusion, while large molecules like RNAs and proteins are transported actively.
What is the genome?
The genome is the total genetic information carried in a cell or an organism.
What are the two membranes of a mitochondrion called?
The external mitochondrial membrane and the internal mitochondrial membrane.
What are the complementary base pairings during transcription?
During transcription, the bases cytosine (C), guanine (G), and thymine (T) in the DNA template pair with guanine (G), cytosine (C), and adenine (A), respectively, in the RNA strand.
What is meiosis?
Meiosis is a type of cell division in which the number of chromosomes in the nucleus is reduced by half.
What are the functions of lysosomes?
Lysosomes fuse with and digest contents of endosomes, phagosomes, and vesicles, transport final products of digestion into the cytosol, and digest worn-out organelles, entire cells, and extracellular materials.
What forms the cleavage furrow during cytokinesis?
Actin microfilaments form a contractile ring that pulls the plasma membrane inward, constricting the cell and ultimately pinching it in two.
What happens to the tRNA in the P site after the ribosome shifts the mRNA strand by one codon?
The tRNA in the P site enters the E site and is subsequently released from the ribosome.
What enzyme do peroxisomes contain to decompose hydrogen peroxide?
Peroxisomes contain the enzyme catalase to decompose hydrogen peroxide.
What attaches to a start codon during the initiation of protein synthesis?
Initiator tRNA
What happens to the tRNA previously at the A site after the ribosome shifts by one codon?
It is now at the P site
What is chromatin?
Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.
What is the proteome?
The proteome refers to all of an organism’s proteins.
What is a codon?
A codon is a complementary sequence of three nucleotides transcribed from a DNA base triplet.
What do peroxisomes do?
Peroxisomes oxidize amino acids and fatty acids and detoxify harmful substances such as hydrogen peroxide and associated free radicals.
What is the function of nucleoli?
Nucleoli produce ribosomes.
What is the role of the terminator in transcription?
The terminator specifies the end of the gene, causing RNA polymerase to detach from the transcribed RNA molecule and the DNA strand.
Why are mitochondria referred to as the 'powerhouses' of the cell?
Because they generate most of the ATP through aerobic (oxygen-requiring) respiration.
What diseases are associated with the failure of proteasomes to degrade abnormal proteins?
Parkinson’s disease and Alzheimer’s disease.
What is gene expression?
Gene expression is the process where a gene’s DNA is used as a template for the synthesis of a specific protein.
What is the genetic code?
The genetic code is the set of rules that relate the base triplet sequence of DNA to the corresponding codons of RNA and the amino acids they specify.
What happens to cyclin levels during the cell cycle?
Cyclin levels rise and fall, determining the timing and sequence of events in cell division.
What do chromosomes consist of?
Chromosomes consist of genes that control cellular structure and direct cellular functions.
When does protein synthesis stop?
When the ribosome reaches a stop codon on mRNA
What was the goal of the Human Genome Project?
The goal of the Human Genome Project was to sequence all of the nearly 3.2 billion nucleotides of the human genome.
What are the three types of RNA made from the DNA template?
What is the composition and function of ribosomes?
Composed of two subunits containing ribosomal RNA and proteins; they synthesize proteins.
What are homologous chromosomes?
Homologous chromosomes are pairs of chromosomes that contain similar genes arranged in the same or almost the same order.
What are the components of the nucleus?
The nucleus consists of a nuclear envelope with pores, nucleoli, and chromosomes, which exist as a tangled mass of chromatin in interphase cells.
What marks the beginning of telophase in mitosis?
Chromosomal movement stops, and the chromosomes uncoil and revert to chromatin form, with nuclear envelopes forming around each chromatin mass.
What happens when the large ribosomal subunit attaches to the small ribosomal subunit–mRNA complex?
It creates a functional ribosome, and the initiator tRNA with its amino acid (methionine) fits into the P site of the ribosome.
What is pre-mRNA?
Pre-mRNA is the initial transcript that includes information from both introns and exons.
What is the S phase?
The S phase is the interval between G1 and G2 during which DNA replication occurs.
What is recombinant DNA?
Recombinant DNA is a combination of DNA from different sources that has been inserted into a host organism to produce proteins it normally does not synthesize.
What is the function of small nuclear ribonucleoproteins (snRNPs)?
snRNPs are enzymes that cut out the introns and splice together the exons in pre-mRNA.
What is cytokinesis?
The division of a cell's cytoplasm and organelles into two identical cells, usually beginning in late anaphase and completed after telophase.
What happens to the two-peptide protein after the formation of the peptide bond?
The resulting two-peptide protein becomes attached to the tRNA at the A site.
What is the role of the P site in a ribosome?
The P (peptidyl) site binds the tRNA carrying the growing polypeptide chain.