Active Transport, Chromosomes, & Cell Cycle

• Study notes on Active Transport, Chromosomes, and the Cell Cycle

Active Transport

• Active transport involves moving substances against the concentration gradient.
• Substances move from an area of low concentration to an area of high concentration.
• Molecular transport moves molecules across cell membranes and within cells, or it moves ions across the cell membrane through carrier proteins activated by ATP against the concentration gradient.
• Bulk transport moves large amounts of substances or cells against the concentration gradient.
• Endocytosis is a type of bulk transport where the cell takes in or engulfs a substance or another cell by extending its cellular membrane and incorporating the substance into the cytoplasm.
• Exocytosis is a bulk transport process where a cell releases particular contents via vesicles as a transport system.

Chromosomes

• Chromosomes are rod-shaped structures, observable in the nucleus during cell division, composed of deoxyribonucleic acid (DNA) and proteins.
• DNA contains hereditary instructions for creating new organisms, known as genes.
• Chromatin, composed of DNA, RNA, and proteins, forms chromosomes in the nucleus of a cell and consists of nucleosomes.
• Nucleosomes are DNA strands wrapped around histones.
• RNA transmits genetic information.
• A gene is a section of DNA that stores an organism's genetic information.
• The centromere is part of a eukaryotic chromosome.
• The region of a chromosome holding two sister chromatids is the centromere.
• The kinetochore is a protein structure that forms on top of the centromere, serving as the attachment site for spindle fibers during cell division.
• The telomere is a region of repetitive DNA sequences at the end of a chromosome that protects the ends from fraying or tangling and gets smaller each time the cell divides.
• Nucleic acids are made of carbon, hydrogen, oxygen, nitrogen, and phosphorus
• Nucleic acids are a monomer (building blocks)
• Nucleotides consist of a nitrogen-containing base attached to a pentose sugar, which is attached to a phosphate group.
• A phosphate group is made of 1 phosphorus and 4 oxygen and provides structural support.
• Pentose sugar is a five-carbon sugar used to distinguish DNA and RNA.
• A nitrogenous base contains nitrogens and has the chemical properties of the base.

Chromosome Classification

• Autosomes are DNA sections that carry most genetic information and typically determine traits.
• Allosomes, also called sex chromosomes, determine gender through X and Y chromosomes.
• Males have one X and one Y chromosome, while females have two X chromosomes.
• A karyogram visually represents a cell's chromosomes and identifies the number, size, shape, and structure of chromosomes.
• Karyotyping is a technique used to detect chromosomal abnormalities, helps doctors with genetic conditions, aids in studying genetics, and is typically used in metaphase when chromosomes are most visible.
• Aneuploidy is an abnormality in the number of chromosomes.
• Monosomy is a missing chromosome (45 chromosomes).
• Trisomy is an extra copy of a chromosome (47 chromosomes).
• Monosomy X (Turner syndrome) results in sex characteristics that fail to develop properly.
• Traits of Monosomy X include: lack of height, difference in sexual development, broad chest and small lower jaw.
• Trisomy 21 (Down Syndrome) is the most common chromosome abnormality.
• Traits of Trisomy 21 include: upward slant of the eyes, round facial shape, short stature, a delay in development, and a learning disability.
• Trisomy XXY (Klinefelter Syndrome) is a common chromosomal abnormality alongside Down syndrome.
• Traits of Trisomy XXY include: tall stature, reduced muscle, delayed/incomplete puberty, small testes, and infertility.

The Cell Cycle

• The cell cycle is a series of events that lead to cell division and duplication that comprises a series of phases a cell undergoes to grow and divide.
• The cell cycle consists of 3 stages: Interphase, the M-phase and cytokinesis
• Interphase involves the cell multiplying and copying its DNA.
• Cells spend the majority (90%) of their life in Interphase.
• Interphase can be broken down into 3 stages: Growth 1 (G1) phase, Synthesis phase (S-Phase) and Growth 2 (G2) Phase
• During the Growth 1 (G1) phase, the cell grows in size and synthesizes proteins and organelles necessary for normal cellular functions, ensuring conditions are favorable for DNA replication.
• During the Synthesis phase (S-Phase), DNA replication occurs to duplicate each chromosome, producing two sister chromatids while the cell continues to produce proteins and other molecules needed for DNA packaging and repair.
• During the Growth 2 (G2) phase, the cell undergoes further growth, produces proteins and organelles required for mitosis, checks the replicated DNA for errors, and repairs any damage before proceeding to mitosis.
• Growth 0 (G0) phase occurs outside of interphase where the cell exits the and enters a state where it is neither dividing nor preparing to divide
• Apoptosis is when the damaged DNA can no longer be repaired and is a controlled process that eliminates damaged or unnecessary cells to maintain tissue health and homeostasis.
• The next stage of the cell cycle is the Mitotic Phase/M-Phase where the nucleus divides via mitosis and miosis
• Mitosis is a form of nuclear division to form two identical daughter cells with the same number of chromosomes as the parent nuclei over 4 stages: prophase, metaphase, anaphase, and telophase.
• During prophase, the nuclear envelope disintegrates, chromosomes condense and become visible,and spindle fibers form at the cell's opposite poles and the kinetochore proteins connect the centromere to spindle fibers and become visible
• The chromosome count is diploid (2n), meaning two sets of chromosomes for each parent are found in a cell
• During metaphase, the chromosomes align at the center of the cell at the metaphase plate, the spindle fibers are fully formed, and the chromosomes are pulled tightly by the spindle fibers while the sister chromatids of each chromosome remain joined.
• During anaphase, the spindle fibers pull on the chromosomes from both poles of the cell and the sister chromatids separate
• During telophase, the nuclei form around the chromosomes and get a copy of each chromosome in the form of chromatids
• Each nucleus has a diploid number of chromosomes and the cell prepares to divide into two daughter cells
• Cytokinesis is when the cell physically splits into two daughter cells, the nuclear envelope reforms, and each cell has a diploid number of chromosomes.
• Meiosis is a form of cellular division that produces daughter nuclei containing half the number of chromosomes, or haploid (n), as the parent nucleus
• Meiosis occurs only in gametes (sperm and egg cells).
• At the end of meiosis, the number of chromosomes reduces from diploid to haploid to produces four (4) haploid (n) daughter cells and increases genetic diversity through recombination and independent assortment.
• The entire process of meiosis can be broken down into two (2) parts: Meiosis I and Meiosis II, each with prophase, metaphase, anaphase, and telophase
• Prophase I involves the nuclear envelope disintegrates
• Chromosomes condense and become visible
• Spindle fibers, made up of microtubules, form at the cell's opposite poles
• Kinetochore is formed and homologous chromosomes pair up (synapsis) and exchange genetic information (crossing over)
• The cell contains a diploid (2n) number of chromosomes
• metaphase I Involves the homologous chromosomes align at the metaphase plate and chromatids from two homologous chromosomes are now different from each other
• The fully formed spindle fibers pull the homologous chromosomes tight
• The sister chromatids of each chromosome remain joined - the cell checks for any alignment errors and corrects them, and the chromosome count is diploid (2n)
• During anaphase I, the spindle fibers attached to the kinetochores pull the homologous chromosomes to opposite ends of the cell, and the chromosome count is diploid (2n).
• During telophase, the nuclei form around the homologous chromosomes, and the chromosome count is haploid (n).
• During cytokinesis, the cell physically splits into two cells, the nuclear envelope reforms, and the cell has a haploid (n) chromosome count while proceeding to undergo interkinesis and does not undergo DNA replication.
• During prophase II, chromosomes condense and the nuclear membrane disintegrates, the nuclear envelope disintegrates, spindle fiber forms at the cell's opposite poles, the kinetochores are formed and chromosome Count is haploid(n)
• During metaphase II, chromosomes align in a spindle file at the metaphase plate, the fully formed spindle fibers pull the homologous chromosomes tight, the sister chromatids of each chromosome remain joined, the cell checks for any alignment errors and corrects them and the chromosome count is haploid (n)
• During anaphase II, the sister chromatids are separated and pulled to opposite poles of the cell, and the chromosome count in haploid (n)
• During telophase II, the cell divides, resulting in four genetically unique daughter cells, and each daughter cell has one copy of each chromosome.
• During cytokinesis, the cell physically splits into two cells, the nuclear envelope forms, and each gamete has a haploid (n) chromosome count.