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Mitosis

MITOSIS Every second, millions of cells in your body are dividing. Some divisions help you grow or heal, while others make the cells needed for reproduction. Let’s break it down. Chromosomes Basics Chromosomes = DNA wrapped around histones, keeping it neat and organized Sister chromatids = identical copies of a chromosome after DNA replication Homologous chromosomes = one from mom, one from dad; same genes but possibly different versions Karyotypes A picture of all your chromosomes, arranged by size and shape 22 pairs of autosomes + 1 pair of sex chromosomes (XX = female, XY = male) Diploid vs. Haploid Diploid (2n) = two sets of chromosomes → body cells Haploid (n) = one set of chromosomes → gametes (sperm/egg) Possible gamete combinations = 2ⁿ (for humans, over 8 million!) The Cell Cycle and Mitosis Interphase: G1 (cell grows), S (DNA copied), G2 (error check) Prophase: chromosomes condense, spindle forms, nucleus breaks down Metaphase: chromosomes l...
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Meiosis

 MEIOSIS Intro .  In most of the cells in your body, new cells are made through mitosis. This process creates exact copies of cells for growth and repair. But when it comes to reproduction, things work differently.Organisms that reproduce sexually—like humans, dogs, trees, and even insects—use a special type of cell division called meiosis Meiosis I  Prophase I Chromosomes condense Homologous chromosomes pair up to form tetrads Crossing over occurs (exchange of genetic material between chromatids) Spindle fibers form Metaphase I Tetrads align randomly at the middle of the cell This random alignment is called independent assortment Anaphase I Homologous chromosomes are pulled to opposite poles Sister chromatids remain attached Telophase I & Cytokinesis Cell divides into two haploid cells Each chromosome still consists of two sister chromatids Meiosis II 1. Prophase II Chromosomes (still made of sister chromatids) cond...
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Mitosis

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Why do cells need to divide? Cells divide for three major reasons: Growth : From a single cell to a whole organism—cell division makes it possible. Repair & Replacement : Lost skin cells? A broken bone? Mitosis steps in to rebuild and replace. Reproduction : Life passes itself on through cell division—either asexually (like bacteria using binary fission) or sexually (via meiosis). Inside the nucleus of a eukaryotic cell, DNA usually exists as a loose tangle called chromatin . But before a cell divides, it bundles that DNA into chromosomes , thanks to proteins called histones . Each chromosome duplicates itself, creating sister chromatids —identical copies joined at a region called the centromere . Humans have: 46 chromosomes in body cells (diploid = 2n) 23 chromosomes in sex cells (haploid = n) Want to see chromosomes? Scientists use karyotypes , which visually arrange chromosomes by size and type. This helps identify the sex chromosomes (XX for females, XY f...
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Protein Synthesis

 What is Protein Synthesis Protein synthesis is essential because proteins are the building blocks of life. They perform nearly all functions in a cell, including: - Building and Repairing Tissues – Proteins make up muscles, skin, and organs. - Enzymes – Proteins act as biological catalysts, speeding up chemical reactions. - Hormones – Some proteins (like insulin) regulate body functions. - Transport – Proteins like hemoglobin carry oxygen in the blood. - Defense – Antibodies help fight infections. Since DNA holds the instructions for making proteins, cells need a process to read these instructions and build the correct proteins. That process is protein synthesis. Before we start protein synthesis we must know what are codons: - Codons - 3 letter mRNA sequence which codes for an Amino Acid  - AntiCodon - tRNA sequence complementary to mRNA’s codons, attaches to the mRNA Protein synthesis happens in two main stages: --> Transcription (in the nucleus) --> Translation (in t...
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DNA replication

DNA is replicated during the cell division process to ensure that the daughter cells get an accurate copy of the genetic information DNA replication: 1. DNA replication starts with an enzyme called Helicase unwinding the DNA strand at a spot called origins of replications 2. Initiator proteins bind to the origin and unwind the strand of DNA 3. The enzyme DNA Helicase unwinds the DNA by breaking the hydrogen bonds between the pairs 4. Single-Strand Binding Proteins bind to the DNA so that it does not coil back up again   5. RNA primase adds a short RNA primer to the single-stranded DNA template.  6. DNA polymerase binds to the RNA primer and begins adding complementary DNA nucleotides to the growing strand in the 5' to 3' direction. This process extends the DNA strand. 7. On the leading strand, DNA polymerase continuously synthesizes the DNA as the replication fork moves along. This strand is synthesized in the same direction as the unwinding. 8. On the lagging strand...
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DNA and RNA intro and experiments

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  What is DNA? DNA is a polymer of four types of nucleotides. Each nucleotide has a deoxyribose sugar, three phosphate groups, and a nitrogen-containing base. The nitrogen containing base is what the DNA is named after. The following are the names of the nitrogen containing bases: adenine (A), guanine (G), thymine (T), and cytosine (C).  DNA structure : A DNA molecule has two chains (strands) of nucleotides running in opposite directions and coiled into a double helix. Covalent bonds link the deoxyribose (sugar) of one nucleotide to a phosphate group of the next, forming the sugar–phosphate backbone of each chain. Hydrogen bonds between the internally positioned nitrogenous bases hold the two strands together. Chargaff’s first rule : First, the amounts of thymine and adenine are identical in any DNA molecule, as are the amounts of cytosine and guanine (A = T and G = C). We call this discovery Chargaff ’s first rule Experiments with DNA :  Griffith - F irst experiment sho...
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Photosynthesis

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What is Photosynthesis?  Photosynthesis is the process by which plants convert the products of Cellular Respiration (Water and Glucose) into sugar and oxygen Step 1: Light Dependent Reactions --> Take place in Thylakoid Membranes First the chlorophyll in the plants absorb sunlight which excites electrons and moves them to a higher energy state. Once the electrons have been excited, they start the ETC (Electron Transport Chain) which generates energy Since the electrons are transferred in the ETC, chlorophyll must recoup the electrons that it has lost, so the water molecules are broken down into oxygen , H+ ions, and electrons (oxygen is a byproduct and it exits the cycle) The energy released from the ETC is used to pump the H+ ions across the membrane, creating a difference in the number of H+ ions on both sides of the membrane (proton gradient) Due to the creation of the proton gradient, protons try to get back to the other side of the membrane in an effort to  (this is d...
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