Cytology Lesson Notes PDF

# Cytology ## Subject of Lesson 3 ### Date / / Cytology is a branch of biology that studies the composition and organization of the cell. ## Characteristics of Living Organisms - **Use of Energy:** Living organisms constantly need energy to perform their vital activities. - **Growth:** The bodie...

# Cytology ## Subject of Lesson 3 ### Date / / Cytology is a branch of biology that studies the composition and organization of the cell. ## Characteristics of Living Organisms - **Use of Energy:** Living organisms constantly need energy to perform their vital activities. - **Growth:** The bodies of living organisms gradually increase in size. - **Reproduction:** All living organisms are capable of producing similar individuals. - **Response to Environment:** Living organisms must sense, interact, and respond to their surrounding environment. ## Basis of Structure: - Living organisms are made up of small units called cells, which modify and adapt according to their functions. - A group of similar cells can unite to form tissue. - Many tissues integrate to give an organ. - Many organs combine to make a system. - The relationship between cell, tissue, organ, and system is as follows: - Cell - Molecules - **Cytology** - **Molecular Biology** - **Histology** - Tissue - Organ - System - **Anatomy** - **Physiology** ## Metazoa ### Many Cell Types Perform Different Functions - **Human:** الإنسان - **Parazoa:** All cells perform all functions. - **Sponges:** الإسفنجيات - **Protozoa:** A single cell performs all functions. - **Amoeba:** الأميبا - **Cells differ in shape, size, and structure to adapt functions**. - The human body may be composed of over 75 trillion cells. - Just one drop of human blood contains about 5 million red blood cells. - Due to the division of labor, cells display many different types of cells that differ in shape, size, structure, and modifications to adapt their function. - The human body has over 200 different types of cells. ## Animal Cell - **Fibrils** - **Karyolymph** - **Nucleolus** - **Nucleus** - **Mitochondria** - **Plasma Membrane** - **Lysosomes** - **Cytoplasm** - **Endoplasmic Reticulum (ER)** - **Ribosomes** ## Protoplasm - **Protoplasm:** Cytoplasm + Nucleoplasm - **Cytoplasm:** Cytosol + cell organelles, except the nucleus. - **Cytosol:** The fluid part of the cytoplasm. ## Cell Components - **Nucleus:** contains genetic material - **Plasma membrane:** surrounds the cell - **Cytoplasm:** contains organelles and other cell components - **Envelope** ## Interphase Nucleus (Interphase Neucleus)) نواة الطور البيني - **RNA** ## Gene Transcription & Information Flow - **DNA** Transcription نسخ - **mRNA** Translation ترجمة - **Protein:** - "Enzymes" - The functional state of the cell can be affected by mutations and toxins, leading to problems with material accumulation in the cell. ## Cell Division - **Telomeres:** - **Centromere:** - **Sister Chromatid:** arm ## Genetic Material - **Ribose Sugar:** CH₂OH - **Deoxyribose:** CH₂OH - **DNA = Deoxyribonucleic Acid:** - **A = T** - **C = G** ## Genome - **Genome:** All DNA in the cell. - **Distance between two sets of DNA = 0.34A:** - **Length of DNA: 0.34A x 32 = (1.5 - 2) meters**: - Due to the length of DNA, it needs to shorten in order to fit in the nucleus. ## Specific Protein - **Squance:** - **125000 genes:** - **P-Value of H:** - **High base:** قاعدي - **Acidic:** حامضى ## Nucleosome Unit - **Nucleosome:** - Formed by wrapping 146 bp around a highly basic protein called histone. - Consists of 4 "cores." - Contains 8 histone fragments. ## Central Dogma - **Central dogma of cytology and molecular biology:** - DNA **Transcription** (copying) - mRNA **translation** (interpreting) - **cell-specific protein**. - Interphase Nucleus: "interphase nucleus" ## Central Dogma Details - **DNA doesn't leave the nucleus:** لانغادر النواة - **Reverse transcription:** - **RNA** to **DNA:** - **Replication occurs prior to cell division:** - The number of chromosomes increases from 46 to 92. - **Central dogma as a relationship between the three major molecules that form the basis of inheritance:** - Genome: "100%" - Cell Specific: "100%" - Euchromatin: 2% - Gene Expression: - The role of transcription is to modify the genetic code. - **mRNA** to **DNA:** ## Gene Expression - Takes place in the nucleus. - Copies small sequences of mRNA. - **Procedure:** - **1:** DNA strand unwinds, facilitated by **helicase**. - **2:** **RNA polymerase** fits the nucleotide of mRNA. - **3:** - **Non-sense Strand:** 5 → 3 - **Sense Strand:** 3 → 5 - **4:** **5' (G) mRNA (mature)** - **5:** mRNA is transcribed by **RNA polymerase**. - **promoter** - **termination region** - **introns:** exons ## Post-Transcriptional Modifications - **Splicing:** The process by which introns are removed and exons are joined. - **Intron:** a segment of DNA does not translate, but regulates the activity of the protein. - **Exon:** a segment of DNA that is translated and forms a protein. ## Additional Notes - **7-Methyl Guanosine:** - **Poly adenylation:** The addition of a polyA tail (100-250) to the mRNA. - **Capping:** - **GMP + P → GDP** - **GDP → P + Energy** ## Benefits of Modifications - **Increase lifespan**: - **Protect the mRNA molecule from degradation:** - Once the mRNA is ready to leave the nucleus, the three operations mentioned above happen. ## Nuclear Pore of Nuclear Membrane: - These processes allow the mRNA to move out of the nucleus, but without them, the mRNA cannot leave. # Cell Division ## Subject of Lesson 3 ### Date / / - Cell division is the process by which a cell divides into two new cells (daughter cells). - The three types of cell division for cell reproduction are: - **Direct Cell Division:** Simple binary fission that occurs in prokaryotes. - **Mitosis:** Occurs in all somatic eukaryotic cells; it replaces worn-out or damaged cells. - **Meiosis:** Occurs in gonads to produce gametes (sex cells). ## Cell Cycle - **Interphase:** - The growth phase, where DNA duplicates and organelles double. - 93% of a cell’s life is spent in interphase. - It takes place in three phases: - **G₁ Phase:** Cells mature and increase in size. - **S Phase:** Chromosomes are replicated. - Two strands known as "sister chromatids" are joined by a centromere. - **G₂ Phase:** Organelles double and a new cytoplasm begins to form. ## Mitosis - The process by which the nucleus divides into two identical nuclei. - **Two main steps:** - Mitosis: - Nuclear division takes place in four phases (PMA). - **Prophase** → **Metaphase** → **Anaphase** → **Telophase** - **Cytokinesis:** - The cytoplasm divides, forming two new cells. - **Phases of mitosis:** - **Prophase:** - Chromosomes become visible and condensed (sister chromatids). - Two centrioles migrate to the poles. - **Metaphase:** - Spindle fibers attach to a protein structure on the centromere of each chromosome. - Chromosomes line up in the middle (equator) of the cell, moved by the spindle. - **Anaphase:** - Centromeres join the sister chromatids, which are then split. - Sister chromatids separate, becoming individual chromosomes. - Separate chromatids move to the opposite poles of the cell. - **Telophase:** - The last phase of mitosis, it consists of four steps: - Chromosomes (each consisting of a single chromatid) uncoil. - A nuclear envelope is formed at each pole of the cell. - Spindle fibers break down and dissolve. - Cytokinesis begins. ## Cytokinesis - Occurs at the end of mitosis. - The division of the cytoplasm to form two new daughter cells. - Organelles are divided. - A groove (cleavage furrow) forms from outside to inside, pinching the parent cell into two daughter cells. ## Meiosis - The process of cell division in which gametes are formed, halving the number of chromosomes. - This process leads to sexual reproduction and zygote formation. - **Zygote:** Fertilized egg which has a diploid number of chromosomes. - **Phases of meiosis:** - Similar to mitosis, but meiosis includes eight phases and splits the cell division into two parts: - **Meiosis 1:** - **Prophase 1:** - Homologous chromosomes come together, and the four chromatids overlap to form a tetrad. - It can be subdivided into five substages: - **Leptotene:** Initial stage of condensation. - **Zygotene:** Synapsis of homologous chromosomes. - **Pachytene:** Recombination (crossing over). - **Diplotene:** Chiasmata (sites of crossing over) become visible. - **Diakinesis:** Chiasmata are terminalized. - **Metaphase 1:** - Homologous chromosomes line up at the equator of the cell. - Since humans have 23 pairs of chromosomes, meiosis results in 8,388,608 possible combinations of chromosomes (2²³). - **Anaphase 1:** - Spindle fibers attach to the centromeres of each pair of chromosomes, and homologous chromosomes separate to opposite ends of the cell. - Centromeres do not split like they do in mitosis. - Each cell receives one chromosome from each homologous pair. - **Telophase 1:** - Spindle fibers break down. - Chromosomes uncoil. - Cytoplasm divides through cytokinesis. - Further cell division is needed because the number of chromosomes was not reduced. - A short interphase may occur after telophase I, but it is important to note that if a cell does have a second interphase, there is no replication of chromosomes. - **Meiosis 2:** - **Prophase 2:** - Chromosomes condense. - Spindle fibers form. - **Metaphase 2:** - Chromosomes align on the metaphase plate. - **Anaphase 2:** - Sister chromatids separate, and chromosomes move to opposite ends of the cell. - **Telophase 2:** - Chromosomes uncoil. - Nuclear envelopes form. - Cytokinesis occurs, producing four haploid daughter cells. - **Homologous Chromosomes:** - Two separate chromosomes, one from the mother and one from the father. - They have the same length and carry the same genes. ## DNA Replication - DNA replication does not occur between meiosis stages 1 and 2. - **Meiosis II:** - **Division of chromatids:** The number of chromosomes is reduced by half. - **Phases:** - Prophase II - Metaphase II - Anaphase II - Telophase II ==End of OCR==