biology topic 2


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  • Created on: 23-03-16 11:28
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  • Biology Topic 2
    • Cells
      • Eukaryotic
        • complex
        • Includes all animal and plant cells
        • Parts of cell
          • Nucleus
            • A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores.
            • Chromatin is made from proteins and DNA. The pores allow substances to move between the nucleus and cytoplasm
            • Contains the nucleolus
              • Makes Ribosomes
          • Lysosome
            • A round organelle surrounded by a membrane, with no clear internal structure
            • Contains digestive enzymes. These are kept separate from the cytoplasm by the surrounding membrane, but can be used to digest invading cells or to break down worn out components of the cell
          • Vesicle
            • A small fluid filled sac in the cytoplasm, surrounded by a membrane
            • Transports substances in and out of the cell and between organelles. Some are formed by the Golgi apparatus or the endoplasmic reticulum, while others are formed at the cell surface
          • Endoplasmic reticulum
            • Smooth endoplasmic reticulum is a system of membranes enclosing a fluid filled space
              • Function: Synthesises and processes lipids
            • Rough endoplasmic reticulum is similar to the sER but covered in ribosomes
              • Function: Folds and processes proteins that have been made at the ribosomes
          • Golgi Apparatus
            • A group of fluid-filled flattened sacs, vesicles are often seen at the edges of the sacs
            • It processes and packages new lipids and proteins. It also makes lysosomes
          • Centriole
            • Hollow cylinders, containing a ring of microtubules (tiny protein cylinders)
            • Involved with the separation of chromosomesduring cell division
          • Mitochondrion
            • They're usually oval-shaped. They have a double membrane-inner one is folded to form structures called cristae. Inside is the matrix, which contains enzymes involved in respiration
            • The site of aerobic respiration. Where ATP is produced. They're found in large numbers in cells that are very active and requires a lot of energy
        • 1. Proteins are made at the ribosomes 2. The ribosomes on the rER make proteins that are sxcreted or attached to the cell membrane. The free ribosomes in the cytoplasm make proteins that stay in the cytoplasm         3. New proteins produced at the rER are folded and processed in the rER (sugar chains etc)                  4. They are then transported from the ER to the Golgi-Apparatus in vesicles            5. At the Golgi-Apparatus, the proteins may undergo further processing (sugar cains are trimmed and added etc)                  6. The proteins enter more vesicles to be transported around the cell.
      • Prokaryotic
        • Include bacteria and blue-green algae
    • Cell Organisation
      • Similar cells grouped together to make tissues
    • The cell cycle and Mitosis
      • Process of cell growth and division
      • Gap Phase 1 (G1): Cell grows and new organelles and proteins are made.
        • Synthesis (S1): Cell replicates its DNA, ready to divide by mitosis
          • Gap Phase 2 (G2): Cell keeps growing and proteins needed for cell division are made.
            • Mitosis: The cycle starts and ends here
              • Used for...
                • Growth
                • Repair
                • A-Sexual Reproducton
              • 4 Phases
                • Interphase: Cell carries out its normal functions, but also prepares to divide. The cell's DNA is unravelld and replicated, to double its genetic content. The organelles are also replicated so it has spare one, and its ATP content is also increased.
                • 1. Prophase: The chromosomes condense, getting shorter and fatter. The centrioles start moving to the opposite ends of the cell, forming a network of protein fibres across it called spindle. The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.
                  • 2. Metaphase: The chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.
                    • 3. Anaphase: The centromeres divide, separating each pair of sister chromatids. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first.
                      • 4. Telophase: The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again. They're now called chromosomes again. A nuclear envelope forms around each group of chromosomes, so there are now two nuclei. The cytoplasm divides and there are now two daughter cells that are genetically identical to the original celland to each other. Mitosis is finished and each daughter cell starts the interphase part of the celcycle, ready for the next round of mitosis
      • Meiosis
        • 1. DNA replicate so there are two identical copies of each chromosome, called chromatids.
          • 2. The DNA condenses to form double-armed chromosomes, made from two sister chromatids.
            • 3. The chromosomes arrange themselves into homologous pairs-pairs of matching chromosomes
              • 4. First division-the homologous pairs are separated, halving the chromosome number
                • 5. Second division- the pairs of sister chromatids are separated
                  • 6. Four new cells (gametes) that are genetically different from each other are produced
        • Crossing over of chromatids
          • 1. Before the first division of meiosis, homologous pairs of chromosomes come together and pair up
            • 2. Two of the chromatids in each homologous pair twist around each other
              • 3. The twisted bits break off their original chromatid and rejoin onto the other chromatid, recombining their genetic material
                • 4. The chromatids still contain the same genes but they now have a different combination of alleles
                  • 5. This means that each of the four new cells formed from meiosis contains chromatids with different alleles
        • Independant assortment of chromosomes
          • 1. The four daughter cells formed from meiosis have completely different combinations of chromosomes
            • 2. All your cells have a combination of chromosomes from your parents, half from your mother (maternal), half from your dad (paternal)
              • When the gametes are produced, different combinations of those maternal and paternal chromosomes go into each cell
                • This is called independent assortment (separation) of the chromosomes

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