AS1 MEMBRANOUS ORGANELLES

nucleus

  • largest most prominent organelle of the cell
  • it controlls the cells activity and retains the organisms hereditary material (DNA)
  • it sboyunded by the nuclear envelope, a double membrane of which the outer is continuous with the endoplasmic reticulum
  • the inner membrane has 3 proteins on its surface whcih act as anchoring points for chromosomes during interphase
  • it has many large pores which allow the passage of large molecules such as RNA betwen the nucleus and the cytoplasm
  • the material inside the nucleus is called the nucleoplasm whcih contains chromatin (DNA bound to histone protein)
  • during interphase they condense to fome chromosomes
  • the denser areas of chromatin are called heterochromatin and the more sparesly areas are called euchromatin
  • within the nucleus there are one or two small bodies called the nucleolus, they manufacture rRNA and form ribosomes
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mitochondrion

  • found in the cytoplasm of most eukaryotic cells but may be absent in highly specialised ells such as red blood cells
  • they are bounded by a double membrane, the outer controls the entry and exit of chemicals and the inner is folded into a series of folds giving cristae
  • they increase surface area on which respiratory reactions occur
  • the remainder of the mitochondria is the matrix which is a semi ridgid material containing protein, lipids and traces of DNA and sometimes mitochondrial ribosomes
  • they produce ATP by functioning as sites for certain stages of respiration
  • the number of cristae increases in metabolically active cells which in turn increases the number of respiratory enzymes on the surface e.g.sperm cells
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endoplasmic reticulum

  • an elaborate system of membranes folded throughout the cell giving it a cytoplasmic skeleton
  • its an extenion of the outer nuclear membrane which is continuous
  • the membranes form a series of sheets which enclose flattened sacs called cisternae
  • there are 2 types

1. rough endoplasmic reticulum- they are lined with ribosomes and are envolved with protein synthesis and are most abundant in cells which secrete enzymes or are growing. If the cell has been damaged there is an increased production of RER to produce the proteins needed for the cells repair

2.smooth endoplasmic reticulum- when the ER lacks ribosomes they are concenred with lipid synthesis and are most abundant in lipid related secretions such as sebaceous glands

  • they provie a large surface area for chemical reactions, are involved with trasport of materials, producing proteins, lipids and forming lytic enzymes
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golgi apparatus

  • similar structure to the ER but more compact
  • its made of stack of flattened sacs of membranes, the sacs are fluid filled and pinch off vescicles
  • nirmally only one per cell but there may be a large number of stacks known as dictyosomes
  • all proteins produced by the RER are passed through the golgi, they first pas though the cis-golgi network which returns any proteins that have been wrongly exported to the RER, they then pass though the stack of cisternae which modify the proteins and lipids undergoing transport and adding markers to allow them to be identified and sorted at the trans-golgi network which sorts the proteins and lipids and sends them to thier final destinsation
  • they form glycoproteins, produce secretoey enzymes, form lysosomes, secrete carbohydrates and transport and store lipids
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lysosomes

  • sperical bodies containing around 50 enzymes (including lytic enzymes) mostly hydrolases in acid solution
  • these enzymes are isolated here to prevent them from acting on other things in the cells that dont need brokend down
  • they digest material which the cell ocnumes from the environment,the material is broken down within the lysosome
  • they digest parts of the cell such as worn out organelles (autophagy) after the death of the cell the lysosomes are responsible for their compelte breakdown (autolysis)
  • they release enzymes outside the cell in order to break down other cells
  • they are especially abundant in secretory cells and phagocytic white blood cells
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microbodies (peroxisomes)

  • small spherial membrane bound bodies
  • they have no internal structure appart from being slightly granular
  • they contain a number of metabolically important enzymes such as catatlase whcih breaks down hydrogen peroxide to water and oxygen
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vacuole

  • fluid filled sac bounded by a single membrane (tonoplast), usually one per mature plant cell
  • it contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins
  • the sugars and amino acids act as a temporary foods store for the cell
  • anthocyanins may attract pollinating insects to the petals
  • they act as temporary stores for organic wastes such as tannins which may accumulate in the vacuoles of leaf cells and when they fall they are removed
  • they support herbaceuos plants by providing an osmitic system of creating a pressure potential
  • in animal cells the vacuoles are much smaller but may occur in larger numbers
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chloroplast

  • they belong to a larger group of organelles called platids
  • they are bounded by a double membrane (chloroplast envelope), the outer membrane has a similar structure to the plasma membrane and the inner is folded into lamells and is highly selective with what it lets in and out
  • within th chlorplast there are 2 distinct regions, the stroma is a colourless gelatinous matrix in which grana are embedded
  • each granum s made of between 2 and 100 closed flattened sacs called thylakoids which contain photosynthesetic pigments such as chlorophyll
  • some thylakoids have tubular extensions which interconnect adjacent grana
  • in the stroma there are a series of starch grains which are temporary stores for the products of photosynthesis
  • a small amount of DNA is always present in the stroma aswell as oil droplets
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