Cell Biology - Cell Structures

Cell Structures Mitochondria Double membrane structure. Inner membrane will have folds called Cristae. Function is to carry out cellular respiration to produce ATP (our energy currency). Lysosomes Spherical, contains hydrolytic (digestive) enzymes called lysozymes to catalyse the hydrolysis of various bonds. Also involved in apoptosis (controlled cell death). Peroxisomes Spherical and contains catalase enzymes to break down hydrogen peroxide, which is toxic to the body, into oxygen and water. Hydrogen peroxide can create a lot of free radicals which can cause oxidative stress and lead to cell death. Cilia and Flagella Hair-like structures that extend off the surface of cells. Called cilia when they are large in number and small. Called flagella when they are less numerous and longer. They are composed of 9 pairs of microtubules arranged around a central pair. Function is to aid cell movement. Centrioles Composed of 9 sets of triplet microtubules arranged in a ring, and they exist in pairs. Serve as the skeletal system and help to determine the location of the nucleus and other organelles as they are like scaffolding. Also help form cilia during interphase and to form spindles which is essential for cell division. Plastids Present only in plant cells. 3 types: Chloroplasts, chromoplasts (synthesizes and stores pigments) and leucoplasts (stores food such as starches, proteins, and lipids). Chloroplasts Oval, double membrane that contains stacked sacs called thylakoids (individuals are called granum) which contain chlorophyll, a green photosynthetic pigment. Carries out photosynthesis (conversion of light energy to chemical energy). Stroma is a fluid in the internal space that surrounds the thylakoids. Plant vs animal cells: Animal cells don’t contain chloroplasts. Animal cells do not have cell walls. Vacuoles in plants are larger than animal cell vacuoles. In animal cells, there may be multiple scattered around. Cell Cycle: Function is for the cell to grow and divide. Interphase is the period of growth that occurs between cell divisions. Prokaryotes: DNA replication starts once the prokaryote has grown to a certain size. This is followed by binary fission, which is asexual reproduction. 2 genetically identical daughter cells are produced. Eukaryotes: Interphase consists of G1, S and G2. This is followed by the M phase (mitotic cell division). The M phase has prophase, metaphase, anaphase and telophase. This is followed by cytokinesis (division of the cytoplasm). Cell differentiation is a process where the cell specialises. It changes its shape, size and energy requirements, and this is an irreversible process. They can differentiate into: germ cells (reproductive), somatic cells (anything other than gametes) and stem cells. Embryonic stem cells are found in human blastocyst, an early stage of embryo development. Adult stem cells are found in bone marrow, and can be differentiated into many, but not all, types of cells. The more cells it can specialise into, the higher the potency. Totipotent: they can differentiate into all types of cells. Pluripotent: they can differentiate into nearly all types of cells. Multipotent: they can differentiate into a closely related family of cells, e.g., renal cells. Oligopotent: they can differentiate into a few cells. Unipotent: can only produce cells of their own type, but their self-renewing property allows them to be categorised as a stem cell.