Cell Structure Flashcards
Resolution and magnification of a light microscope
Mag: x1500 ; Res: x200nm
Resolution and magnification of electron microscopes
TEM - Mag: x500,000 ; Res: 0.1nm
SEM - Mag: x100,000 ; Res: 0.1nm
Magnification
Degree to which the size of an image is larger than the object itself. Magnification = image size/actual size
Resolution
The degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution, the greater detail you can see.
Staining
Refers to any process that helps to reveal or distinguish different features. In light microscopy, stains may be colours or fluorescent dyes. In electron microscopy, they are metal particles or metal salts.
Magnification equation
Magnification = image size/actual size
Nucleus function
Houses nearly all of the cell’s genetic material. Chromatin consists of DNA and proteins. Has the instructions for making proteins. Chromatin condenses into chromosomes when cells divide.
Nucleolus function
Makes RNA and ribosomes. These pass into the cytoplasm and proteins are assembled at them
Nucleus structure
Largest organelle; shows darkened patches of chromatin when stained. Surrounded by a nuclear envelope.
Nucleolus structure
Dense, spherical, inside the nucleus
Nuclear envelope
Surrounds nucleus. 2 membranes with fluid in between. Nuclear pores go through the envelope, allowing relatively large molecules to exit/enter the nucleus.
Rough endoplasmic reticulum function
Transports proteins that were made on the attached ribosomes. Some may be secreted from cell, others onto the cell surface membrane.
Smooth endoplasmic reticulum funtion
Involved in making the lipids (steroids/other) the cell needs.
Endoplasmic reticulum structure
Series of flattened, membrane bound sacs called cisternae. Continuous with outer nuclear membrane. Rough ER has ribosomes, smooth ER doesn’t
Golgi apparatus function
Receives proteins from ER and modifies them, e.g. adding sugar molecules. Packages the proteins into vesicles to be transported.
Golgi apparatus structure
A stack of membrane bound flattened sacs. Looks like a pile of pitta bread
Mitochondria function
Where ATP is produced during respiration. ATP provides energy for almost all the activities that require it in the cell.
Mitochondria structure
Spherical/sausage shaped. 2 membranes, separated by a fluid filled space. Inner membrane is folded into cristae. Central part is the matrix
Chloroplast function
Site of photosynthesis in plant cells. Light energy is used to drive the reactions of photosynthesis, in which carbohydrate molecules are made from carbon dioxide and water
Chloroplast structure
Only in plant cells and some protoctists. 2 membranes, separated by fluid filled space. Inner membrane is continuous, with a network of flattened membrane sacs called thylakoids.
Stack of thylakoids
A granum (inside chloroplasts). Chlorophyll molecules found here
Lysosome function
Contain digestive enzymes for breaking down materials, e.g. invading microorganisms
Lysosome structure
Spherical sacs, with a single membrane
Ribosome function
Site of protein synthesis. Act as an assembly line where mRNA (from nucleus) is used to assemble proteins from amino acids
Ribosome structure
Tiny organelles. Some in cyoplasm, some on ER. Consist of 2 subunits.
Centrioles function
Take part in cell division. Form fibres known as the spindle, moving chromosomes in nuclear division
Centrioles sructure
Small tubes of protein fibres (microtubules). Pair next to the nucleus of animal cells and in the cells of some protoctists.
Sequence of making a protein
- Instructions in the nucleus, on a gene (on a chromosome)
- mRNA copies the instructions in DNA
- mRNA attaches to ribosome in cytoplasm/on rough ER
- ribosome assembles protein
- protein travels through rough ER
- protein pinched off in a vesicle
- protein arrives at Golgi apparatus
- Golgi packages and modifies the protein (e.g. adding sugars to form glycoprotein)
Types of fibres in cytoskeleton
Actin filaments; microtubules. Made of protein. Keep cell in stable shape and provide an internal framework
Function of actin fibres in cytoskeleton
Like fibres found in muscle, can move against each other. Cause movement in white blood cells, and move organelles around inside the cell
Function of microtubules in cytoskeleton
25nm in diameter, made of protein called tubulin. Used to move microorganisms through liquid/waft a liquid past a cell. Other proteins in microtubules move organelles and other stuff around inside the cell, e.g. chromosomes in mitosis, vesicles. Proteins are called microtubule motors, and use ATP.
Flagella in eukaryotes structure
Correctly called undulipodia. Hair-like extensions from surface of cell. Made of a cylinder of 9 microtubules in a circle, with 2 more microtubules in a central bundle. Longer than cillia
Flagella in eukaryotes function
Forms the tail of the sperm cell, and tail on Trichomonas protoctist. Enables whole cell to move
Cillia structure
Hair-like extensions from surface of cell. Made of a cylinder of 9 microtubules in a circle, with 2 more microtubules in a central bundle. Shorter than undulipodia
Cillia function
Sweeping movement of cillia move substances across surface of cell, e.g. mucus
Flagella in prokaryotes
Look like eukaryotic undulipodia, but are made of a spiral of protein (flagellin). This spins, acting as a motor.
Differences of prokaryotic cells (8)
- only one membrane: cell surface membrane
- no membrane bound organelles (little internal organisation)
- cell wall made of peptidoglycan (murein), not cellulose
- ribosomes are smaller
- DNA is in the cytoplasm in a single loop, a ‘circular chromosome’ and in plasmids
- DNA not surrounded by a membrane. Lies in a general area called the nucleoid (no nucleus)
- ATP production occurs in infolded regions of cell surface membrane called mesosomes
- structure of flagella is different
Differences of plant cells (5)
- Cell wall, made of cellulose
- Plasmodesmata to connect adjacent cells
- Contain a large vacuole
- Contain chloroplasts
- Don’t have microvilli, lysosomes or centrioles
Size of ribosomes
Eukaryotic: 22nm diameter
Prokaryotic: 18nm diameter
Function of cytoskeleton
- provides strength and stability to cell
- moves membrane for endo/exocytosis
- moves organelles around cell and chromosomes in mitosis
- holds organelles in place
- makes up centrioles/spindle fibres
