hard Flashcards
bases
A,G-Purines. C,T-pyrimidines always bond with each other, a-t is two hydrogen bonds between each other. c-g is always three
mutagenic agents
increase error rate-carcinogenic agents are sub category, cause mutations in genes to do with cell cycle
dna code
-non overlapping-each base triplet is read in sequence, seperate from the triplet before and after it -degenerate-some AA coded for by more than one base triplet -universal-same specific base triplets code for the same AA in all living things
mutations
point mutation-change in one base
missense mutation-base change changes AA-could affect tertiary structure
silent mutation-no change to AA because new triplet codes for same AA-because code is degenerate
nonsense mutation-cuts short the protein-truncated protein-too short- because triplet changes to stop codon-ribosome stops adding AA
indel mutation-frameshift mutation, base is added or deleted
Name organelles in animal and plant cell
animal-plasma (cell surface membrane)
-RER
-nucleolus
-nucleus
-SER
-lysosome
-ribosome
-nuclear envelope
-golgi apparatus
cytoplasm
-mitochondrion
-Plant cell has same but few added extras
-cell wall with plasmodesmata
-vacuole (contains cell sap)
-chloroplasts
organelles
plasma(cell surface) membrane-The membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells. It’s made mainly of lipids and protein.-Regulates the movement of substances into and out of the cell.
It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
cell wall-A rigid structure that surrounds plant cells. It’s made mainly of the carbohydrate cellulose.-supports plant cells
nucleus-A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. The nucleus contains chromatin (which is made from DNA and proteins) and a structure called the nucleolus.-The nucleus controls the cell’s activities (by controlling the transcription of DNA - see page 40). DNA contains instructions to make proteins
— see page 38. The pores allow substances (e.g. RNA) to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes (see below).
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, and can be used to digest invading cells or to break down worn out components of the cell.
ribosome-A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum.
It’s made up of proteins and
RNA (see page 34). It’s not surrounded by a membrane.-The site where proteins are made.
rough endoplasmic reticulum-A system of membranes enclosing a fluid-filled space. The surface is covered with ribosomes.-Folds and processes proteins that have been made at the ribosomes.
smooth endoplasmic reticulum-Similar to rough endoplasmic reticulum, but with no ribosomes.-Synthesises and processes lipids.
vesicle-A small fluid-filled sac in the cytoplasm, surrounded by a membrane.-Transports substances in and out of the cell (via the plasma membrane) and between organelles. Some are formed by the Golgi apparatus or the endoplasmic reticulum, while others are formed at the cell surface.
-golgi apparatus-A group of fluid-filled,
membrane-bound, flattened sacs.
Vesicles are often seen at the edges of the sacs.-It processes and packages new lipids and proteins.
It also makes lysosomes.
mitochondrion-They’re usually oval-shaped.
They have a double membrane
— the 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 require a lot of energy.
chloroplast-A small, flattened structure found in plant cells. It’s surrounded by a double membrane, and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of the chloroplast to form grana. Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane.-The site where photosynthesis takes place. Some parts of photosynthesis happen in the grana, and other parts happen in the stroma (a thick fluid found in chloroplasts).
centriole-Small, hollow cylinders, made of microtubules (tiny protein cylinders). Found in animal cells, but only some plant cells.-Involved with the separation of chromosomes during cell division
cilia-Small, hair-like structures found on the surface membrane of some animal cells. In cross-section, they have an outer membrane and a ring of nine pairs of protein microtubules inside, with two microtubules in the middle. 9+2 formation-The microtubules allow the cilia to move. This movement is used by the cell to move substances along the cell surface.
flagellum-Flagella on eukaryotic cells are like cilia but longer. They stick out from the cell surface and are surrounded by the plasma membrane. Inside they’re like cilia too — two microtubules in the centre and nine pairs around the edge.-The microtubules contract to make the flagellum move.
Flagella are used like outboard motors to propel cells forward (e.g. when a sperm cell swims).
info
ribosomes on RER make proteins that are excreted or attached to cell membrane. Free ribosomes in cytoplasm make proteins that stay in cytoplasm. folded and processed in RER and then transported to Golgi in vesicles
-cytoplasm-has network of protein threads running through it-cytoskeleton
-cytoskeletal protein filaments
-resolution is how well a microscope is able to distinguish between two points that are close together. If a microscope lens can’t separate two objects, then increasing the magnification wont help.
4 main functions cytoskeleton
1)microtubules and microfilaments support the cells organelles, keeping them in position.
2)They also help to strengthen the cell and maintain its shape
3)they’re also responsible for movement of materials within the cell, eg movement of chromosomes when they separate during cell division depends on contraction of microtubules in spindle.
4)Proteins of cytoskeleton can also cause cell to move eg movement of cilia and flagella is caused by cytoskeletal protein filaments that run through them
cytoskeleton is dynamic-constantly changing which allows it to respond to changes in the cell and carry out its functions
prokaryotes vs eukaryotes
prokaryotes-
Extremely small cells (less than 2 um diameter)
DNA is circular
No nucleus — DNA free in cytoplasm
Cell wall made of a polysaccharide, but not cellulose or chitin
Few organelles and no membrane-bound organelles, e.g. no mitochondria
Flagella (when present) made of the protein flagellin, arranged in a helix
Small ribosomes
eukaryotes-
Larger cells (about 10-100 pm diameter)
W
DNA is linear
Nucleus present — DNA is inside nucleus
No cell wall (in animals), cellulose cell wall (in plants) or chitin cell wall (in fungi)
Many organelles - mitochondria and other membrane-bound organelles present
Flagella (when present) made of microtubule proteins arranged in a ‘9 + 2’ formation
Larger ribosomes
Microscopes
1) Light microscopes use light (no surprises there).
2) They have a lower resolution than electron microscopes — they have a maximum resolution of about 0.2 micrometres (um). So they’re usually used to look at whole cells or tissues.
3) The maximum useful magnification of a light microscope is about × 1500.
=
Laser Scanning Confocal Microscopes use laser beams (intense beams of light) to scan a specimen, which is usually tagged with a fluorescent dye.
2)
The laser causes the dye to fluoresce - give off light. This light is then focused through a pinhole onto a detector. The detector is hooked up to a computer, which generates an image. The image can be 3D.
3)
The pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.
4) They can be used to look at objects at different depths in thick specimens.
Electron microscopes use electrons instead of light to form an image.
They have a higher resolution than light microscopes so give more detailed images. There are two kinds of electron microscope:
1) Transmission electron microscope (TEM) - use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.
Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with. TEMs are good because they provide high resolution images (so they can be used to look at a range of organelles) but they can only be used on thin specimens.
A TEM image of a mitochondrion is shown above on the right.
Scanning electron microscope (SEM) - scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. The images produced show the surface of the specimen and can be 3D. But they give lower resolution images than TEMs. Here’s an SEM image of a mitochondrion.
magnification figures
light microscope-max resolution 0.2 um, max mag x1500
TEM-max resolution 0.0002, max mag can be more than x1000000(million)
SEM-max resolution-0.002um, max mag usually less than x500,000
