Paper 1 and 3: Cells Flashcards
What is the function of the nucleus? [2]:
- contains the genetic material of the cell
- controls the activity of the cell
Nucleus location:
It is surrounded by a nuclear envelope which contains nuclear pores and chromosomes
Inside the nucleus [2]:
- Chromatin
- The nucleolus
Chromatin [definition]:
DNA wrapped around proteins called histones
What is the nucleolus?
The site where ribosomes are made
What are ribosomes and where are they found? [2]:
- Ribosomes are the site of protein synthesis
- They are found floating in the cytoplasm or attached to the RER
Cytoplasm [definition]:
A watery liquid where most chemical reactions occur
What does RER stand for?
Rough endoplasmic reticulum
What is the rough endoplasmic reticulum?
A membrane enclosed, fluid filled, space covered with ribosomes.
What is the function of the RER?
It is the site where proteins are processed and folded
Eukaryotic ribosomes =
80S- bigger than prokaryotic ribosomes
Prokaryotic ribosomes =
70S- smaller than eukaryotic ribosomes
What does SER stand for?
Smoothe endoplasmic reticulum
SER [definition]:
Membrane enclosed, fluid filled spaces that are NOT covered with ribosomes
SER [function]:
It synthesises and processes lipids
Golgi aparatus/body [definition]:
A group of fluid filled, flattened sacs, associated with vesicles
Vesicle [defintion]:
Small, membrane bound sacs
Golgi apparatus [function]:
It processes and packages new lipids and proteins which are then transported else where in the cell by the vesicles
Lysosomes [definition]:
Rounded organelles surrounded by a double membrane.
Lysosomes [function]:
They contain digestive enzymes called lysozymes which are used to digest pathogens and worn/damaged components of the cell
Mitochondria [description]
[2]:
- It has a double membrane where the inner membrane folds into cristae
- It contains a matrix similar to cytoplasm, and enzymes that are involved in respiration
Mitochondria [function]:
It is the site of aerobic respiration and therefore the production of ATP. It is the energy source of the cell
Cell/ surface membrane [function]:
Controls the movement of substances into and out of the cell
Microvilli [definition]:
Folds on the cell membrane
Microvilli [function]:
Increase surface area. Mostly found on cells that are involved in absorption
Thingies found in a chloroplast [6]:
- Thylakoid/ Granum
- Double membranes (outer + inner)
- Lamellae
- Stroma
- Lipid droplets
- Starch granules
TDLSYLS
What is a granum?
A stack of thylakoids
What is the function of the lamallae?
It conects granum
Eukaryotic cells [info]
[3]:
- Has a nucleus
- Has membrane bound organelles
- 80S ribosomes
Prokaryotic cells [info]
[5]:
- Does NOT have a nucleus
- Does NOT have any membrane bound organelles
- Has plasmid loops of DNA instead
- 70S ribosomes
- Can have slime capsules
Plasmids:
Small loops of DNA that carry a few genes (usually coding for antibiotic resistance)
Flagellum:
Helps in locomotion. There can be more than one in a cell
Slime capsule:
Acts as protection for the bacteria from the immune system
Pilli:
Allow plasmids to go through one bacteria into the next
Animal cells do not have [3]:
- Cell walls
- Chloroplasts
- Vacuoles
Plant cell walls are made of…
cellulose
Algal cell walls are made of…
cellulose
Fungal cell walls are made of…
Chitin
What are the 3 different types of microscopes used to study cell structure?
- The light/optical microscope
- The scanning electron microscope (SEM)
- The transmission electron microscope (TEM)
The light microscope [3]:
- Use light to form an image
- Has the lowest magnification and resolution
- Has a maximum magnification of x1500
Why do specimens for a light microscope need to be stained?
The stain provides a greater contrast which allows us to see in more detail
Why do light microscope specimens have to be thin?
So that light can pass through
Why do light microscopes have the lowest resolution?
cus visible light has a long wave length
The scanning electron microscope (SER)
[4]:
- Allows you to see in 3D/ produces 3D images
- Can be used on thick specimens
- Has a lower resolution than TER but higher than light microscope
- Cannot be used on living specimens
How do scanning electron microscopes work? [3]:
- The image is produced when a beam of electrons is scanned across the specimen.
- This knocks electrons off the specimen
- The electrons are collected in a cathode ray to form an image
Transmission electron microscopes (TEM)
[4]:
- Gives the highest resolution
- Cannot be used on living specimens
- Specimens must be thin
- Allows internal structures in a cell to be seen in detail
How do TEM microscopes work? [2]:
- Uses electromagnets to focus a beam of electrons which is transmitted through the specimen
- The denser parts of the specimen absorb more elctrons which makes them look darker
Artefacts:
Debris floating around in a cell
Resolution vs magnification [2]:
- Resolution= how clear the image is
- Magnification= how zoomed in it is lol
Image size =
magnification x actual size
mm → μm =
x 1000
μm → mm
÷ 1000
How to make a slide [3]:
- Place a drop of water on the slide (to wash it)
- Place a thin specimen on the slide and apply a stain
- Place a cover slip over the specimen at 45 º using a mounted needle
Obtaining organelles from cells/ Cell fractionation [7]:
- Tissue put in ice cold isotonic solution containing a buffer
- Tissue is homogenised using a homogeniser or blender
- Homogenised cell solution is filtered to remove large cell debris
- Cell solution is poured into a centrifuge tube to go through ultracentrifugation
- A pellet of the heaviest organelles forms at the bottom of the tube
- The liquid above the pellet (supernatant) contains the lighter organelles and is drained into a different tube
- Process repeated at higher speeds until all the organelles are separated out
Why is the tissue homogenised?
To beak up the cell membrane of the tissue cells, releasing the organelles into the solution
Why are the tissues placed in an ice cold solution?
To slow down enzyme activity so that the organelles are not damaged
Why is the solution buffered?
Buffers maintain the pH of a solution so that proteins are not denatured and that organelles are not damaged
Why are the tissues placed in an isotonic solution?
To prevent osmosis and water entering the organelles, causing them to burst
In what order do the organelles sediment out? [5]:
- Nucleus
- Mitochondria + chloroplasts
- Lysosomes
- SER + RER
- Ribosomes
NMLSER
What are the 4 stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
Cell cycle [4]:
- Mitosis
- Gap phase (G1)
- Synthesis (s/ DNA replication)
- Gap phase (G2)
Common parts of prokaryotic cells [3]:
- plasmid(s)
- Capsule surrounding the cell
- One or more flagella
Viruses [4]:
- Are acellular and non-living
- Have genetic material,
- capsid,
- attachment protein
What are the stages of mitosis? [4]:
- Prophase
- Metaphase
- Anaphase
- Telophase (&and cytokinesis)
Prophase [3]:
- The nuclear envelope breaks down
- Chromosomes condense, shorten and fatten
- Centrioles move to opposite poles to form spindle fibres
Metaphase [3]:
- The chromosomes are seen to be made out of two chromatids
- Spindle fibres attach to the centromere of the chromosomes
- Chromosomes line up along the equator
What is the order of the stages in mitosis?
PMAT
Anaphase [2]:
- Spindle fibres contract to pull sister chromatids to opposite poles of the cell
- Sister fibres look v-shaped
Telophase [4]:
- Sister chromatids at opposite poles of the cell
- The nuclear envelope reforms around the chromosomes
- The are 2 nuclei now
- The cytoplasm splits and there are now 2 genetically identical daughter cells
What is cytokinesis?
When the cytoplasm splits
What is the process in which prokaryotic cells divide?
Binary fission
Binary fission [4]:
- The circular DNA molecule replicates and both copies attach to the cell membrane
- Plasmid replicates
- The cell membrane begins to grow between the 2 DNA molecules, dividing the cytoplasm in 2
- A new cell wall forms between the 2 molecules of DNA, dividing the original cell into 2 identical daughter cells
What does each daughter cell have in binary fission? [2]:
- A copy of circular DNA
- variable number of copies of plasmids
Virus cell division [2]:
- They do not undergo cell division
- Following the injection of their nucleic acid, the infected host cell replicates the virus particles
Required practical 2
Preparation of stained, squashed cells from plant root tips; set up and use an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index
Why is the tip of the root cell used in required practical 2?
It is where the most meristematic tissue can be found
lots of meristem tissue
Mitotic index =
Number if cells in mitosis
————————————- x 100
Total number of cells
Interphase [2]:
- Occupies the most of the cell cycle (G1 & G2)
- Also known as the resting stage because no division takes place
Nuclear division:
Mitosis or meiosis
Mitosis is a…
controlled process
What does uncontrolled cell division lead to?
Tumours/ cancer
Cancer treatments [2]:
- Preventing the DNA from replicating
- Inhibiting the metaphase stage of mitosis by interfering with spindle formation
Issue with cancer treatment drugs [2]:
- They also disrupt the cell cycle of normal cells and not just cancerous ones
- However the drugs are very effective against rapidly dividing cells
Cell surface membrane [2]:
The plasma membrane that surrounds the cell and forms the boundary between the cell cytoplasm and the environment
- Allows substances in and out of the cell
Why is it called the fluid mosaic model? [2]:
- Mosaic- because proteins of different shapes and sizes are embedded within the phospholipid bilayer
- Fluid- because it can move and is flexible. It is not rigid.
Cell membrane components [7]:
- Phospholipid Bilayer
- Extrinsic Proteins
- Carrier Proteins
- Protein channels/ Channel protein
- Glycoproteins
- Glycolipids
- Cholesterol
Phospholipid Bilayer [3]:
- This forms a double layer and is the main part of the membrane
- It forms a barrier between the internal and external environment.
- It prevents water soluble molecules from entering the cell.
Carrier Proteins [function]:
These proteins allow large molecules to enter and leave the cell by changing shape
Protein channels/ Channel protein [2]:
- These proteins have smaller water filled pores running through the middle
- They allow some large molecules, water soluble and charged molecules to enter and leave the cell
Extrinsic Proteins [function]:
These are proteins that are partly embedded in the phospholipid bilayer and provide mechanical support
Glycoproteins [2]:
- They are protein molecules embedded in the phospholipid bilayer with a carbohydrate molecule attached
- Their function is as receptors and they are also involved in cell recognition
Cholesterol molecule [function]:
These molecules are randomly found throughout the phospholipid bilayer, adding strength and rigidity
Glycolipids [2]:
- These are phospholipid molecules in the bilayer with a carbohydrate chain attached
- Its function is also reception and recognition
What is a thylakoid?
Flattened sacs inside a chloroplast, bound by pigmented membranes where photosynthesis take place
What happens during interphase that prepares cells for mitosis? [3]:
- Build-up of energy stores
- Increase in cytoplasm
- Synthesis of proteins
