Cell Structure And Division Flashcards
What do plant cells have that animal cells don’t?
Cellulose cell wall
A permanent vacuole
Chloroplasts
Explain an algal cell and how they differ
Algae carry out photosynthesis but can be unicellular or multicellular.
Like a plant cell however the chloroplasts can be different size and shape to plant chloroplasts, some could have one big one.
Explain fungal cells and how they differ
Can be unicellular or multicellular
A lot like plant cells but have 2 key differences:
- Cell walls are made of chitin not cellulose
- Dont have chloroplasts
Describe and explain the function of the cell surface membrane
Mainly made of lipids and protein
Regulates movement of substances in and out of cell. It has receptor molecules on it, which allow it to respond to chemicals like hormones.
Describe and explain the function of the nucleus
A large organelle surrounded by a nuclear envelope which contains many pores.
The nucleus contains chromosomes and one or more structures called a nucleolus.
The nucleus controls the cells activates by controlling the transcription of DNA.
DNA contains instructions to make proteins.
The pores allow substances (ribosomes) to move between the nucleus and the cytoplasm.
The nucleolus makes ribosomes.
Describe and explain the function of the mitochondrion
Double membrane - inner is folded to form cristae
Inside is the matrix, which contains enzymes involved in respiration
The site of aerobic respiration
Aerobic respiration produces ATP
Mitochondria are found in large numbers in cells that are very active and require a lot of energy.
Describe and explain the function of the chloroplast
Found in plant and algal cells
Surrounded by a double membrane and also has membranes inside called thylakoid membranes
These membranes are stacked up in some parts to form grana
Grana are linked together by lamelle
Site of photosynthesis
Some happen in grana and some in stroma
Describe and explain the function of the golgi apparatus
A group of fluid filled membrane bound flattened sacs.
Vesicles are often at the edges of the sacs
It processes and packages new lipids and proteins.
It also makes lysosomes
Describe and explain the function of the golgi vesicle
Small fluid filled sac in the cytoplasm, surrounded by a membrane produced by the golgi apparatus
Stores lipids and proteins made by the golgi apparatus and transports them out of the cell
Describe and explain the function of the lysosome
A round organelle surrounded by a membrane, with no clear internal structure
Contains hydrolytic enzymes
They 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
Describe and explain the function of the ribosome
In cytoplasm or attached to RER
Made up of proteins and RNA
It is not surrounded by a membrane
Where proteins are made
Describe and explain the function of the rough endoplasmic reticulum
System of membranes enclosing a fluid filled space
The surface is covered in ribosomes
Folds and processes proteins that have been made by the ribosomes
Describe and explain the function of the smooth endoplasmic reticulum
Similar to RER but no ribosomes
Synthesises and processes lipids
Describe and explain the function of the cell wall
Rigid structure that surrounds cells in plants, algae and fungi
In plants and algae = cellulose
In fungi = chitin
Supports cells and prevents them from changing shape
Describe and explain the function of the cell vacuole (plants)
Membrane bound organelle found in cytoplasm
Contains cell sap - containing sugar and salts
The surrounding membrane is called the tonoplast
Helps to maintain pressure inside the cell and keep the cell rigid.
This stops the plants wilting.
Its also involved in the isolation of unwanted chemicals inside the cell
Explain how epithelial cells are specialised
In the small intestine and are adapted to absorb food efficiently
Walls have microvilli which increase SA for absorption
On the surface on their villi they have microvilli which increase SA even more
Also have a lot of mitochondria - to provide energy for the transport of digested food molecules into the cell
Explain how red blood cells are specialised
RBC are adapted to carry oxygen around the body. They have no nucleus to make more room for the oxygen carrying compound haemoglobin.
Explain how sperm cells are specialised
Contain a lot of mitochondria to provide the large amounts of energy they need to propel themselves towards an egg.
What is a prokaryotic cell structure and give an example?
Single celled organisms
Bacteria
Very small
Describe and explain the organelles in a prokaryotic cell
Cytoplasm = contains ribosomes
Flagellum = rotates to make the cell move
Free floating DNA = circular DNA as no nucleus
Plasmids = small loops of DNA that aren’t a part of the main circular DNA. Plasmids contain genes for things like antibiotic resistance and are not always present in prokaryotic cells.
Capsule = helps to protect the bacteria from attack by cells of the immune system
Cell wall = supports and prevents changing shape = made of murein (glycoprotein)
Cell surface membrane = controls the movement of substances in and out of the cell
How do prokaryotes replicate - explain the process?
Process = binary fission
Step 1
- The circular DNA and plasmids replicate. The main DNA loop is only replicated once, but the plasmids can be replicated loads of times
Step 2
- The cell gets bigger and the DNA loops moves to opposite poles of the cell
Step 3
- The cytoplasm begins to divide and the new cell wall begins to form
Step 4
- The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA but can have variable number of copies of the plasmids
Explain and give an example of a virus
Viruses are acellular - they are not cells
Viruses are just nucleic acids surrounded by protein
Examples include HIV and influenza
All viruses invade and reproduce inside the cells of other organisms - these are known as host cells
What organelles do viruses have?
- Protein coat = capsid
- Core of genetic material = RNA or DNA
- Attachment proteins which let the virus attach to a suitable host cell
- Reverse transcriptase
How do viruses replicate?
Don’t undergo cell division
They need to inject their DNA or RNA by attaching to the host cell surface = they do this by using their attachment proteins to bind to complimentary receptor proteins on the cell surface membrane of the host cells.
- Virus attached to host cell receptor proteins
- Genetic material is released into the host cell
- Genetic material and proteins are replicated by host cell
- Viral components assemble
- Replicated viruses released from host cell
What is the lytic cycle?
Virus attaches to host cell
Inject DNA or RNA
Cell follows instructions - making copies
Causes cell membrane to rupture and virus goes to effect other cells
What is the lysogenic cycle?
Bacteriophage (goes after bacteria)
Inject genetic material
Stays hidden in cells DNA
Cell reproduces with virus in it
Give the equation for magnification
Magnification = Size of image / Size of real object
How to convert milimetre to micrometre ?
x 1000
How to convert micrometre to nanometre?
x 1000
Define resolution
Resolution is how detailed the image is
How well a microscope can distinguish between between 2 points that are close together.
Explain optical (light) microscopes
Use light to form an image
Max resolution of 0.2 micrometres
Cannot see ribosomes, ER and lysosomes
Maximum useful magnification is around x1500
Explain electron microscopes
Use electrons to form an image
Higer resolution so can give a more detailed image.
Max resolution of 0.0002 micrometres
Max useful magnification is around x 1500000
Produce black and white images that are often coloured by a computer
Explain transmission electron microscopes (TEMs)
TEMs us electromagnets to focus a beam of electrons which is transmitted through the specimen. Denser parts absorb more electrons, which makes them look darker on the image.
Give high resolution images so you can see the internal structures of organelles but you have to view the specimen in a vacuum .
Specimen has to be dead and thin
Explain scanning electron microscopes (SEMs)
SEMs 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 you see show the surface of the specimen and they can be 3D.
SEMs are good as can be used on thick specimens but give lower resolution images than TEMs. Has to be non living
How to prepare microscope slides for an optical microscope?
- Start by pipetting a small drop of water onto the centre of the slide
- Then use tweezers to place a small thin section of your specimen on top of the water drop
- Add a drop of stain
- Add the cover slip - lower it on an angle to avoid air bubbles
Cell fractionation is separating organelles from the rest of the cell
Explain the first stage
Homogenisation
Can be done in different ways - vibrating the cells or grinding up to break the plasma. membrane and release the organelles into solution
The solution must be ice cold to reduce enzyme activity
The solution should also be isotonic - to prevent osmosis
A buffer solution should be added to maintain pH
Cell fractionation is separating organelles from the rest of the cell
Explain the first stage
Filtration
The homogenised cell solution is filtered through gauze to separate any large cell debris or tissue debris.
The organelles are smaller than the debris so they pass through the gauze.
Cell fractionation is separating organelles from the rest of the cell
Explain the first stage
Ultracentrifugation
- The cell fragments are poured into a tube. The tube is put into a centrifuge and is spun at low speed. The organelles that are heaviest settle at the bottom forming a thick sediment - the pellet. The rest of the organelles are suspended in the solution - the supernatant
- The supernatant is drained off, poured into another tube and spun again at a higher speed.
- The process continues at higher speeds until all organelles are separated out
Give the order that organelles are normally separated during cell fractionation
Nuclei
Chloroplasts
Mitochondria
Lysosomes
ER
Ribosomes
What happens during interphase?
Gap phase 1 = cell grows and new organelles and proteins are made
Synthesis = cell replicates its DNA, ready to divide by mitosis
Gap phase 2 = cell checks for error and makes any needed repair. Keeps growing and proteins needed for cell division are made
ATP content is increased
Explain the structure of a chromosomes
Chromosomes are made of 2 strands joined in the middle by a centromere.
The separate stands are called chromatids.
Two strands on the same chromosome are called sister chromatids
Explain prophase
The chromosomes condense, getting shorter and fatter.
Tiny bundles of centrioles begin moving to opposite ends of the cell, forming a network of spindle fibres.
The nuclear envelope breaks down and chromosomes lie free in the cytoplasm.
Explain metaphase
The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere
Explain anaphase
The centromeres divide, separating each pair of sister chromatids. The spindles contract pulling the chromatids to opposite poles of the spindle, centromere first. This makes the chromatids appear v shaped.
Explain telophase
The chromatids reach the opposite poles on the spindle.
The uncoil and become long and thin again.
They are now called chromosomes again.
A nuclear envelope forms around each group of chromosomes so there are now 2 nuclei
Division of the cytoplasm (cytokinesis) finishes.
There are now 2 daughter cells that are genetically identical to each other.
How does cancer occur?
If there is a mutation in the gene that controls cell division, the cells can grow out of control/ The cells keep on dividing to make a tumour.
Cancer is a tumour that invaded surrounding tissue.
Explain how chemotherapy can be used to treat cancer
Prevents the synthesis of enzymes needed for DNA replication.
If these aren’t produced, the cell is unable to enter the synthesis phase, disrupting the cell cycle and forcing the cell to kill itself.
Explain how radiation can be used to treat cancer
Radiation can damage DNA
At several points in the cell cycle the DNA in the cell is checked for damage.
If severe DNA damage is detected the cell will kill itself
LOOK AT PAGE 90 FOR REQUIRED PRACTICAL
How to calculate mitotic index?
number of cells with visible chromosomes / total number of cells observed
