B3 Cell Structure Flashcards
Function of nucleus
Site of DNA replication and transcription (making mRNA)
Contains genetic code for each cell
Structure of nucleus
Nuclear Envelope- double membrane
Nuclear Pores
Nucleoplasm - granular, jelly-like material
Chromosomes -protein-bound, linear
DNA
Nucleolus - smaller sphere inside which is the site of RNA production and makes ribosomes.
Function of endoplasmic reticulum
RER - Protein Synthesis
SER - Synthesis and store lipids and carbohydrates
Structure of endoplasmic reticulum
Rough and smooth ER have folded membranes called cisternae
Rough have ribosomes on cisternae
Function of Golgi apparatus and vesicles
Add carbohydrates to proteins to form glycoproteins
• Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
• Form lysosomes
Molecules are ‘labelled’ with their destination
Finished products are transported to cell surface in Golgi vesicles where they fuse with the membrane and the contents in released.
Structure of Golgi apparatus and vesicles
Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae
Function of lysosomes
Hydrolyse phagocytic cells
• Completely break down dead cells (autolysis)
• Exocytosis - release enzymes to outside of cell to destroy material
• Digest worn out organelles for reuse of materials
Structure of lysosomes
Bags of digestive enzymes - can contain 50 different enzymes.
Structure of mitochondria
Double membrane
Inner membrane called the cristae
Fluid centre called the mitochondrial matrix
Loop of mitochondria DNA
Function of mitochondria
• Site of aerobic respiration
Site of ATP production
• DNA to code for enzymes needed in respiration
Structure of ribosomes
Small, made up of two sub-units of protein and rRNA
80s- large ribosome found it eukaryotic cells (25nm)
70S - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.
Function of ribosomes
Site of protein synthesis
Structure of vacuole
Filled with fluid surrounded by a single membrane called a tonoplast
Function of vacuole
Make cells turgid and therefore provide support
• Temporary store of sugars and amino acids
• The pigments may colour petals to attract pollinators.
Function of chloroplasts
Site of photosynthesis
Structure of chloroplasts
Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled stroma contains enzymes for photosynthesis
Found in plants
Function of cell wall
Provide structural strength to cell
Structure of cell wall
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
Function of plasma membrane
Controls entrance and exit of molecules
Structure of plasma membrane
Found in all cells
Phospholipid bilayer - molecules embed within and attached on the outside (proteins, carbohydrates, cholesterol)
Calc mitotic index
Count how many cells are visible in filed of view and number of cells visible that are in stage of mitosis
Mitotic index = (number of cells in mitosis / total number of cells) x 100
What are the 4 stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Info about mitosis
1 round of division
Genetically identical cells are made
Diploid cells are made
Growth and repair
What happens in prophase
Chromosomes condense + become visible
Centrioles separate + move to opp ends of poles of cell
Nucleolus disappears
What happens in anaphase
Spindle fibres start to retract + pull centromere and chromatids they’re bound to towards opp poles
Centromere divide in 2
Individual chromatids are pulled to each opp pole (chromatids now referred to as chromosomes)
Requires energy in form of atp - provided by respiration in mitochondria
What happens in metaphase
Chromosomes align along equator
Spindle fibres released from poles now attach to centromere and chromatid
What happens in telophase
Chromosomes at each pole become longer + thinner again
Spindle fibres disintegrate, nucleus starts to reform
Nuclear membrane reforms
Nucleoli reappear
Cytoplasm splits in 2 to create 2 new genetically identical cells
What are the 3 stages of cell cycle
Interphase (G1, S, G2)
Nucelar division (mitosis + meiosis)
Cytokinesis
What is interphase
Longest stage in cell cycle
When organelles double, cell grows and DNA replicates
How do prokaryotic cells replicate
Binary fission and viruses don’t undergo cell division as they’re non-living
Viruses replicate inside of host cells they invade by injecting their nuclei acid into cell to replicate virus particles.
What are 3 types of microscopes
Optical (light) microscopes
Transmission electron microscopes
Scanning electron microscopes
Define magnification
how many times larger the image is compared to the object.
Define resolution
the minimum distant between two objects in which they can still be viewed as separate.
Optical (light) microscope
Light Beam condensed to create image
Poor resolution - light have longer wavelength
Low magnification
Coloured images
Can view living samples
Electron microscope (scanning or transmission)
Electron beam condensed to create image
Electromagnets used to condense beam
High resolution - electrons have short wavelength
High magnification
Black and white images
Sample must be in vacuum + non-living
Are small organelles visible in light microscope
No because of poor resolution of microscope - long wavelength of light
Why must Samples be in vacuum in Electron microscope
As Electrons are absorbed by air
Why must Samples be stained in Electron microscope
The image is in black and white
How is an image produced in TEM
Extremely thin specimen stained and place in vacuum
Electron gun produces electron beam that passes through specimen
Some parts absorb electrons and appear dark
Image produced is 2d - shows detailed images on internal structure of cells
How is an image produced in SEM
The specimens do not need to be thin, as the electrons are not transmitting through.
Instead, electrons beamed onto surface and electrons are scattered in diff ways depending on contours.
This produces a 3D image.
Magnification equation
Magnification = image size / actual size
Converting units
M - mm - micrometre - nm
——> x1000
<—— divide by 1000
What is cell fractionation used for
To isolate diff organelles so they can be studied
This enable individual organelle structures and functions to be studied
What happens in cell fractionation 1st
Cells are broken open to release contents and organelles are then separated
Why must cells be prepared in cold, isotonic, and buffered solution
Cold:
To reduce enzyme activity. When cell is broken open enzymes are released which could damage organelles
Isotonic:
organelles must be same water potential as solution to prevent osmosis, as this could cause organelles to shrivel / burst.
Buffered:
solution has pH buffer to prevent damage to organelles
What are the 2 main steps in cell fractionation
Step 1 = homogenisation
Step 2 = ultracentrifugation
What happens in step 1 of cell fractionation
cells must be broken open (homogenised) and this is done using blender.
cells are blended in cold, isotonic and buffered solution.
What happens in step 2 of cell fractionation
filtered solution is spun at high speed in centrifuge.
This separates organelles according to their density.
The order of organelle fractionation
1st : (slowest speed 1st)
Nuclei
Chloroplasts
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes
Last:(fastest speed)
How does the centrifuge separate the pellets
centrifuge spins at high speeds and centrifugal forces causes pellets of most dense organelle to form at bottom of tube.
process repeated at increasingly faster speeds, removing supernatant each time (liquid) leaving behind pellet ( isolated organelle).
supernatant is then spun again in centrifuge and process is repeated.
Suggest and explain the function of enzyme ATP hydrolase in absorbing amino acids.
1.Hydrolysing ATP into ADP + Pi releases energy
- This energy actively transports sodium ions out of the epithelial cells into the blood
- This creates a sodium ion concentration gradient from the ileum into the epithelial cells
- Sodium ions are cotransported into the epithelial cells with amino acids
(Mitosis practical) explain why the student used the 1st 5mm from onion root tip
This is where mitosis occurs
(Mitosis practical) explain why the student pressed down on the cover slip firmly
To create a single layer of cells so that light can pass through the specimen
(Mitosis practical) explain why the student added acid to the root
To break down links between cells/cell walls
Describe how HIV replicates inside of helper T cells.
- RNA is converted into DNA using the enzyme reverse transcriptase
- The DNA is inserted into the DNA of the helper T cell
- The DNA is transcribed into mRNA
- This HIV mRNA is then translated into HIV proteins to make a new viral particles
Function of the flagella in prokaryotic cell
Flagella rotates to enable bacteria to move
What is the capsule made of and its function
A slimy layer made of protein
This prevents the bacteria from desiccating (drying out) and protects the bacteria against the host’s immune system.
What are plasmids
small loops of DNA which only carry a few genes.
What is the cell wall like in prokaryotic cell
Contains murein (a glycoprotein)
What is the cell wall like in eukaryotic cell
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
Structure of nucleus in prokaryotic cell
No nucleus - Instead of a nucleus there is a single circular DNA molecule free in the cytoplasm which is not protein bound.
What don’t prokaryotic cells contain
Membrane bound organelles
E.g. mitochondria, chloroplasts, endoplasmic reticulum, Golgi, nucleus
What are the Key differences between prokaryotic cells and eukaryotic cells and what might prokaryotic cells also contain
The cells are much smaller.
No membrane bound-organelles
Smaller ribosomes
No nucleus
A cell wall made of murein
They may also contain:
Plasmids
A capsule around the cell
Flagella
