Chapter 3 - Cell structure Flashcards
What is an object?
The material placed under the microscope
What is an image?
The appearance of the material viewed under the microscope
Why is the resolution of an electron microscope greater than that of an optical microscope?
Electrons have a very small wavelength compared to light
Equation for magnification
Magnification = size of image/size of real object
What is magnification?
How much bigger the image is than the specimen you’re looking at
What is resolution?
How well a microscope can distinguish between two points that are close together
What do optical microscopes use to form an image?
Light
What do electron microscopes use to form an image?
Electrons
Maximum resolution of a light microscope
0.2 micrometres
Maximum magnification of a light microscope
1500 x
Maximum resolution of electron microscopes
0.0002 micrometres
Maximum magnifiation of electron microscopes
1,500,000 x
What are the two types of electron microscope?
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
How do transmission electron microscopes work?
A beam of electrons is focussed onto a specimen using electromagnets. The electrons are transmitted THROUGH the specimen. Denser parts of the specimen absorb more electrons, so they appear darker
What are the main limitations of the TEM? (3)
They can only be used on thin specimens
The whole system must be observed in a vacuum - living specimens can’t be viewed
A complex preparation process means artefacts are common
What are artefacts?
Things that you can see on the microscope but aren’t part of your specimen
How many micrometres are in a millimetre?
1,000
How many nanometres are in a micrometre?
1,000
How do scanning electron microscopes work?
A beam of electrons is scanned onto the surface of a specimen. This knocks electrons off of the specimen which are gathered in a cathode ray tube to form an image
Advantages of TEM
High resolution images mean you can see internal structures like chloroplasts
Advantages of SEM
They can be used on thick, and living, specimens
Disadvantages of SEM
The resolution is lower than TEM
What is an eyepiece graticule?
A transparent ruler with numbers but no units
How to calibrate a microscope?
1) Divide total length of stage micrometre by how many intervals to find one micrometre unit
2) Find a point where the two lines are equal
3) Work out how many micrometre units equal how many eyepiece units
4) Convert the stage micrometre units to micrometres
5) Divide stage micrometre units by eyepiece units to find the value of one eyepiece unit
6) This can be used in calculations
What is cell fractionation?
The process where cells are broken up and different organelles they contain are separated out
During homogenisation, why is the solution:
a) cold?
b) the same water potential as the tissue?
c) buffered?
a) to reduce enzyme aactivity that could break down organelles
b) to prevent organelles bursting or shrivelling due to osmosis
c) any change in pH could affect the organelles or enzymes
What happens during homogenisation?
Cells are broken up in a blender to release organelles
What happens during filtration?
The homogenate is filtered to remove any large sections of cells and debris
What happens during ultracentrifugation?
The filtrate is poured into a test tube, placed in the centrifuge and spun slowly
The heaviest organelles sink to the bottom, forming the pellet, whilst the rest of the organelles stay suspended in a fluid called the supernatant
The supernatant is drained off, poured into another test tube and spun at a higher speed
The next heaviest organelles form the pellet and are removed
The process repeats until the desired organelle forms the pellet, which can then be studied
*Description of the nucleus
A large organelle, which is surrounded by the nuclear envelope (a double membrane), covered in pores to allow mRNA to leave. Inside the nucleus is nucleoplasm and in this are chromosomes, containing DNA. One or more nucleoli can also be found her, which are used for making ribosomes.
*Function of the nucleus
The nucleus controls the activities of the cell by controlling the transcription of DNA
*Description of mitochondria
Mitochondria have a double membrane, the innermost of which is folded to form structures called cristae. Surrounding these cristae is a matrix
*Function of cristae
Large surface area for aerobic respiration
*Function of matrix
Contains enzymes involved in respiration
*Function of mitochondria
The site of aerobic respiration, which produces ATP
*Description of cell surface membrane
The membrane found on the surface of animal cells
*Function of cell surface membrane
Controls what enters and leaves cell
*Rough size of mitochondria
Between 2 and 10 um
*What is the chloroplast envelope?
A double membrane surrounding the organelle
*What are grana?
Stacks of thylakoid membranes inside chloroplasts
*What is the stroma?
A matrix where the sugars are synthesised during photosynthesis
*Function of chloroplasts
Site of photosynthesis
*How are chloroplasts adapted for photosynthesis?
The grana provide a large surface area for the first stage of photosynthesis
Chloroplasts contain ribosomes and DNA so they can quickly make proteins required for photosynthesis
What are the two types of endoplasmic reticulum?
Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (SER)
What is the RER?
A system of membranes covered in ribosomes
Functions of the RER
Provide a pathway for proteins to move throughout the cell
Provide a large area for protein synthesis
Functions of the SER
Synthesise, store and transport lipids and carbohydrates
What are cisternae?
A stack of membranes that make flattened sacks
Functions of Golgi apparatus
Processes and packages new lipids and proteins
Form lysosomes
Functions of Golgi apparatus
Processes and packages lipids and proteins
What are Golgi vesicles?
Fluid-filled sacks produced by the Golgi apparatus
Function of Golgi vesicles
Stores lipids and proteins made by the Golgi apparatus and transports them out of the cell
When are lysosomes formed?
When vesicles contains enzymes like lipases and proteases
What are lysozymes?
Enzymes found in lysosomes which hydrolyse the cell walls of certain bacteria
Functions of lysosomes
Digest worn-out organelles and cells after they have died
Hydrolyse bacteria cells during phagocytosis
What are the two types of ribosome?
80S - found in eukaryotic cells, relatively big
70S - found in prokaryotic cells, mitochondria and chloroplasts, smaller
Description of ribosomes
A very small organelle, made of proteins and RNA
Function of ribosomes
Protein synthesis
Function of microvilli
Increase surface area for absorption
*What is a cell wall?
A rigid structure surrounding cells in plants, algae and fungi. It consists of cellulose embedded in a matrix
*Functions of the cell wall
To prevent the cell bursting from the movement of water
Gives mechanical support to the cell
*What are cell walls made from in fungi?
Chitin
*What is the tonoplast?
The membrane surrounding the vacuole
*What is a vacuole?
A fluid filled sack surrounded by the tonoplast
*Function of a vacuole
Stores water to maintain water and keep the cell rigid and the plant turgid
Helps to isolate unwanted chemicals
Why do cells become specialised?
To carry out specific functions
How do cells become specialised?
Certain genes can be turned on and off
What is a tissue?
A group of cells working together to perform a specific function
Function of the epithelial tissue
Covers the inside and outside of organs
Function of xylem
Transports water and mineral ions throughout the cell and also gives mechanical support
What is an organ?
A variety of tissues coordinated to perform a variety of functions
What does muscular tissue do in the stomach?
Churns contents
What does epithelial tissue do in the stomach?
Protects stomach lining
Which of the blood vessels are organs and which are tissues?
Organs: arteries and veins
Tissue: capillaries
Function of phloem
Moves food away from the leaves in a plant
Function of the epidermis in a plant
To protect the leaf
Function of the spongy mesophyll in a plant
Gaseous diffusion
Function of the palisade mesophyll in a plant
Photosynthesis
What does the digestive system do?
Digests and processes food
What does the respiratory system do?
Breathing and gas exchange
What does the circulatory system do?
Pumps and circulates blood
*What are cell walls made from in bacteria?
The glycoprotein murein
Function of slime capsule
Protects bacterium from other cells and helps them group together
Which ribosomes are found in bacteria cells?
70S
*Function of circular DNA
Contains information needed for bacteria cells to replicate
*Function of plasmid
Contains genes that may help the bacteria survive in adverse conditions
*Is the DNA of bacteria cells associated with proteins?
No
Why are viruses described as acellular?
They are nucleic acids surrounded by a protein called the capsid - they aren’t alive
What is the function of attachment proteins and where are they found?
They are found sticking out from around the capsid and help virus cling to a host cell
How do viruses replicate?
They use proteins to attach to host cells
They inject their DNA into the host cell, which makes the cell replicate the viral particles
Why can viruses only infect one type of cell?
Their attachment proteins are complementary to just one receptor cell
Process of binary fission
The DNA and plasmids in the cell replicate
The cell gets bigger and the DNA moves to opposite ends of the cell, where it attaches to the membrane
The cytoplasm begins to divide and new cell walls begin to form
A new cell wall forms between the two molecules of DNA, creating two identical daughter cells
*What is mitosis?
A parent cell divides to produce two genetically identical daughter cells
*3 uses of mitosis?
Growth, repair and reproduction
*What are the three stages in the cell cycle?
Interphase
Nuclear division
Cytokinesis
*Which stage isn’t part of mitosis?
Interphase
*How to remember the stages of the cell cycle?
IPMAT
*What happens during interphase? 2
The cell’s DNA unravels and replicates
The organelles and ATP are replicated
*What happens during prophase? 3
The chromosomes condense and become visible
Centrioles move to opposite ends of the cell, forming the spindle apparatus
The nuclear envelope breaks down
*What happens in metaphase? 2
The chromosomes line up along the cell’s equator
The spindle fibres attach to the centromere
*What happens in anaphase? 2
The centromeres divide, separating the chromatids. The spindles contract and pull chromatids to the cell’s poles
*What happens during telophase? 2
The chromosomes reach the poles and unravel
The cytoplasm divides and two nuclear envelopes form, leaving two identical daughter cells
*What is cytokinesis?
The process by which the cytoplasm divides
What is cancer?
A group of diseases characterised by a growing disorder of cells
Characteristics of benign tumours
Grow slowly, are more compact and less life threatening
Characteristics of malignant tumours
Grow quickly, less compact and are more life threatening
How do cancer drugs work?
They disrupt the cell cycle to stop the tumour dividing and growing
How does chemotherapy work?
Chemicals prevent the synthesis of enzymes needed for DNA replication
How does radiotherapy work?
Radiation damages DNA so the cell kills itself
Formula for mitotic index
Number of cells with visible chromosomes/ total number of cells observed
Why are hair cells often affected by cancer drugs?
The drugs target cells that divide rapidly, such as hair cells
Why do specimens have to be kept in a vacuum before using an electron microscope?
The air would otherwise absorb the electrons and prevent them reaching the specimen
*What chromosomes do women have?
XX
*What chromosomes do men have?
XY
