2A Cell Structure and Division Flashcards
What type of radiation does a light microscope use?
Light waves
What type of radiation does and electron microscope use?
Electrons
What is the wavelength of the light waves used in an electron microscope?
400-700nm
What is the wavelength of the electron beams used in an electron microscope?
0.005nm
What is the maximum magnification of a light microscope?
2000x
What is the maximum magnification of an electron microscope?
250 000x
What is resolution?
The degree to which it’s possible to distinguish between 2 objects that are very close together
What is the maximum resolution of a light microscope?
0.4-0.7μm
What is the maximum resolution of a transmission electron microscope?
0.5nm
What is the maximum resolution of a scanning electron microscope?
5-20nm
What’s the size of the smallest object you can see with a light microscope?
around 500nm
What’s the size of the smallest object you can see with a transmission electron microscope?
0.5nm
What’s the size of the smallest object you can see with a scanning electron microscope?
5-20nm
What type of lens is within a light microscope?
Glass
What type of lens is within a transmission electron microscope?
Electromagnetic
What type of lens is within a scanning electron microscope?
Electromagnetic
What kind of specimens (living or dead) can be looked at under a light microscope?
Either
What kind of specimens (living or dead) can be looked at under a transmission electron microscope?
Dead
What kind of specimens (living or dead) can be looked at under a scanning electron microscope?
Dead
What is the colour of the imaging in a light microscope?
Colour imaging
What is the colour of the imaging in a transmission electron microscope?
Black and white
What is the colour of the imaging in a scanning electron microscope?
Black and white
What is the cost of a light microscope?
£100s-£1000s
What is the cost of a transmission electron microscope?
£100 000s
What is the cost of a scanning electron microscope?
£100 000s
How does a light microscope work?
Light is passed through a thin specimen and convex lenses are used to manipulate how the light enters the eye
How does a transmission electron microscope work?
A beam of electrons that has been accelerated through an electromagnetic field is shot through a specimen and an image is formed off the interaction between the electrons and the sample
How does a scanning electron microscope work?
A beam of electrons is used to scan a sample and produce an image from what it finds
What are the advantages of a light microscope?
- can look at living material
- colour images
- cheaper
- easy to prepare
What are the advantages of electron microscopes?
- higher resolution
- higher magnification
What are the disadvantages of a light microscope?
- lower magnification
- lower resolution
What are the disadvantages of a transmission electron microscope?
- prep is difficult and time consuming
- expensive
- can only view dead specimens
What are the disadvantages of a scanning electron microscope?
- expensive
- large and must be stored away from electricity and any magnetism
- only dead specimens
- expensive
- prep is difficult and time consuming
- lower resolution than transmission electron microscope
What is the average diameter of an animal cell?
around 20μm
What is the average diameter of a plant cell?
around 40μm
What equation links magnification, image size and actual size?
image size = actual size x magnification
What resolution does a human eye have roughly?
100μm
How do you calibrate a microscope?
- use a micrometer to measure how wide a unit on the eyepiece graticule
- use this as a scale for samples when you measure them
Describe algae and how it resembles plant cells
- a type of protist
- can be unicellular (Chlorella) or multicellular (seaweed)
- have cellulose cell wall and chloroplasts so resemble plant cells
How are the chloroplasts in algae different to the ones in plants?
They are a different size and shape and in algae there may only be one chloroplast per cell
Give an example of algae that is often found growing in aquatic conditions
Spirulina
Where do algal blooms form and what can they cause?
In rivers and lakes they can cause disruption to natural ecosystems
Are fungi unicellular or multicellular? Give an example
They can be both
Unicellular eg. yeast
Multicellular eg. mushrooms
How do fungal cells differ from plant cells?
They are greatly similar however the cell wall in fungal cells is made from chitin and fungal cells don’t contain chloroplasts
What is the function of the cell-surface membrane?
- Controls what enters and leaves the cell
- Cell signalling
Describe the structure of the cell-surface membrane
- Primarily made of phospholipid and proteins
- Has receptor molecules on its surface (for cell signalling)
What is the function of the nucleus?
- Controls the activity of the cell
- Controls transcription in the cell
Describe the structure of the nucleus
- Surrounded by the nuclear envelope (full of pores)
- Contains chromosomes (each full of DNA) and one or more nucleolus
What is the function of the mitochondria?
- The site of aerobic respiration
- They produce ATP (an energy-carrying molecule found in cells of living things)
Describe the structure of the mitochondria
- Have a double membrane
- Inner membrane is folded inside the cell and forms extensions called cristae
- Between the cristae is the ‘cytoplasm’ of mitochondria called the matrix
What kind of cells have a high quantity of mitochondria and why?
- Cells with a high matabolic activity level
- eg. Muscle or epithelial cells
What is the function of the chloroplasts?
- Site of photosynthesis
Describe the structure of a chloroplast
Contains stroma, grana, thylakoids and intergranal lamellae.
What are the grana?
Stacks of up to 100 disc-like structures called thylakoids and where the 1st stage of photosynthesis takes place
What is the stroma?
A fluid filled matrix where 2nd stage of photosynthesis takes place
What is a thylakoid?
A disc-like structure in the chloroplast which contains the pigment for photosynthesis (chlorophyll) and some thylakoids have tubular extensions called intergranal lamellae which connect the disc stacks
How are the granal membranes in chloroplasts adapted to their function of harvesting sunlight and carrying out photosynthesis?
They provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes which carry out the first stage of photosynthesis
How is the fluid of the stroma in chloroplasts adapted to its function of harvesting sunlight and carrying out photosynthesis?
It possesses all the enzymes needed to make sugars in the second stage of photosynthesis
How are the chloroplasts adapted to their function of harvesting sunlight and carrying out photosynthesis? (not granal membranes or stroma fluid)
Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis
What are the two variations of the endoplasmic reticulum?
Rough and smooth
What is the endoplasmic reticulum’s structure as a whole?
It’s an elaborate, 3D system of sheet-like membranes spreading through the cytoplasm of cells. It’s also continuous with the outer nuclear membrane.
What do the membranes of the endoplasmic reticulum enclose?
A network of tubules and flattened sacs called cisternae
How are the smooth and rough endoplasmic reticulum structurally different?
The rough ER has ribosomes on its surface whereas the smooth one lacks these ribosomes and is more tubular in shape
What are the functions of the rough ER?
- Provide a large surface area for the synthesis of proteins and glycoproteins
- Provide a pathway for the transport of materials - especially proteins- throughout the cell
What are the functions of the smooth ER?
- Synthesise, store and transport lipids and carbohydrates
Which kind of cells may have a more extensive ER and why?
Cells in the liver or secretory cells eg. epithelial cells lining the large intestine
Because these cells store and manufacture a higher quantity of lipids, carbohydrates and proteins
What is the structure of the Golgi apparatus like?
It’s similar to the structure of the smooth ER but more compact. It consists of a stack of membranes that make up flattened sacs called cisternae with small rounded hollow structures called vesicles
What does the Golgii apparatus do?
The proteins and lipids made by the ER are passed through the Golgi in strict sequence and they are modified and often have non-protein components added to them eg. carbohydrates.
They are ‘labelled’ so they can be accurately sorted and sent to their correct destinations.
Once they’re sorted, the modified proteins and lipids are transported with Golgi vesicles which are regularly pinched off from the ends of the Golgi cisternae.
These vesicles move to the membrane of the cell, fuse with it and release their contents to the outside of the cell
What are the functions of the Golgi?
- add carbohydrates to proteins to form glycoproteins
- produce secretory enzymes such as those secreted by the pancreas
- secrete carbohydrates such as those used in making cell walls in plants
- transport, modify and store lipids
- form lysosomes
When are lysosomes formed and what do they contain?
When the vesicles produced by the Golgi contain enzymes such as proteases and lipases however they also contain lysozymes which are enzymes that are able to hydrolyse the cell wall of some bacteria
How many lysozymes may be contained in a lysosome?
Up to 50.
What is isolated by lysosomes?
Lysozyme enzymes are isolated from the rest of the cell by lysosomes before they are released to either outside of the cell or into a phagosytic vesicle within the cell
What are the functions of lysosomes?
- hydrolyse material ingested by phagosytic cells eg. white blood cells or bacteria
- release enzymes to the outside of the cell in order to destroy material around the cell
- digest worn out organelles so useful chemicals they are made of can be reused
- completely break down cells after they have died
What are ribosomes?
Small cytoplasmic granules found in all cells. They may occur in the cytoplasm or in the RER
What are the two types of ribosomes?
- 80s: found in eukaryotic cells and around 25nm in diameter
- 70s: found in prokaryotic cells, mitochondria and chloroplasts and is slightly smaller
What are the sub units of a ribosome?
There’s one large and one small and they each contain ribosomal DNA and protein
What is the function of a ribosome?
Protein synthesis
Describe the cell wall in plant cells
Consists of microfibrils of the polysaccharide cellulose which are embedded in a matrix. Cellulose microfibrils have considerable strength and therefore contribute to the overall strength of the cell wall
What is the middle lamella?
A thin layer which marks the boundary between adjacent cell walls and cements adjacent cells together
What are the functions of the cellulose cell wall?
- provide mechanical strength in order to prevent cell from bursting under the pressure created by osmotic entry of water
- gives mechanical strength to the plant as a whole
- allows water to pass along it and so contributes to the movement of water through the plant
What are the cell walls of algae made of?
Either cellulose or glycoprotein or a mixture of both
What are the cell walls of fungi made of?
A nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins
What is a vacuole?
A fluid-filled sac bounded by a single membrane. Within a mature plant cell there is usually one large central vacuole.
What is the membrane surrounding a vacuole called?
A tonoplast
What does a plant vacuole contain?
A solution of mineral salts, sugars, amino acids, wastes and sometimes pigments eg. anthocyanins
What are the functions of a vacuole?
- support herbaceous plants and herbaceous parts of woody plants by making cells turgid
- sugars and amino acids may act as a temporary food store
- pigments may colour petals to attract pollinating insects
How are eukaryotic and prokaryotic cells different?
- eukaryotic cells are larger and have a nucleus bound by nuclear membranes
- prokaryotic cells are smaller and have no nucleus or nuclear envelope
In a prokaryotic cell, what is the role of the cell wall?
- physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis
In a prokaryotic cell, what is the role of the capsule?
- protects bacterium from other cells and helps groups of bacteria to stick together for further protection
In a prokaryotic cell, what is the role of the cell-surface membrane?
- acts as a differentially permeable layer which controls the entry and exit of chemicals
In a prokaryotic cell, what is the role of the circular DNA?
- possesses the genetic information for the replication of bacterial cells
In a prokaryotic cell, what is the role of the plasmid?
- possesses the genes that may aid the survival of bacteria in adverse conditions eg. produces enzymes that break down antibiotics
What is the cell wall made of in prokaryotic cells?
murein (a polymer of polysaccharides and peptides)
How do prokaryotic cells further protect themselves other than having a cell wall?
They secrete a capsule of mucilaginous slime around the cell wall
How do bacteria store food reserves?
As glycogen granules and oil droplets
What are viruses?
Acellular, non-living particles. Smaller than bacteria.
What do viruses contain?
Nucleic acids such as DNA or RNA as genetic material but can only multiply inside a host cell
What is the nucleic acid within a virus enclosed in?
A protein coat called the capsid and some viruses are also enclosed by a lipid envelope. The lipid envelope (or capsid if this isn’t present) has attachment proteins which are essential for the virus to identify and attach to host cells
Why do cells need to constantly divide and how do they do this?
They are needed for growth and repair of tissues so they divide during the cell cycle
Which phase of the cell cycle to cells spend most of their time in?
Interphase: growing and copying DNA, three stages of interphase are G1, S and G2
G= growth
S= synthesis
What process do cells divide by? (eukaryotic and prokaryotic, not gametes)
Mitosis
What 4 letters help with order of mitosis?
PMAT
What is the first stage of mitosis?
Prophase
- chromosomes condense, they become shorter fatter and visible under microscope
- centrioles migrate to poles, small proteins that form a connective apparatus called the spindle
- nuclear envelope breaks down, results in free floating chromosomes in cytoplasm
What is the second stage of mitosis?
Metaphase (middle)
- chromosomes line up at the middle/equator of the cell
- chromosomes attach to the spindle by their centromeres, centromeres attach to the metaphase plate
What is the third stage of mitosis?
Anaphase (away)
- centromeres divide and separate sister chromatids
- the spindle contracts and pulls chromatids to the poles
- chromatids now appear v-shaped
What is the fourth stage of mitosis?
Telophase
- chromatids uncoil once they reach poles and become long and thin once more
- they are now referred to as chromosomes again
- nuclear envelope forms around the two sets of chromosomes to form two nuclei
What is the final stage of mitosis?
Cytokinesis (division)
- 2 genetically identical cells
How do you calculate the mitotic index of a sample of cells?
the number of cells dividing / total amount of cells
What is cancer caused by?
A mutation in a gene that controls cell division which causes cells to divide at an out of control rate
When does a tumour form?
When cells divide rapidly
What is an oncogene?
When a mutated gene is one that causes cancer
Are mutations common and do they all lead to cancer?
They are common and most don’t lead to cancer, most result in early cell death or the cell being destroyed by the immune system
What is cancer?
A tumour that invade surrounding tissue
What is the name for cancerous tumours and what is their shape?
Malignant, they are irregularly shaped
What do tumours require?
Space and energy
What is metastatic cancer?
Cancer that spreads
What are carcinogens?
Any agents that may cause cancer eg. UV light, tar in tobacco smoke, x-rays
What do metastatic malignant tumours do?
They interfere with the normal functioning of the organ/tissue eg. Blocking lungs
They can have parts break off and travel through the bloodstream or lymphatic system which forms secondary growths
What do most cancer treatments do?
- Most treatments disrupt the cell cycle and limit the rate of division
- Traditional cancer therapy also impacts healthy cells. It kills cancer cells more frequently as they constantly divide
What is chemotherapy?
Chemical therapy that stops production of enzymes required for cell division so cell can’t enter S phase
What is radiotherapy?
Ionising radiation that stops DNA replication, the DNA is checked for damage and kills itself if damage is detected
What is a p53 gene?
A gene that controls cell growth
What percentage of people with cancer possess a mutated p53 gene?
Almost 50%
How do most current cancer treatments/drugs work?
They control the rate of mitosis
Give two examples of cancer treatments/drugs and how they treat cancer.
Methotrexate- inhibits synthesis of DNA nucleotides in cells
Vincristine and taxol- prevent formation of mitotic spindle
What are oncoviruses?
Viruses that cause cancer (therefore known as carcinogens)
