3 - Cell Structure Flashcards
What is the resolution of a microscope?
The minimum distance apart two objects can be in order to appear as separate items.
How many micrometers are in a millimetre?
1000
What many Nanometers are in a micrometer?
1000
What is the purpose of cell fractionation?
To isolate organelles for further study.
What conditions must the cell fractionation solution be in?
Cold - reduce enzyme activity that could break down the organelles
Isotonic (same water potential as tissue) - prevents bursting or shrinking organelles
Buffered - stops pH alteration which could alter structure of organelles
What are the two stages of cell fractionation?
Homogenation
Ultracentrifugation
Explain homogenation?
Cells are broken up by a homogeniser, releasing the organelles from the cell. The homogenate (resultant fluid) is then filtered to remove any debris and complete cells.
Describe the process of ultracentrifugation.
Tube of filtrate placed in centrifuge, spun at slow speed.
Heaviest organelles forced to bottom of tube to form a sediment.
Supernatant (fluid at the top) removed leaving sediment.
Supernatant transferred and spun faster, forcing the next heaviest organelles to the bottom.
Process repeats until desired organelle becomes sediment and is able to be separated.
What are the two types of electron microscopes?
Transmission Electron Microscope
Scanning Electron Microscope
What are four limitations of a TEM?
The system must be a vacuum, therefore no living organisms
Complex staining process, still no colour
Specimen must be extremely thin, in order for electrons to pass through, giving a 2D image
Image may contain artefacts
How can you tell the difference between a TEM and SEM image?
SEM gives a 3D image, but slightly less resolution.
Why are electron microscopes favourable compared to their optical counterparts?
Electrons have a shorter wavelength than light, therefore high resolving power.
What is the function of a nucleus in a eukaryotic cell?
Contains hereditary information, and controls cell’s activities
How large is the average nucleus?
10-20 um
What is the function of the nuclear envelope/membrane?
It is a double membrane that controls the entry and exit of materials in and out of the cell, and contain the reactions within.
Give 5 elements of the nucleus.
Nuclear envelope
Nuclear pores
Nucleoplasm
Chromosomes
Nucleolus
What is the function of the nucleolus?
Retain genetic information of cell (chromosomes)
Manufacture ribosomes and ribosomal RNA
Act as control centre of cell through production of mRNA and tRNA
What is the matrix of a mitochondrion?
Contains proteins, lipids, ribosomes and DNA that allows mitochondria to control production of proteins.
Many enzymes for respiration are found in the matrix.
What is the purpose of the mitochondria?
Production of ATP. This means metabolically active cells contain many mitochondria, ie muscle and epithelial cells.
What is a granum?
A stack of thylakoids within a chloroplast.
What is the purpose of the stroma?
It is the site of the light independent stage of photosynthesis (synthesis of sugars).
Give three ways in which chloroplasts are adapted for their function.
The granal membranes provide a large surface area for the first stage of photosynthesis.
The fluid in the stroma contains enzymes needed for the second stage of photosynthesis.
Chloroplasts contain both DNA and ribosomes to quickly and easily manufacture proteins necessary for photosynthesis.
What are the flattened sacs on the endoplasmic reticulum called?
Cisternae
What is the role of the smooth endoplasmic reticulum?
Synthesis, storing and transport of lipids and carbohydrates.
What is the role of the rough endoplasmic reticulum?
Provide surface area for the synthesis of proteins/glycoproteins
Provide a pathway for the transport of proteins throughout the cell
What is the difference between the rough and smooth ER?
Rough ER has ribosomes on its surface, smooth ER does not.
What are the name of the sacs that leave the Golgi body?
Golgi vesicles
What are the five roles of the Golgi apparatus?
Add carbohydrates to proteins to form glycoproteins.
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes
How is a lysosome formed?
When a vesicle produced by the Golgi body contains enzymes such as lysozymes, proteases and lipases.
What types of cells are lysosomes notably prominent in?
Secretory cells (ie epithelial) and phagocytic cells.
What are the four functions of lysosomes?
Hydrolyse pathogenic material ingested by phagocytic cells
Release enzymes to the outside of the cell (exocytosis)
Digest worn out organelles to reuse useful chemicals
Completely break down dead cells (autolysis)
What is the function of ribosomes?
They are the site of protein synthesis.
Explain the structure of a ribosome.
Ribosomes are made from two subunits: one large and one small. Each contains ribosomal RNA and protein.
How large are ribosomes in eukaryotic cells?
80S
What is the middle lamella?
Marks the boundary between adjacent cell walls, and cements them together.
What are fungi cell walls made from?
Chitin
What are two functions of the cell wall?
Provide mechanical strength to individual cells to stop them bursting
Provide mechanical strength to the plant as a whole
What is the single membrane which surrounds the vacuole?
Tonoplast.
What do plant vacuoles always contain?
Mineral salts, sugars, amino acids and wastes.
What are two functions of vacuoles?
Sugars and amino acids can act as a temporary food source
Support plants by making cells turgid
What is a tissue?
A group of similar cells working together to carry out a specific function
What are three examples of tissues?
Epithelial tissue (sheets of epithelial cells)
Xylem
Muscle tissue
What is an organ?
A group of tissues coordinates to perform a variety of functions, including one major one.
Give two examples of organs.
Stomach
Leaf
What is an organ system?
Organs working together as a single unit. They can be grouped together to carry out functions like efficiently.
Give two examples of organ systems within humans.
Digestive system
Circulatory system
What is a bacterial cell wall made from?
Murein
How is DNA stored in prokaryotic cells?
Circular strands of DNA
Plasmids
What is the role of a capsule? (2)
Protects the bacterium from other cells
Helps groups of bacteria stick together for further protection
What is the difference in association of DNA in eurkaryotic and prokaryotic cells?
In eurkaryotic cells, DNA is associated with proteins called histones. In prokaryotic cells, DNA is not associated with any proteins.
What encloses the nucleic acid in a virus?
A capsid
What are attachment proteins?
Essential proteins on the capsid or lipid envelope of a virus. They allow viruses to identify and attach to a host cell.
Are the cells produced in mitosis haploid or diploid?
Diploid
How many cells are produced in mitosis?
2
What are the four stages of mitosis?
Prophase, Metaphase, Anaphase, Telophase
Describe prophase.
Chromosomes shorten and thicken to become visible.
Centrioles move to opposite ends of the cell and produce spindle fibres.
The nucleolus disappears and nuclear envelope breaks down.
Chromosomes are drawn towards the equator of the cell.
Describe metaphase.
By now each chromosome is seen to be made from two identical chromatids.
The chromatids are joined by a centromere.
Describe anaphase.
Centromeres divide into two, spindle fibres pull apart the chromatids.
The chromatids are now referred to as chromosomes and are at opposite poles of the cell.
If cells’ spindles are destroyed, anaphase cannot happen
Describe telophase and cytokinesis.
Chromosomes become longer and thinner, and disappear.
Spindle fibres disintegrate.
Nuclear envelope and nucleolus form.
Cytoplasm divides (cytokinesis)
How do prokaryotic cells divide?
Binary fission.
How do viruses replicate?
Not by division (as they are not alive). They inject the host cell with genetic information to cause the host cell to produce the components for a new virus.
What are the three stages of the cell cycle?
Interphase
Nuclear division
Cytokinesis (division of cytoplasm)
What is cancer caused by?
Damage to genes which regulate cell cycles/mitosis. This leads to uncontrolled cell division and growth, forming tumours. A tumour is cancerous if it is malignant.
What are three differences between benign and malignant tumours?
Slow vs rapid growth
Less compact vs more compact
Less likely to be life threatening vs more likely to be life threatening
How can cancer be treated?
Drugs can:
Preventing DNA being replicated
Inhibiting metaphase
However these drugs also affect normal cells. Fast replication cells (ie hair) are more affected.
