Topic 1- The Building Blocks of Cells Flashcards
What did the first light microscopes allow scientists to see?
small, single-celled organisms and the cells that made up larger life
How do light microscopes work?
they use glass lenses to refract light and produce a magnified image
What is the calculation for the magnification of a light microscope?
multiply the magnification of the eye piece lens by the objective lens
How do electron microscopes work?
instead of using light, they shine a beam of electrons through a sample
What is the difference between the wavelength of electrons and the wavelength of light?
the wavelength of electrons is much smaller than the wavelength of light
Why might a scientist choose to use an electron microscope rather than a light microscope?
the wavelength of electrons is much smaller than the wavelength of light, and this means that a much greater magnification and detail can be seen
What are the 4 main features of an animal cell?
1- nucleus
2- cytoplasm,
3- cell membrane
4- mitochondria
What are the 7 main features of a plant cell?
1- nucleus 2- cytoplasm 3- cell membrane 4- mitochondria 5- cellulose cell wall 6- large vacuole (almost always) 7- chloroplasts (those that are exposed to light)
What are the 5 main features of a bacterial cell?
1- cytoplasm 2- cell wall (non-cellulose) 3- plasmid DNA 4- chromosomal DNA 5- Flagella
How many pairs of chromosomes are in normal human cells?
23 pairs
What do chromosomes consist of?
long, coiled molecules of DNA
what does DNA stand for?
deoxyribonucleic acid
What is a gene?
a section of DNA which codes for a particular protein
What does a DNA molecule consist of?
Two strands, which are coiled to form a ‘double helix’. The strands are linked by a series of paired ‘complementary bases’.
What are the names of the 4 complementary bases in DNA?
adenine (A), cytosine (C), guanine (G), and thymine (T)
What does adenine link to (and vice versa)?
adenine only ever links to thymine (A-T)
What does cytosine link to (and vice versa)?
cytosine only ever links to guanine (C-G)
What are the complementary bases held together by?
weak hydrogen bonds
(H) Who was Fred Sanger?
A biochemist, who, in 1977, discovered a way of identifying the sequence of bases in DNA.
(H) What is a genome?
A genome is all of the genetic material in an organism
(H) What were the aims of The Human Genome Project?
- to work out the order or sequence of all the three billion base pairs in the human genome
- to identify all the genes
- to develop faster methods for sequencing DNA
(H) Why might knowing where a gene appears on a chromosome and how it is made up, be useful for doctors?
doctors could identify and replace ‘faulty’ genes which cause genetic disorders
(H) Why might knowing where a gene appears on a chromosome and how it is made up, be useful for forensic scientists?
forensic scientists could use the information to compare DNA samples from potential suspects with those found at a crime scene, and therefore convict or clear them of the crime
Who were the four scientists involved in the discovery of the structure of DNA?
James Watson, Francis Crick, Rosalind Franklin and Maurice Wilkins
Who discovered the double helix model of DNA?
James Watson and Francis Crick, in 1953
How did Franklin and Wilkins investigate the structure of DNA?
they took an X-ray diffraction image of DNA
What is the basis of genetic engineering?
it involves removing a gene from one organism and inserting it into another
If genes from one species are inserted into animals of a different species, what are they called?
‘transgenic’ animals
Transgenic cows have been created to produce ‘designer milk’. What does this milk contain?
- extra protein (casein)
- low levels of cholesterol
- human antibodies (normally produced by our white blood cells)
How has rice been genetically modified to benefit humans?
rice has been genetically modified to contain a beta-carotene gene to reduce Vitamin A deficiency in humans. Vitamin A deficiency can lead to blindness in children.
How can genetic modification benefit diabetics?
the human gene for insulin has been inserted into bacteria, which are then used to produce insulin on a larger scale to treat diabetics
What are herbicides used for?
to kill weeds, which prevent crop plants from growing
