Story of Us : part 2 Flashcards
1
Q
what does DNA contain?
A
- the information needed to make a protein
2
Q
what codes for a specific amino acid?
A
- three bases (a codon)
3
Q
what is the sequence of bases?
A
- a set of instructions for which order to join amino acids in to make a protein
4
Q
what is mRNA?
A
- a copy of DNA
5
Q
what does mRNA do?
A
- moves from the nucleus to the ribosomes where proteins are synthesised in the cytoplasm
-the protein produced depends on the sequence of bases in the mRNA, and if this sequence changes, a different protein will be made
6
Q
what is tRNA?
A
- carrier molecules
7
Q
what does tRNA do?
A
- brings specific amino acids to add to the growing protein in the correct order
8
Q
how many amino acids are there?
A
- only about 20 differently naturally-occurring amino acids
9
Q
how many amino acids are there in each protein molecule?
A
- has hundreds or even thousands of amino acids joined together in a unique sequence
10
Q
what has to happen to the unique sequence of amino acids?
A
- folded into the correct unique shape
- this is v important as it allows the protein to do its job
11
Q
what jobs do proteins have?
A
- some proteins are enzymes, others are hormones and others form structures within the body, such as collagen
- each of these proteins needs a different shape
12
Q
how do cells express their genes?
A
- by converting the genetic message into protein
13
Q
what two stages does the process of protein synthesis occur in?
A
- transcription
- translation
14
Q
what is transcription?
A
- when a gene is to be expressed, the sequence of bases in RNA is copied or transcribed into mRNA (messenger RNA)
- this process takes place in the nucleus and occurs in a series of stages
15
Q
describe transcription.
A
- the two stands of DNA helix are unzipped by breaking the weak hydrogen bonds between base pars. the unwinding of the helix is caused by an enzyme (helicase)
- the enzyme RNA polymerase attaches to the DNA just before the gene
- RNA polymerase moves along the DNA strand. free RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing
- RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA
- the newly formed of mRNA is now ready to leave the nucleus and travel to the ribosome
16
Q
what are the bases of RNA nucleotides?
A
- contain the same bases as DNA, except that T is replaced by U. U base pairs with A
- because the opposite base bonds with the exposed DNA bases, the strand of mRNA is an opposite copy of the DNA strand (except that U replaces T).
- we call this a complementary copy
17
Q
describe translation.
A
- the mRNA strand travels through the cytoplasm and attaches to the ribosome. the strand passes through the ribosome.
- for every three mRNA bases the ribosome lines up one complementary molecule of tRNA. we call every three bases on mRNA a codon. the complementary three bases on the tRNA are an anticodon. e.g. if CGG is the mRNA codon, the tRNA anticodon is GCC - the triplet code
- tRNA molecules transport specific amino acids to the ribosome. the ribosome allows two tRNA molecules to sit next to each other; the ribosome catalyses the formation of a covalent bond (peptide bond) between the two amino acids.
- used tRNA molecules exit the ribosome and collect another specific amino acid
- a chain of several hundred amino acids forms in the correct order according to the original DNA is then made. this is called a polypeptide
18
Q
what happens after translation?
A
- the polypeptide is finally folded into the correct shape and becomes a protein
18
Q
what is a result of sexual reproduction?
A
- variation in genes
- new forms of genes can result from mutations
19
Q
what is a mutation?
A
- a change in the sequence of bases in DNA
20
Q
what would cause a change in the sequence of bases in DNA?
A
- this can be due to the replacement of a single base pair with a different pair, or an addition or deletion of one or more base pairs.
- this gives a change in the DNA sequence which in turn changes the sequence of amino acids in the protein
- this will normally alter the shape and function of the protein
21
Q
what is chromosomal mutation?
A
- when a cell gains an extra chromosome (such as Down’s Syndrome) or one part of a chromosome is stuck onto another chromosome
22
Q
are mutations common in eukaryotes?
A
- mutations are comparatively rare events in eukaryotes as our cells can detect and correct many mistakes in the DNA sequence
23
Q
are chromosomal mutations harmful?
A
- they are almost always harmful, as they result in over or underproduction of proteins
24
Q
are changes in the DNA sequence harmful?
A
- changes in the DNA sequence are often neutral , meaning they have no effect, but can less often be either positive, ie increasing variation and my be beneficial if the environment changes, or negative ie the proteins failing to work properly
25
Q
what happens if the mutation occurs during meiosis?
A
- if the mutation occurs during meiosis in gamete formation it will affect all of the cells in the individual which develops from the gamete
- this means that the mutation is inherited
26
Q
what happens if the mutation occurs in a body cell?
A
- it will affect only those cells produced by mitosis from the affected cell
- mutations in body cells give rise to cancers of the cells that are affected
- this type of mutation is not inherited
27
Q
what are mutagens?
A
- chemicals which cause more frequent mutations - they include ionising radiations (gamma rays, x-rays and ultraviolet light) and some chemicals , e.g. in tobacco
28
Q
what do mutations increase in a population?
A
- genetic variation
29
Q
what do all cells begin as?
A
- stem cells
30
Q
what are stem cells?
A
- they are not specialised to a particular job but are able to divide many times by mitosis to make new cells
- some stem cells then differentiate (develop new features) to become specialised cells- ones which have the structures and proteins needed to carry out a specific job in the organism
31
Q
what is differentiation controlled by?
A
- the genes
32
Q
what are happened to genes during differentiation?
A
- they are ‘switched off’ (silenced) so they cannot be transcribed
- this ensures the only proteins produced in the specialised cell are the ones needed to carry out its particular job
33
Q
what are the two different types of stem cell in humans?
A
- embryonic
- adult
34
Q
what are embryonic stem cells?
A
- they are found in the early form of an embryo
- they can differentiate into any type of cell
35
Q
what are adult stem cells?
A
- they are present in some tissues in organisms (from the time they have recognisable organs)
- there are several different types
- they divide by mitosis and each type of stem cell can differentiate into a few different types of specialised cell
- e.g. bone marrow stem cells can only form blood cells and bone cells
36
Q
what can stem cells be used for?
A
- they can potentially be used to treat many different diseases, repair damaged tissues and even grow new organs for transplant
37
Q
what can we do with adult stem cells?
A
- transplant them
- e.g. if someone has a damaged immune system they may receive a bone marrow transplant
- adult stem cells are easy to collect for treatment, but can only become a limited number of cell types
38
Q
what do scientists do with embryonic stems?
A
- they collect them and culture them and grow large numbers in a lab
- they are investigating how to instruct these cells to form different types of tissue for medical treatment
- many object morally to this research - the cells come from extra embryos which weren’t used in IVF treatments
39
Q
what is a disease?
A
- a condition which prevents the body or part of it working properly
40
Q
what are most diseases caused by?
A
- microorganisms (pathogens) entering the body and feeding and reproducing in it
- in doing so, they may damage the body or poison it by excreting toxic waste substances called toxins
41
Q
what are the main organisms which cause diseases?
A
- very small - microorganisms like viruses and bacteria
42
Q
what prevents these microorganisms which can cause disease from entering the body?
A
- the skin and membranes of the body act as physical barriers
43
Q
what are the two main types of white blood cells?
A
- phagocytes
- lymphocytes
44
Q
how do phagocytes work?
A
- phagocyte recognises pathogen
- phagocyte engulfs pathogen in a process known as phagocytosis
- the lysozymes containing enzymes move towards the pathogen
- enzymes break down pathogen
- useful materials are absorbed
- waste products are removed from phagocyte
45
Q
what are phagocytes?
A
- they are type of white blood cell that engulf and digest pathogen that they encounter
- this process is called phagocytosis
46
Q
what do lymphocytes produce?
A
- special Y shaped proteins called antibodies
47
Q
what do antibodies do?
A
- these attach to proteins on the surface of pathogens called antigens
- each pathogen has a different shaped antigen, so the lymphocytes need to make a specific complementary antibody
48
Q
what do lymphocytes do?
A
- they allow organisms to build up an immunity towards certain diseases
49
Q
how do lymphocytes work?
A
- lymphocytes detect pathogen’s antigens
- lymphocyte identifies the correct type of antibody to make, which is complementary to the pathogen’s antigen
- lymphocyte releases large numbers of correct antibody
- pathogens either clump together resulting in death or the antibodies trigger phagocytes. some pathogens can even burst.
- lymphocytes produce cells that produce lots of the antibody very quickly if they detect the same pathogen again. these are called memory cells
50
Q
what are anti-toxins?
A
- some antibodies are specialised to combat toxins, chemicals released by the pathogen which cause cell damage.
51
Q
what do lymphocytes do to prevent the body being infected by the same pathogen time and time again?
A
- they produce memory cells
- these can remain in our circulatory system for a lifetime
52
Q
how do we gain immunity from pathogens?
A
- when the body next encounters that same pathogens, the memory cells react to the pathogen very quickly, producing lots of antibodies much earlier than the first time.
- this kills the pathogen before we feel ill and so prevents us being infected twice by the same pathogen
- we are said to have gain immunity
53
Q
how do vaccines work?
A
- the body is given a vaccine, which is a dose of the pathogen, normally by this injection
- this dose is either the dead pathogen or parts of the pathogen’s cell surface
- this stops the pathogen from causing a disease
- the lymphocytes generate antibodies against the pathogen and more importantly, make memory cells
- this way, vaccines can give us immunity
54
Q
what is natural selection?
A
- the theory commonly called “survival of the fittest”
- proposed by Charles Darwin
- one of the most important theories in science since it gives an explanation for the origin of humans and is the ‘driving force’ behind evolution.
55
Q
what year and in which book was the theory of natural selection put forward?
A
- 1859
- the origin of species
56
Q
which observations was Darwin’s theory based on?
A
- all living things/organisms show variation
- all living things tend to over-reproduce
57
Q
what did Darwin conclude from his observations?
A
- there will be a ‘struggle for existence’ because organisms over reproduce, and therefore resources will be limited
- some will be better adapted to their environment than others because they vary
- those best adapted will survive and reproduce in greater numbers than the less well adapted Darwin called this ‘survival of the fittest’
58
Q
using what we know now, why does variation occur?
A
- due to mutations, which occur randomly and continuously
59
Q
using what we know now, why are some individuals within a population more able to survive in the environment?
A
- some individuals within a population will have specialisations which make them more able to survive in the environment - they may be able to get more food, or have features which mean they can cope with the temperature better
- these individuals with better specialisations are more likely to survive to reproduce and will pass on their advantageous alleles to the next generation, therefore the offspring will tend to inherit the advantageous characteristics
- less favourable alleles tend to become less common in the population
- this repeats for many generations
- over time, the specialisations which help organisms to survive will become more common and the characteristics of a species will change and we will end up referring to them as a different species
60
Q
what are antibiotics?
A
- chemicals which kill bacteria and do not usually harm animal cells
61
Q
how do antibiotics manage to not harm animal cells whilst killing bacteria?
A
- they achieve this by targeting cell structures such as bacterial cell walls, which animal cells do not contain
62
Q
how many years have antibiotics been in use for?
A
- around 80 years
63
Q
what is a major issue facing the world today regarding antibiotics?
A
- antibiotic resistance
- many antibiotics are not working
- the discovery of new types has slowed
64
Q
why aren’t antibiotics working?
A
- due to natural selection occurring in response to the overuse of antibiotics, in particular the first antibiotic penicillin
65
Q
describe the process of antibiotic resistance.
A
- originally, none of the bacteria were resistant and penicillin was not used
- doctors began to use penicillin, which killed the bacteria
- a chance mutation gave some bacteria resistance to the antibiotic
- these bacteria were better adapted to an environment in which penicillin was used
- they survived in greater numbers. as there are fewer non-resistant bacteria there is less competition for resources
- so the resistant bacteria reproduce rapidly and passes on the resistance allele
- this was repeated with each generation of bacteria
- the proportion of bacteria with the resistance allele increased until most had the allele
