OCR Biology F215 Cellular Control and Variation

Very detailed revision cards of the whole first module of F215: Cellular Control and Variation :)

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  • Created by: Adi
  • Created on: 07-05-13 18:08
What do genes code for?
Polypeptides, including enzymes
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What is the meaning of the term "genetic code"?
The genetic code is the 3 letter code by which information is contained in a DNA molecule.
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How does a nucleotide sequence code for a polypeptide chain?
A group of 3 bases (e.g GTC) codes for a specific amino acid (e.g Valine) to be added to a growing polypeptide chain.
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Why does Protein Synthesis take place outside of the nucleus?
Because the DNA is too large to exit through the nuclear pores and it is good to keep the DNA away from any metabolic reactions taking place in the cytoplasm.
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How does the DNA get to the ribosomes in the cytoplasm?
It undergoes a process called transcription where the DNA is copied to make an mRNA copy. mRNA then leaves the nucleus via the pores and moves to the ribosomes.
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What are the 2 stages of Protein Synthesis?
Transcription (where the instructions on part of a DNA are copied to a mRNA molecule) and Translation (where the mRNA takes the instructions to a ribosome and they are used to build a polypeptide)
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What is the names of the enzymes involved in Translation?
DNA helicase and RNA polymerase
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What is Codon?
A codon is a set of 3 bases on mRNA e.g AUG. It codes for a certain polypeptide.(e.g Methionine)
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What is an Anticodon?
The 3 exposed bases at one end of a tRNA molecule. This pairs with the codon to ensure the right amino acid is its correct place.
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What is the name of the enzyme involved in Translation? What do they do?
tRNA transferase. They load specific amino acids to specific tRNA molecule and there are different types for each tRNA molecule.
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How is the mRNA molecule held on a ribosome?
The mRNA molecule is held in the cleft of the ribsome with 6 of its bases exposed (2 codons)
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How and what bonds are formed between the amino acids?
A condensation reaction occurs and a peptide bond is formed.
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What is 1 way a mutation has a neutral effect on the way a protein functions?
1. The mutation changes a base in a sequence, but amino acid that the triplet codes for doesn't change.
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What is 1 example of a disadvantageous mutation on a proteins function?
Cystic Fibrosis. It is caused by a deletion of 3 bases in the gene that codes for the CFTR protein. This then folds incorrectly so its broken down. (leads to excess mucus + lung problems)
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How does cyclic AMP activate proteins?
By altering their 3-dimensional structure.
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What are the 2 enzymes which help with the digestion and absorption of glucose?
B Galactosidase (hydrolyses lactose to glucose and galactose) and B Galactoside Permease (enables the cell to take up glucose)
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When are the genes that code for these enzymes switched on and off?
They are switched on when the E. coli is grown on a medium of lactose and switched off when they are grown on a medium of glucose.
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When does RNA polymerase stop making mRNA?
When it reaches a STOP codon.
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What is an operon?
An operon is a section of DNA that contains, structural genes, control elements and sometimes a regulatory gene.
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What does a regulator gene code for?
A repressor protein.
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How does a repressor protein work when lactose is not present?
The repressor protein binds with the operator site, preventing RNA polymerase from going ahead with transcription
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How does a repressor protein work when lactose is present?
The lactose binds with the repressor protein, changing it's shape so that it can no longer bind with the operator site. RNA polymerase can now begin transcription of the structural genes.
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What do Homeotic genes code for?
The proteins which control the development of body plans. e.g so that evertything grows in the right place
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What does it mean by 'the homeotic genes are highly conserved?'
The homeotic genes are very similar in all animals. They are also similar in plans and fungi (but not compared to animals). They have not changed much in billions of years.
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What are Homeobox sequences?
Regions on the homeotic genes that code for part of the protein called the Homeodomain.
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What is the function of the Homeodomain?
It acts as a transcription factor on DNA by binding to specific sites at the beginning of developmental genes. By activating/repressing transcription it alters the production of proteins involved in the body plan.
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What is Apoptosis?
Apoptosis is controlled process where cells die
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Why is Apoptosis important in the development of a body plan?
It ensures the correct plan develops. E.g Fingers and toes and tails on tadpoles
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What is the definition of an allele?
One of two alternatives of a gene. As a human cell has 2 copies of each gene, the cell could therefore contain 2 different alles of that gene.
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What is the definition of a locus?
A locus is the position on a chromosome at which a particular gene is found. (Both of the chromosomes of a homologous pair carry genes for the same feature at the same place)
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What is the definition of a phenotype?
An organisims phenotype is their observable characteristics (the genes that are expressed)
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What is the definition of a genotype?
The alleles of a particular gene(s) possessed by an organism. 3 possible genotypes because there are 2 copies of each gene (FF Ff ff). Genotype where both are the same is homozygous (FF) different is heterozygous (Ff)
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What is the definition of dominant?
A dominant allele has an effect whether or not a recessive allele is present.
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What is the definition of Codominant?
Codominance is when both alleles have an affect on the phenotype in a heterozygous organism. E.g Blood group inheritance
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What is the definition of recessive?
A recessive allele only has an efect on the phenotype when the dominant allele is not present
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What is 'linkage'?
Linkage is the presence of 2 genes of the same chromosome, so that they tend to be inherited together and do not assort independently.
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What is 'crossing over'?
The exchange of alleles between chromatids of homologous chromosomes as a result of chiasma formatiob during prophase of Meiosis 1.
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When in Meiosis does Independent Assortment occur and how does it produce variation?
Metaphase 1. Different combinations of maternal and paternal chromosomes go into each cell, so each new cell sends up with a different combinatiob of alleles.
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How does fertilisation create variation?
Any egg can fuse with any sperm
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What is epistatis?
Epistatis is an interactionof 2 or more different genes to produce a particular phenotype (one gene can mask the expression of the other)
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What is the ratio of a dihybrid cross involving a reccessive epistatic allele?
9:3:4
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What is the ratio of a dihybrid cross involving a dominant epistatic allele?
12:3:1
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What is continuous variation?
Where individuals in a population vary within a range e.g finger length or plant mass. It is controlled by 3 or more genes (or alleles on the genes) and said to be polygenic.
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What is discontinuous variation?
Where there are 2 or more distinct categories - each individual falls into only one of these e.g sex or blood group. It is typically controlled by 1 gene and said to be monogenic.
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How can the environment control variation?
Differences in the environment e.g food, climate, lifestyle. E.g Accents are determined by environmental factors only
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How can both environment and genetics together control variation?
Genetic factors determine genotype and characteristics the organism is born with but environmental factors can determine how those characterisics develop. Most phenotypic variation is a result of both and usually shows continuous variation.
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What is the Hardy-Weinberg equation to find out allele frequencies in a population?
p + q = 1 ( p = dominant and q = recessive)
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What is the Hardy-Weinberg equation to find out genotype frequency in a population?
p2 + 2pq + q2 = 1
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What is Stabilising Selection?
When the environment isnt chaning much, individuals are usually well adapted to the environment. The alleles present already confer the most advantageous characteristics. The range of possible phenotypes is reduced.
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What is Directional Selection?
When there's a change in the environment, individuals with extreme types are more likely to survive and reproduce. It can also occur by a random mutation or new alleles in the gene pool from an immigrant individual into the population.
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What is Genetic Drift?
Genetic drift is a change in the characteristics of a population or the proportions of different alleles in a population as a result of a chance.
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hat are 2 examples of how genetic drift can occur?
One or two individuals may have better breeding success (more common alleles) and alleles of individuals who didnt breed are lost(less common)
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Why is genetic drift more likely to occur in small populations?
Because chance has a greater infulence on small populations. In large populations, these changes would be evened out.
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What is speciation?
The formation of a new species. ( when it is morphologically/physiologically different to each other and can no longer produce fertile offspring.
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What is ecological (geographic) isolation?
When organisms are separated by a physical barrier and conditions on either side may be different. This means different alleles will be advantageous on either side etc....
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What is seasonal (temporal) isolation?
Two species may not be active at the same time of day or do not reproduce at the same time of year.
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What are 3 examples of reproductive barriers?
2 species may not be able to breed successfully due to factors like different courtship behaviour, mechanical problems with mating and gamete incompatibilty.
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What is the biological species concept?
The tradition definition given to a species. A group of organisms that can breed together to produce fertile offspring.
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What are the limitations with the biological species concept?
You cannot always observe the reproductive behaviour. They could be extinct, reproduce asexually or there may be practical/ethical issues.
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What is the phylogenic species concept?
The phylogenic species concept suggests that a species is that that has the same ancestor. At some point in the progress of this group, some may diverge. It is only when such divergance becomes sufficiently clear, that they can be classed as seperate
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What are the limitations of the phylogenic species concept?
The is no "cut off" to say how different 2 species have to be in order to be seperate from one another.
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What is a similarity of natural selection and artifical selection?
Both change the allel frequencies in the next generation (the alleles with the most beneficial/desirable trait will be more common in the next generation)
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What is a difference between natural selection and artificial selection?
Natural selecton makes the species better adapted to the environment but artificial selection makes the species more useful for the humans.
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How do farmers use artificial selection to improve milk yield of their cows?
1. They take a female with a high milk yield and a male whos mother has a high milk yield. 2. they breed them together and select the offspring with the highest milk yield. 3. They breed them together and repeat for many generations.
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How do farmers use artificial selection to improve wheat yield of their crops?
1. wheat plans with a high wheat yield are bred together. 2. the offspring with the highest yield are bred together. 3 .this is repeated over several generations to produce a crop with a very high wheat yield
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Other cards in this set

Card 2

Front

What is the meaning of the term "genetic code"?

Back

The genetic code is the 3 letter code by which information is contained in a DNA molecule.

Card 3

Front

How does a nucleotide sequence code for a polypeptide chain?

Back

Preview of the front of card 3

Card 4

Front

Why does Protein Synthesis take place outside of the nucleus?

Back

Preview of the front of card 4

Card 5

Front

How does the DNA get to the ribosomes in the cytoplasm?

Back

Preview of the front of card 5
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