Story Us Flashcards
How does RNA differ from DNA?
- RNA is single stranded while DNA is double stranded.
- RNA has a sugar called ribose while DNA has a sugar called deoxyribose.
- RNA has the base uracil (U) while DNA has the base thymine (T).
What is mRNA?
Messenger RNA. It copies the
sequence of bases of a section of DNA in a process called transcription.
What tRNA
Transfer RNA. The tRNA picks up specific amino acids from the cytoplasm and brings them into position on the surface of a ribosome where they can be joined together in specific order to make a specific protein.
What is a gene?
A gene is a length of DNA which codes for a protein
What is a phenotype?
the visible characteristics that are created due to the protein that are coded by the genes.
What is an allele?
an alternate version of a gene
What does polygenic mean?
when two or more genes codes for a protein that determine the characteristic.
What is a dominant allele?
the dominant allele is expressed in the phenotype when present in the genotype.
What is a recessive allele?
the recessive allele is only expressed in the phenotype when present in the genotype with another recessive allele.
Genotype definition?
the alleles that an organism has for a particular characteristic
Homozygous dominant definition
carries only the dominant allele
Homozygous recessive definition
carries only the recessive allele
Heterozygous definition
carries both dominant and recessive allele
What happens when the genotype GG is reproduced with the genotype gg.
The dominant allele is always expressed.
What happens when the genotype Gg is reproduced with the genotype Gg?
75% of the time the dominant allele is expressed.
25% of the time the recessive allele is expressed.
This is expressed in the ratio 3:1
How many of our characteristics are polygenic?
All but one
What is the definition of codominance?
When multiple alleles contribute to the phenotype
Which chromosome is the sex chromosome?
chromosome 23
What genotype does a female chromosome have?
XX
What genotype does a male chromosome have?
XY
What is the ratio of having a girl to having a boy?
50:50
Describe the general process of natural selection?
1) There is variation with the species.
2) Changing conditions in the environment (selection pressure) favours some of the species.
3) The individuals with the mutated allele and favourable phenotype are more likely to survive and reproduce, therefore passing on the mutated allele.
4) Frequency of favoured phenotype increases under the environmental conditions.
5) Frequency of the less favourable phenotype decreases.
Describe how the process of natural selection can lead to bacterial resistance of antibiotics.
1) Random mutation causing a new allele for antibiotic resistance.
2) Selection pressure - exposure to the AB causes mutated allele has an advantage.
3) Therefore, the mutated allele/organism survive and reproduces.
4) Mutated allele passed on to the next generation.
5) Allele increases in population.
6) Over time a new species is created.
Where are chromosomes located?
the nucleus
What are the bases of DNA?
ADENINE which binds to THYMINE
CYTOSINE which binds to GUANINE
What is the difference of the bases in RNA?
RNA has uracil instead of thymine
What are the two stages of protein synthesis?
- Transcription
- Translation
What is the process of transcription?
- The two strands of the DNA helix are unzipped by breaking the weak hydrogen bonds between base pairs, this occurs because of the enzyme helicase.
- The enzyme RNA polymerase attaches to the DNA just before the gene.
- RNA polymerase moves along the DNA strand. RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing.
- RNA polymerase catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA.
What is the process of translation?
- 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. The three bases on mRNA are codons, this bind to the complementary three bases on the tRNA - the anticodon. We call this the triplet code.
- The tRNA molecules transport specific amino acids to the ribosome, the ribosome allows two tRNA molecules to sit next to each other and catalyses the formation of a covalent bond between the two amino acid.
- 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.
What happens to the polypeptide after translation?
It is folded to create a protein.
What is a mutation?
A mutation is a change in the sequence of bases in DNA.
What are the four types of mutation?
- Duplication
- Deletion
- Substitution
- Inversions
What are mutagens + mutagen examples?
Mutagens are chemicals which cause more frequent mutations. They include:
* ionising radiations (gamma rays, x-rays and ultraviolet light), and
* some chemicals, e.g. in tobacco.
What is a stem cell?
A cell that is not specialised it can either replicate itself or differentiate into many types of cell.
Differentiation definition?
The process of cells becoming specialised.
What are the two types of stem cell?
Embryonic and Adult
What are the features of an embryonic stem cell?
Found in the early form of an embryo they can differentiate into any type of cell.
What are the features of adult stem cells?
They are present in some tissues, they can differentiate into a few different types of specialised cell.
Uses of stem cells?
Stem cells can potentially be used to treat many different diseases. However there are questions around the ethics of harvesting embryonic stem cells.
Describe the differences between the process of transcription and translation?
- Transcription occurs in the nucleus whilst translation occurs in the cytoplasm/ ribosomes.
- Transcription uses DNA to make RNA whilst translation involves mRNA and tRNA.
- Transcription produces mRNA whilst translation produces amino acid chains / polypeptides.
- Transcription involves DNA being unzipped, whilst translation involves codons binding to anticodons.
Explain how a mutation can affect the phenotype of an organism / affect the functioning of an enzyme.
- Mutation is a rare and random change to DNA.
- It causes changes to bases.
- This means a change in the sequence of amino acids.
- This changes the enzyme/produces a different protein.
Explain why some mutations have little effect of the phenotype of an organism?
- change to bases may code for same amino acid.
- amino acid may not be involved in active site.
- enzyme still made
- could be recessive allele
- so not expressed in phenotype of an organism.
Genome definition?
The genome is the total DNA of an organism – coding for all its characteristics
Gene definition?
A gene is a short section of DNA within a chromosome - it codes for a specific protein.
Chromosome definition?
A chromosome is a straight (linear) strand of DNA. Most cells contain pairs of chromosomes - two strands with the same genes.
