DNA, Inheritance And Genetic Diseases Flashcards
Where is DNA found?
In chromosomes located in the nucleus
What is a gene?
A section of DNA that codes for a protein
What are the names of the different bases for DNA?
Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
What is a chromosome?
A thread like structure made up of DNA
What is DNA?
A double stranded polymer of nucleotides wound to form a double helix
What are nucleotides made up of?
- one deoxyribose sugar
- one phosphate
- one of the four bases
What are the complementary base pairs for DNA?
A and T
G and C
How are different parts of a nucleotide joined together?
(not which parts are bonded together)
By weak hydrogen bonds
Why are the hydrogen bonds joining the bases weak?
To allow the strands to separate and then rejoin together
Describe the method used to extract DNA from fruit
- Place a piece of fruit in a plastic bag, seal it then crush it
- Add extraction solution to the bag, then mix again
- Filter the solution
- Pour chilled ethanol into the filtered solution
- DNA precipitates forming a fibrous white solid
- Use a glass rod to collect the DNA sample
When extracting DNA, why is detergent in the extraction solution added to the crushed fruit?
It disrupts the cell membranes, releasing DNA into the solution
Why extracting DNA from fruit, why is the chilled ethanol added?
To precipitate the DNA to make it visible
What does the RNA polymerase do during the transcription phase of protein synthesis?
Binds to a non coding binding site and separates the strands of DNA. It moves along the DNA and starts making mRNA when it reaches the template strand.
What is RNA polymerase?
An enzyme that unwinds the DNA
What does DNA stand for?
Deoxyribonucleic acid
What does RNA stand for?
Ribonucleic acid
What are the 2 different types of RNA?
mRNA and tRNA
What is protein synthesis?
The formation of a protein from a gene
Name one difference between RNA and DNA
DNA is double stranded, RNA only has 1 strand
What is the name for a base pair triplet?
Codon
What is a codon?
A triplet of bases that codes for an amino acid
What is a polypeptide?
A chain of amino acids
Explain how a gene codes for a protein
A sequence of three bases in a gene forms a triplet, each triplet codes for an amino acid. The order of amino acids determines the structure and function of protein formed.
Why is the folding of amino acids important in proteins like enzymes?
It determines the shape of the active site, which must be highly specific to the shape of its substrate.
What are the two stages of protein synthesis?
Transcription and translation
Describe what happens in transcription
- RNA polymerase binds to a section of non-coding DNA and unwinds the DNA into two strands
- The RNA polymerase joins free RNA nucleotides to complementary bases, forming an mRNA strand
- The mRNA then leaves the nucleus and the DNA returns to its double helix form.
What is tRNA?
A form of RNA that carries a specific kind of amino acid, to be used in protein synthesis
Describe what happens in translation
- mRNA attaches to a ribosome
- The ribosome reads the mRNA bases in codons which each code for one amino acid
- The amino acids are brought to the ribosome by tRNA and join together to form a polypeptide chain which folds to form a protein
Which 2 people worked out the structure of DNA?
James Watson and Francis Crick
What is a mutation?
A change in the DNA base sequence of a gene
What is a phenotype?
An organisms viable characteristics
What is a genotype?
The alleles for a certain characteristic
What is an allele?
A version of a gene
What 3 main things can cause mutations?
- Radiation
- Chemicals
- Infectious agents
What is a genetic disorder?
A disease caused by a mutation
Explain how a mutation might lead to a faulty protein (6 marks)
- A mutation is a change in the base sequence of a gene
- A change in a single DNA base would change the codon
- This might change the amino acid it codes for when being translated at the ribosome
- This would change the amino acid sequence for the protein so it will fold differently
- This might stop the protein functioning or change how it functions.
Where do an organisms alleles come from?
One from each parent, making up the genotype
What were Gregor Mendel’s laws of inheritance?
- Each gamete receives only one of the alleles for a gene
- Which allele a gamete receives is random
- Some alleles are dominant, others are recessive
Why did scientists find it difficult to explain inheritance in humans before the 20th century?
They had weaker microscopes and didn’t know about DNA or genes
What is a homozygous genotype?
When both alleles making up the genotype are the same
What is a heterozygous genotype?
When both alleles making up the genotype are different
MM is an example of ____________ __________
Homozygous dominant
Mm is an example of ____________ __________
Heterozygous
mm is an example of ____________ __________
Homozygous recessive
What was the purpose of the Human Genome Project?
To work out all the possible genes for humans and the different base sequences
What is the purpose of genetic screening?
To check for hidden genes like a genetic disease or to see if someone is a carrier of a genetic disease
What is an advantage of genetic screening?
You can work out the possibility of a child having a certain disease
What is genetic variation? What causes it?
Having different characteristics as a result of a mutation or sexual reproduction
What is environmental variation?
Characteristics caused by an organisms environment
What are acquired characteristics?
Characteristics that are developed over time due to the environment
What is continuous variation?
Variation measured in values that can change gradually over time eg. height
What is discontinuous variation?
Variation that isn’t measured as number values
What is agglutination?
The clumping together of red blood cells
What does it mean for 2 alleles to be codominant?
Neither of the 2 alleles are dominant over the other so both alleles will be expressed in the phenotype
An allele that will only affect the phenotype if 2 copies are present is known as __________
Recessive
What is a genome?
All the DNA in an organism
What is the name for a gene located on a sex chromosome?
A sex-linked gene
Are sex linked disorders dominant or recessive?
Recessive
Which chromosome are genes for sex linked disorders are normally located in humans?
X chromosome
Why can’t fathers pass on sex-linked disorders to their sons?
The father would have to pass the Y chromosome to his son, sex-linked disorders are located on the X chromosome.
What are the complementary base pairs for RNA?
A and U
G and C
What are the names for the different bases for RNA?
Adenine (A), Uracil (U), Guanine (G), Cytosine (C)
Describe the structure of a nucleotide
Phosphate joined to a sugar which is joined to a base
How can genetic variants in the non-coding DNA affect the phenotype?
It changes the amount of RNA polymerase that can bind to the region and therefore the quality of protein produced
How can genetic variants in the coding region of DNA affect the phenotype?
This will alter the sequence of bases which could change the amino acid it codes for which would change the protein produced
