Chapter 7 - Information of life Flashcards
What does DNA do?
Holds the genetic information
What does DNA stand for?
Deoxyribose nucleic acid
What is DNA made of?
A polymer of nucleotides
What is a nucleotide?
A phosphate, a five-carbon sugar and an organic base
What are the organic bases in DNA?
Adenine
Thymine
Cytosine
Guanine
What is the five-carbon sugar in DNA?
Deoxyribose
What are the complementary base pairs?
Adenine and thymine
Cytosine and guanine
What bases are the pyramidenes?
Cytosine and thymine
What bases are the purines?
Adenine and guanine
How are the polynucleotide chains formed?
By condensation reactions
How many polynucleotide chains are in DNA?
2
How many hydrogen bonds link cytosine and guanine?
3
How many hydrogen bonds link adenine and thymine?
2
How is the structure of DNA related to its function of storing genetic information?
The sugar-phosphate backbone makes the molecule stable
The molecule coils up so it is compact i.e. store a lot of information in a small space
The sequence of bases allows it to carry coded information for making proteins
It is a very long molecule so can store lots of information
Complementary base pairing allows the molecule to replicate itself accurately
The double helix makes the molecule stable - the base pairs are on the inside so are less likely to be damaged
Bases are held together by hydrogen bonds which allow the molecule to unzip easily when it replicates
The sugar-phosphate backbones run what to each other?
Antiparallel
What helix structure does DNA have?
Double helix
What does RNA stand for?
Ribonucleic acid
What five-carbon sugar does RNA’s nucleotides contain?
Ribose
What four bases are in RNA?
Adenine, cytosine, guanine and uracil
What does uracil replace in RNA and what does it pair with?
Thymine
Pairs with adenine
How many polynucleotide strands does RNA have?
1
State the differences of RNA compared to DNA
Single polynucleotide chain as opposed to double
Five-carbon sugar is ribose instead of deoxyribose
Uracil pairs with thymine instead of A-T
RNA is much shorter than DNA
How many bases code for one amino acid?
3
How does the sequence of bases affect what protein is made?
The sequence of bases codes for the order of amino acids in the protein
Where is DNA found?
In the cell nucleus
Where are proteins made?
In ribosomes
What is the role of RNA?
To make proteins from information from DNA
What is a gene?
A section of DNA that carries coded information about a characteristic
What is transcription?
DNA to mRNA
What is translation?
mRNA to protein
How does RNA carry out its role?
The base sequence of the gene is copied into an RNA molecule
It then passes through a nuclear pore (does this easily because it is single stranded and short)
mRNA carries the information to the ribosome
tRNA brings amino acids to the ribosome and joins them in the rig order
The correct protein is made (in primary structure)
What is the RNA world hypothesis?
A primitive living thing would need a metabolism to grow, so would presumably need enzymes
It would also need to replicate itself, so would need genetic material
Did DNA or proteins come first?
What do some scientists think about this?
That RNA acted as an enzyme and genetic material, and that DNA evolved later
Why is DNA a better genetic material than RNA?
Cytosine can break down into uracil, so if this happens, the DNA repair enzymes can spot the error
How is human DNA arranged?
In chromosomes
How many pairs of chromosomes do humans have?
23
What is a homologous pair of chromosomes?
A pair of chromosomes which have same genes but different alleles
Where do genes occur on homologous chromosomes?
At the same relative position (locus)
What is an allele?
An alternative form of a gene
What is phenotype?
The characteristics of an organism as a result of its alleles
How do alleles cause cystic fibrosis?
Two faulty (recessive) alleles coding for a faulty CFTR protein
How is the faulty CFTR protein different to the normal CFTR protein?
It is a different shape
How many nucleotides does the cystic fibrosis allele have missing?
Why does this create a faulty CFTR protein?
3
Three nucleotides code for one amino acid, so this one missing amino acid affects the protein
Why does the one missing amino acid cause such significant problems?
Proteins form a complex tertiary structure, created by bonds in the R-groups of amino acids
Because 1 amino acid is missing, the shape is different, therefore can’t function properly
Proteins can also act as what?
Enzymes
What does the active site of an enzyme depend on?
The tertiary structure of the protein
What does the tertiary structure of a protein depend on?
The order of amino acids in the protein
What does the order of amino acids in a protein depend on?
The sequences of bases in the DNA molecule
What makes alleles slightly different to each other?
Slightly differing base sequences in the DNA
How do different alleles produce different proteins?
If the order of bases are different, so is the order of amino acids.
If the order of amino acids are different, the tertiary structure is different.
If the tertiary structure is different, the active site is altered.
What is the problem with some proteins produced by different alleles?
They can’t form enzyme-substrate complexes due to the different active site
However, some enzymes can still function more or less efficiently than another allele’s protein
When does DNA copy itself accurately?
When a cell divides
What method does DNA replicate itself by?
Semi-conservative method
What is the first stage of replication?
The two strands of DNA separate because the hydrogen bonds between the bases break
What happens once the two strands are separated?
Free nucleotides in the nucleus are attracted to their complementary bases
What happens after this complementary base attraction?
Once the nucleotides have lined up, DNA polymerase joins them together
Why is it called the semi-conservative method?
Each strand retains half of the original DNA material
In what phase does DNA replication occur?
Interphase
What did the conservative method propose?
The original DNA molecule stayed intact and that a new molecule, exactly the same as the first, would be built up entirely of new nucleotides
What did dispersive replication suggest?
The original DNA molecule would break down
Nucleotides would be replicated, then two new identical molecules would be assembled
Each daughter molecule would be a mixture of old and new nucleotides, randomly distributed between them
What are the two other disproven methods of replication?
The conservative method, and the dispersive method
