1.4 DNA and protein synthesis Flashcards
describe the structure of an nucleotide
- Phosphate group ,5 carbon sugar and a nitrogenous base
Name the pentose structure in DNA and RNA
DNA = Deoxyribose
RNA = ribose
Describe how a poly nucleotide is formed
- Condensation reaction happens between nucleotides to form strong phosphodiester bonds.
What is the difference between a pruine base and nitrogenous base
Purine bases - Have two nitrogen containing rings. In DNA these are Adenine and Guanine
Nitrogenous base - Have one nitrogen containing rings. In DNA these are cytosine and thymine and in RNA this is cytosine and uracil
40% of a nucleotide in a sample of DNA contained the base guanine. Calculate the proportion of the other nucleotides
40 % guanine : 40% cytosine
10 % adenine : 10% thymine
What are some differences in RNA and DNA
- DNA found in nucleus and RNA found in cytoplasm
- DNA molecules are very long molecules where as RNA are relatively short compared to DNA .
-DNA has a double helix structure of two polynucleotide chains , where as RNA is just polynucleotide strand
Why is DNA replication important?
Because when a cell divides into two, both daughter cells must contain a full set of DNA
What phase does DNA replication take place ?
Interphase
Explain the role in DNA helicase in DNA replication
- Catalyses the breaking of the hydrogen bonds between base pairs to un ravel double helix
Why is DNA replication described as Semi conservative ?
Stands from DNA molecules act as templates , new DNA molecule contains one old DNA strand and one new.
Describe the process of DNA replication
- DNA helicase attaches to DNA molecule and catalyses the breaking of hydrogen bonds between bases to unwind strand.
-Free nucleotides line up against their complimentary bases on the DNA strand
-Then DNA polymerase moves down the DNA molecule and catalyses the formation of phosphodiester bonds between the free nucleotides and DNA strand. (Condensation)
-DNA ligase joins up the shorter strands of polynucleotides on the lagging strand of DNA.
Why is it important that the activated nucleotides lose two phosphate groups when bonded to the DNA
This provides energy for the reaction (ATP)
What are the two different isotopes of nitrogen
Nitrogen 14, light
Nitrogen 15, heavy
) Describe how the process of DNA replication produces two identical DNA molecules.
(4)
1 - Hydrogen bonds between nucleotides are broken by DNA helicase
2 -Complementary nucleotides bind to the exposed strands.
3 - Hydrogen bonds will only form between cytosine and guanine and thymine and adenine
4 - Leading strand is synthesised continuously but lagging strand requires DNA ligase to join up okazaki fragments
What is a gene ?
A sequence of bases on a DNA molecule coding for a sequence of amino acids on a polypeptide chain
What are every three bases called on DNA
A codon
What do codons read for ?
A specific amino acid,
What does the base sequence of a gene determine ?
The amino acid sequence in a polypeptide chain
What is known as a degenerate code ?
When more than one triplet can code for the same amino acid.
Describe the structure of tRNA and function of tRNA
Structure:
- Single stranded
- Folded to make a clover leaf shape, shape held in place via hydrogen bonds
Function:
- To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create polypeptide chain
- Specific amino acids attach to specific tRNA binding sites which is determined via the anti codon on tRNA
What is meant by an anti-codon?
Three bases which are found on tRNA which are complimentary to mRNA
Why are degenerate codes advantageous?
Some single base mutations may still code for the same amino acid.
What are start and stop codons?
Some codes do not code for specific amino acids however they code for the start or stop of the amino acid.
What is meant by non-overlapping
Each triplet is read separately in threes.
Give three differences between RNA and DNA
DNA contains deoxyribose , RNA contains Ribose
DNA is double stranded forming a double helix, RNA is single stranded
DNA contains thymine whilst RNA contains uracil
Give three differences between the process of DNA replication and Transcription
- DNA replication uses DNA nucleotides, transcription uses RNA nucleotides
- Replication uses DNA polymerase, transcription uses RNA polymerase
- Transcription copies only the template DNA strand, replication copies both strands.
Describe the process of Transcription
1 - DNA helicase binds to non coding region of DNA and breaks the hydrogen bonds between the two strands of DNA
2 - Template strand of DNA is exposed
3 - RNA then moves along the template strand and adds complementary nucleotides one at a time.
4 - RNA polymerase reaches the end of the anti sense strand and it detaches , mRNA then leaves via the nuclear pore and goes to ribosome.
Describe the process of translation
- Modified mRNA molecule attaches to ribosome in the cytoplasm
- tRNA carries amino acid
- tRNA molecule with the complimentary anti codon is attracted to complimentary codons in mRNA and hydrogen bonds form between them
- tRNA brings correct amino acid and peptide bonds are created between the amino acids
- Peptide bond created via condensation reaction
- tRNA is released from ribosome when it reaches stop codon
Where does this new polypeptide go to get modified
The golgi apparatus
What are gene mutations
- A change in the DNA base sequence at a single location
Explain a substitution mutation
- Amino acid in polypeptide is altered.
- mRNA transcribed contains a different codon
- Codons code for a different amino acid therefore produces a different polypeptide
- Polypeptide folds in a different shape therefore functioning protein not made
How does sickle cell anemia happen?
One single substituion of an amino acid which changes one amino acid in Haemoglobin
What is a deletion mutation?
- A base is deleted from DNA, frame shift occurs
- All mRNA codons are different
- When polypeptide chain is formed, all amino acids are changed and one is completely missing
-Polypeptide is folded in the wrong way and a functioning protein is not made
What are insertion mutations?
When a new nucleotide is added into the base sequence.
Explain insertion mutations
- Changes the amino acid which would have been coded for the original triplet of bases.
- Has knock on effect for other base triplets which causes a frame shift
