2.1 Structure of RNA and DNA Flashcards
Describe the basic function of DNA and RNA in all living cells
DNA: Holds genetic information which codes for polypeptides (proteins)
RNA: Transfers genetic information from DNA to ribosomes
Name the types of molecules from which a ribosome is made
RNA and Proteins
Draw (use ur imagination) a nucelotide
Phosphate group(circular)
Pentose-either deoxyribose or ribose- (pentagonal shape)
Nitrogenous base (Rectangle)
What is the monomer that makes up DNA
A nucleotide
What are the 4 nitrogenous bases in DNA
Guanine
Cytosine
Adenine
Thymine
What is the polymer form of a nucelotide
Polynucelotide
Describe how nucleotides join together to form polynucleotides (3)
- Condensation reactions, removing water molecules
● Between phosphate group of one nucleotide and deoxyribose / ribose of another
● Forming phosphodiester bonds
How is the polynucelotide held together
Strong covalent bonds called phosphodiester bonds
How are the DNA polymer pairs joined together
Hydrogen bonds between the Nitrogenous bases
This is how the double helix strcutre is created as the two chains twist
What is the only condition through which hydrogen bonds form in polynucelotides
They can only form between complimentary base pairs
Cytosine—Guanine
Adenosine–Thymine
Guanine—Cytosine
Thymine–Adenine
Number of ‘-‘ represent the number of h bond bwteen the bases
How does the structure of DNA relate to its function (7)
● Two strands → both can act as templates for semi-conservative replication
● Hydrogen bonds between bases are weak → strands can be separated for replication
● Complementary base pairing → accurate replication
● Many hydrogen bonds between bases → stable / strong molecule
● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
● Long molecule → store lots of genetic information (that codes for polypeptides)
● Double helix (coiled) → compact
Why did many scientists initially doubt that DNA carried the genetic code
DNA was relatively simple- Chemically simple molecules with few components
What is RNA (3)
*A polymer of a nucleotide formed of a:
Ribose
Nitrogenous base
Phosphate group
*Relatively short
*Single Stranded
Name the 4 nitrogenous bases in RNA
Adenine
Uracil
Guanine
Cytosine
What is the function of RNA
To copy and transfer the genetic code from the DNA in the nucleus to the ribosomes
What are the three types of RNA
mRNA-Messenger
tRNA-Transfer
rRNA-Ribosomal
What is mRNA
A copy of a gene from DNA
Created in the nucleus
What is the function of mRNA
Messenger
To carry a copy of the genetic code of one gene to a ribosome in the cytoplasm
Why is the function of mRNA important
DNA is too large to leave the nucleus and would be at risk of being damaged by enzymes —-> therefore destroying the genetic code permanently
Why is mRNA short
It is the length of one gene so it can therefore leave the nucleus
Why is mRNA short lived
It is only needed temporarily to help create a protein —> therefore by the time an enzyme breaks it down it would have already carried out its function
What is a codon
Three bases in a gene that code for specific amino acids
Where is tRNA found
in the cytoplasm
What is the structure of tRNA
Single stranded but folded to create a shape that looks like a clover leaf that is held in place by H bonds
What is the function of tRNA
To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create the polypeptide chin
Do random amino acids bind to random tRNA (3)
- No
- Specific amino acids bind to specific tRNA’s
- This is determined by the three bases found in the tRNA
How are mRNA and tRNA similar(codon-anticodon)
The three bases found in the tRNA are complimemtary to mRNA and these are called anti codon
What is the function of rRNA
To combine with proteins to make ribosomes
What are the differences between the DNA and RNA monomers
- DNA contains the base Thymine whereas RNA has Uracil instead of Thymine
- DNA contains the pentose suagr deoxyribose whilst RNA contains Ribose
What are the two differences between the polymers of DNA and RNA
- DNA is much longer as it contains 23,000 genes whereas RNA is shorter as it only contains 1
- DNA is double stranded whilst RNA is single stranded
Describe the structure of mRNA (5)
- Polymer of nucleotides
- Each nucelotide formed from ribose, a phosphate group and a nitrogen base containing organic base
- Bases are Uracil Adenine Cytosine Guanine
- Phosphodiester bonds join adjacent nucelotides
- Single helix
Describe the structure of DNA (6)
- Polymer of nucelotide
- Each nucelotide formed from deoxyribose, a phosphate group and a nitrogen containing organic base
- Phosphodiester bonds join adjacent nucelotides
- 2 polynucelotide chains held together by hydrogen bonds
- Between specific complimentary base pairs- Adenine/Thymine Cytosine/Guanine
- Double helix
Compare and contrast the structure of DNA and mRNA (5)
-DNA Pentose sugar is deoxyribose whereas in mRNA the pentose sugar is ribose
-DNA has the base thymine whereas in mRNA the base has no thymine but has Uracil instead
-DNA is double stranded whilst mRNA is single stranded
-DNA is longer (more nucelotides) mRNA is shorter (less nucelotides)
-DNA has hydrogen bonding mRNA does not
Which Nitrogenous bases are Purine
Adenine and Guanine
They both have two rings
Guanine has a double bond to O
Which Nitrogenous bases are pyrimidine
Thymine Cytosine and Uracil
Has one ring
Why can Adenine and Cytosine not bond
Adenine would form 2 hydrogen bonds whereas Cytosine would form 3 hydrogen bonds
What is the differnece between Deoxyribose and Ribose
Deoxyribose chemical formula-C5 H10 O4
Ribose has the same but one more oxygen
Strcture of Deoxyribose is more stable so it has a sotrnger covalent bonds as the C3 bond will be bonded directly oto the phosphate group
How are polynucleotides formed
When DNA contains a second antiparallel chain that runs in the opposite direction
E.g. 5’ prime and 3’ prime end
Why is DNA stable
- The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- Hydrogen bonds link the organic base pairs forming bridges
Suggest how you can use incomplete information about the frequency of
bases on DNA strands to find the frequency of other bases
- % of adenine in strand 1 = % of thymine in strand 2 (and vice versa)
- % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa)
Because of specific complementary base pairing between 2 strands
