C1- Nucleic acids and their functions. Flashcards
1
Q
What are nucleic acids?
A
Polymers made up of monomers called nucleotides. The polymer is referred to as a polynucleotide.
2
Q
How are nucleotides combined?
A
By a condensation reaction.
3
Q
What are the three components of nucleotides?
A
- A phosphate group
- A pentose sugar
- An organic base/ nitrogenous base
4
Q
What pentose sugar is in in RNA and what pentose sugar is in DNA?
A
RNA- ribose
DNA- deoxyribose
5
Q
Name the two groups of organic bases and the bases in each.
A
- purine bases... adenine guanine - pyrimidine bases... thymine cytosine uracil
6
Q
What molecule makes energy available?
A
ATP- adenosine triphosphate
7
Q
What is ATP composed of?
A
- the base adenine
- the sugar ribose
- three phosphate groups
8
Q
When a molecule of ATP is hydrolysed how much energy is released?
A
30.6 KJmol^-1
9
Q
What enzyme hydrolyses ATP to release energy?
A
ATPase
10
Q
What is the addition of a phosphate to ADP called?
A
Phosphorylation.
11
Q
What is an endergonic reaction?
A
A reaction that requires the input of energy.
12
Q
What enzyme allows phosphorylation to occur and what type of reaction is this?
A
ATP synthetase
This is a condensation reaction.
13
Q
What are the advantages of using ATP compared to glucose?
A
- The hydrolysis of ATP in a single reaction, glucose taken longer to be broken down as there are many intermediate stages.
- Only one enzyme is required to release energy from ATP.
- ATP releases energy in small amounts where it is required, glucose releases it in large amounts all at once.
- ATP provides a common source of energy for many different chemical reactions, this improves the efficiency and control of the cell.
14
Q
What activities require ATP?
A
- metabolic processes
- active transport
- movement
- nerve transmission
- secretion- the packaging and transport of secretory products into vesicles in cells
15
Q
Describe the structure of DNA.
A
Two polynucleotide strands wound around each other in a double helix. The strands are antiparallel to each other, one runs 5’ to 3’ and the other 3’ to 5’.
16
Q
What is the backbone of DNA?
A
The deoxyribose sugar and the phosphate group.
17
Q
Describe which bases pair together and what the name for this is.
A
They are known as complimentary base pairs.
- Adenine and Thymine- have two hydrogen bonds between them
- Cytosine and Guanine- have three hydrogen bonds between them
18
Q
What maintains the double helix shape of DNA?
A
The hydrogen bonds.
19
Q
Why is DNA suitable for its functions?
A
- very stable so its information remains essentially unchanged from generation to generation.
- large so carries a lot of genetic information
- the two strands can separate as held together by hydrogen bonds
- the base pairs are protected by the deoxyribose phosphate backbone.
20
Q
Describe the structure of RNA.
A
- single stranded polynucleotide
- contains the pentose sugar ribose
- contains the bases adenine, guanine, cytosine and uracil (not thymine)
21
Q
Name the three types of RNA.
A
Messenger RNA
Ribosomal RNA
Transfer RNA
22
Q
What is the function of messenger RNA (mRNA) in protein synthesis?
A
- synthesised in the nucleus
- carries genetic code from the DNA to ribosomes in the cytoplasm
- different mRNA have different lengths depending on the genes they’re synthesised from.
23
Q
What is the function of ribosomal RNA (rRNA) in protein synthesis?
A
- found in cytoplasm
- comprises large complex molecules
- ribosomes are made of rRNA and protein- they’re the site of translation.
24
Q
What is the function of transfer RNA (tRNA) in protein synthesis?
A
- small
- single stranded, but folded like a clover leaf
- has bases that form complimentary pairs
- 3’ end has the sequence CCA, where a specific amino acid the molecule carries is attached
- has a sequence of three more bases called the anticodon
- transports specific amino acids to the ribosomes in protein synthesis.
25
What are the two roles of DNA?
Replication and protein synthesis.
26
Name a describe the three types of DNA replication that were thought to be a possibility.
- Conservative replication- parental double helix remains in tact/ is conserved and a whole new helix is made.
- Semi-conservative replication- the parental double helix separates into two strands, each acting as a template for the synthesis of a new strand.
- Dispersive replication- the two new double helices contain fragments from both strands.
27
What is meant by triplet code?
The polynucleotide strand always has three times the number of bases than amino acids it codes for.
28
Describe the characteristics of genetic code.
- three bases encode each amino acid so it is a triplet code
- more than one triplet can encode each amino acid so the code is described as 'degenerate' or 'redundant'
- the code is punctuated as stop codons mark the end of a portion to be translated.
- universal code
- the code is non-overlapping, each base occurs in only one triplet
29
Describe the stages of semi-conservative replication.
- hydrogen bonds break that hold the base pairs together.
- DNA unwinds catalysed by the enzyme helicase so that the two strands separate.
- The enzyme DNA polymerase catalyses the condensation reaction between the DNA strand that acts as a template and free nucleotides joining them to their complimentary bases
30
Describe how the RNA used to synthesise polypeptides in prokaryotes differs from that in eukaryotes.
- In prokaryotes the RNA is messenger RNA (mRNA).
- In eukaryotes the initial RNA code is much longer than the final RNA and is referred to as pre-messenger RNA (pre-mRNA). It contains sequences of bases that need to be removed called introns that do not translate into proteins. The sections of RNA left are called exons.
31
How are introns cut out of RNA and the remaining exons joined together?
- Introns are cut out using endonucleases.
| - Exons are spliced together with ligases.
32
Name the two stages of protein synthesis and give a brief description of each.
- Transcription- one strand of DNA acts as the template for mRNA (a complementary section of part of the DNA sequence). Occurs in the nucleus.
- Translation- mRNA molecules act as a template for tRNA molecules to attach. The amino acids they carry form a polypeptide.
33
What occurs during transcription?
- DNA helicase breaks the hydrogen bonds in DNA, so the two strands separate and unwind exposing the nucleotide bases.
- RNA polymerase binds to the template strand of DNA at the beginning of the sequence to be copied.
- Free RNA nucleotides align opposite the template strand based on their complementary relationships.
- RNA polymerase moves along the DNA forming bonds between RNA nucleotides to grow the RNA strand, hence mRNA is synthesised.
- RNA separates from the template strand when it reaches a stop signal.
- The DNA rewinds into its double helix behind the formation of the RNA.
34
What occurs during translation?
- Initiation- a ribosome attaches to the start codon on the mRNA molecule.
- The first tRNA with an anticodon complimentary to that of the first codon on the mRNA, attaches to the ribosome. Three bases of the codon on the mRNA, bond to the three complimentary bases of the anticodon on the tRNA with hydrogen bonds. This occurs two at a time as there are two attachment sites for tRNA.
- Elongation- a ribosomal enzyme catalyses the formation of a peptide bond between two sufficiently close amino acids.
- tRNA leaves the ribosomes to bind to another copy of its specific amino acid, leaving its attachment site vacant for another tRNA to bind to.
- The ribosome moves one codon along the mRNA strand each time tRNA leaves.
- Termination- the sequence repeats until a stop codon is reached.
- The ribosome- mRNA- polypeptide complex separates.
35
Describe the structure of ribosomes.
Made of two subunits...
- larger subunit has two sites for the attachment of tRNA molecules.
- smaller subunit binds to mRNA.
36
If DNA has the triplet GAG what code will the mRNA codon have and the tRNA anticodon have?
mRNA codon- CUC
| tRNA anticodon- GAG
37
What is amino acid activation?
When energy from ATP is used to attach an amino acid to tRNA.
38
What is the one gene- one polypeptide hypothesis and how did it come about?
- initially was the one gene- one enzyme hypothesis.
- then became the one gene- protein hypothesis.
- finally the one gene- one polypeptide hypothesis which states a gene is a sequence of DNA bases that codes for a polypeptide.
39
What is the modification of a polypeptide called and where does it occur?
It is called post- translational modification and occurs in the Golgi body.
