Nucleotides, DNA replication and Protein Synthesis Flashcards
Name the components of a nucleotide?
Phosphate group, nitrogenous base, covalent bond, pentose sugar and an ester bond
What are nucleotides?
Monomers of larger polymers nucleic acids
What does DNA stand for?
Deoxyribonucleic acid
What does RNA stand for?
Ribonucleic acid
What are features of DNA?
Double stranded, its pentose sugar is deoxyribose, its nitrogenous bases are A, T, C and G, and it is very long
What are the features of RNA?
Single strand, its pentose sugar is ribose, its nitrogenous bases are A, U, C and G, it is very short (one gene long)
What are the differences between DNA and RNA?
DNA stays in the cell, RNA goes out of the cell. DNA is very long, RNA is very short. DNA uses thymine, RNA uses uracil. DNA is in a double helix, RNA is in a single helix, DNA is more stable than RNA
What is a purine molecule? What nitrogenous bases are purines?
A molecule with two rings, guanine and adenine
What is a pyrimidine molecule? What nitrogenous bases are pyrimidines?
A molecule with a single ring, cytosine, thymine and uracil
How many rings are there in complementary base pairing?
3 rings, because purine have 2 rings and pyrimidines have 1 ring
What are the roles of nucleotides?
Synthesis and repair of nucleic acids, metabolic functions such as ATP
What reaction bonds together nucleotides?
Condensation reactions
Where is the phosphodiester bond on a nucleotide?
5th Carbon on the phosphate group and 3rd carbon on the hydroxyl group
What is a phosphodiester bond?
A covalent bond between 2 pentose sugars
What bonds are between the complementary base pairs?
Hydrogen bonds
How many hydrogen bonds are between the base pairs?
2 hydrogen bonds for A-T and 3 hydrogen bonds for C-G
What does ‘anti-parallel’ mean in context to DNA strands?
On the sugar phosphate backbone, one strand is from carbon 3 to carbon 5 but the other strand is the opposite: carbon 5 to carbon 3
Why is complementary base pairing important?
Ensures same distance between pairs, ensures faithful replication, maintains high fidelity of replication- and is bi-directional
What is transcription?
The process of turning DNA into RNA
Where does transcription occur and why?
The nucleus because DNA is too big to fit outside of the nucleus
What is translation?
The process of going from mRNA to proteins
Where does translation occur?
Ribosomes
What is protein synthesis?
Transcription then translation
What are the three types of RNA?
mRNA, tRNA and rRNA
How is mRNA made?
On the template strand complementary to the DNA coding strand with uracil instead of thymine
What is the function of mRNA?
To carry information out of the nucleus
What is tRNA?
Transfer RNA: attaches amino acids via peptide bonds to form poly peptides
Name the features of tRNA
Clover shaped, single stranded, folded, anticodon at the end to bind to mRNA at its codon via complementary base pairing
What enzyme does transcription use?
RNA polymerase
What is the RNA transcribed from the DNA templates called?
A gene
List the steps of transcription
1- RNA polymerase separates the DNA strands partially
2- RNA nucleotides align opposite on the coding strand due to complementary base pairing
3- RNA polymerase bind the nucleotides covalently, which forms phosphodiester bonds
4- The gene is synthesised so RNA polymerase detaches from the DNA molecule and the double helix reforms
Which direction is RNA formed?
RNA polymerase ‘walks’ in a 3’ to 5’ direction but mRNA is formed at a 5’ to 3’ direction
In transcription, what is initiation?
When the RNA polymerase binds to the DNA at a region called the promoter region
Describe transcription’s initiation
RNA polymerase binds to a promoter region, then the DNA behinds to partially unwind in a 3’ to 5’ direction
What is transcription’s elongation?
When the RNA polymerase begins to move along the DNA template strand to catalyse the formation of phosphodiester bonds to join the nucleotides to the strand of mRNA
What is transcription’s termination?
When the RNA polymerase detaches from a DNA strand and the synthesised mRNA detaches so the double helix reforms (stop codon)
Where are ribosomes found and how does that effect their function?
Free in cytoplasm (proteins for inside the cell), on rough endoplasmic reticulum (proteins for export outside of cell)
What subunits do ribosomes consist of?
Large and small
What are ribosome subunits made of?
Proteins and rRNA
What is the role of peptidyl transferase in ribosomes?
Catalyse formation of peptide bonds between amino acids
What does translation depend on?
Complementary base pairing between the mRNA codons and the tRNA anticodons
List the steps of translation
1- ribosome binds to the mRNA and moves along the molecule from 5’-3’
2- tRNA with the anticodon to match the start codon is needed to start translation
3- mRNA reads one codon at a time
4- ribosomes catalyse formation of peptide bonds between adjacent amino acids via condensation reactions
5- this continues until the ribosome reaches a stop codon
6- the polypeptide is released
Which 2 amino acids contain sulfur
Cysteine and methionine
Why is the amino acid sequence important?
Defines shape of protein
What are the key points of DNA replication?
Original strand is called the template strand, strand being complementary base paired is coding strand, one strand is newly synthesised, this is called semi-conservative
What is DNA replication in terms of mitosis?
Anaphase
Name the steps of DNA replication
1- helicase unwinds and unzips DNA strands, so each strand is a template
2- DNA polymerase binds to primer and joins DNA nucleotides from 3’ to 5’
3- the leading strand continuously synthesised due to its 5’ to 3’ formation
4- however the lagging strand is made 5’ to 3’ so is made in Okazaki fragments
5- DNA ligase joins strands together which makes 2 new molecules of DNA
What are the enzymes used in DNA replication?
Helicase, DNA polymerase and DNA ligase
Why is DNA replication semi-conservative?
Because each DNA molecule is made of one old strand and one new strand
What are the 2 strands in DNA replication
Leading strand and lagging strand
What are Okazaki fragments?
A fragment of DNA on the lagging strand that is made 5’ to 3’
What is the role of helicase in DNA replication?
Unwinds and unzips the DNA molecule into 2 template strands that run anti-parallel to each other (catalysing breakage of hydrogen bonds)
What is the role of DNA polymerase in DNA replication
Synthesises new DNA molecules from 2 template strands by forming phosphodiester bonds between nucleotides
What is proof for the semi-conservative theory?
Meselson and Stahl experiment with ‘heavy’ and ‘light’ nitrogen
