**1.4 DNA + protein synthesis** Flashcards
What are nucleic acids?
- ‘Information of cells’.
- This determines sequence of amino acids in each protein a cell can produce.
What are the two types of nucleic acids?
- DNA (deoxyribonucleic acid).
- RNA ( ribonucleic acid).
What are nucleic acids formed from?
- Nucelotides.
What is a nucleotide?
- Monomer from which nucleic acids are formed.
What are nucleotides comprised of?
- A pentose, a phosphate group + a purine or pyrimidine base.
What type of pentose is used in DNA and RNA?
- DNA - deoxyribose.
- RNA - ribose.
What type of base is a single-ringed base?
- Pyrimidine.
What type of base is a double-ringed base?
- Purine.
What are the purine bases used in DNA and RNA?
- DNA - either adenine or guanine.
- RNA - either adenine or guanine.
What are the pyrimidine bases used in DNA and RNA?
- DNA - either cytosine or thymine.
- RNA - either cytosine or uracil.
How do phosphoric acid, pentose sugars + nitrogenous bases combine to form a nucleotide?
- Condensation reaction.
How can two nucleotides be joined together?
- Condensation reaction.
- Catalysed by an enzyme DNA polymerase.
What is DNA polymerase?
- Enzyme that catalyses formation of phosphodiester bond between two nucleotides.
What does the condensation reaction of two nucleotides result in?
- Formation of a covalent bond called a phosphodiester bond between two nucleotides.
What is a phosphodiester bond?
- Covalent bond between 2 nucleotides.
What is called when large numbers of nucleotides condense together?
- Nucleic acids/ polynucleotides.
What is the structure of a nucleic acid/ polynucleotide?
- Very long, thread-like macromolecule.
- Sugar-phosphate backbone w/ bases attached to each sugar.
What is the backbone of a nucleic acid/ polynucleotide made of?
- Alternating sugar + phosphate molecules.
Are RNA molecules generally long or short?
- Relatively short.
- Between 100 and 1000s of nucleotides long.
Which base never appears in RNA?
- Thymine.
What are the three functional types of RNA?
- Messenger RNA (mRNA).
- Transfer RNA (tRNA).
- Ribosomal RNA.
What is the function of mRNA?
- Carries a copy of a single gene to cell’s ribosomes.
What is the function of tRNA?
- Carries individual amino acids to ribosomes during protein synthesis.
What is the function of ribosomal RNA?
- Forms part of the sub-units of ribosomes.
Are DNA molecules generally long or short in length?
- Extremely long strands, several million nucleotides in length.
Which base never appears in DNA?
- Uracil.
How many polynucleotide strands are found in DNA, how are they held together and what is the structure?
- 2 strands.
- Hydrogen bonds between complementary bases.
- Double helix structure.
What are the complementary base pairings in DNA?
- Adenine w/ thymine.
- Cytosine w/ guanine.
What is complementary base pairing?
- 2 antiparallel polynucleotide chains are held together by hydrogen bonds between the bases adenine + thymine or cytosine + guanine.
What are the three reasons that complementary base pairing important?
- Stability of DNA double helix (lots of hydrogen bonds).
- Genetic info can be transferred from DNA to RNA (mRNA).
- The way amino acids are assembled into polypeptides in cytoplasm.
What makes two DNA strands antiparallel?
- The sugar-phosphate backbones point in different directions.
How many hydrogen bonds form between A+T bases?
- 2.
How many hydrogen bonds form between C+G bases?
- 3.
What is DNA replication?
- Process of exactly copying DNA to go into a daughter cell.
How is DNA ‘un-zipped’ for DNA replication?
- Replication sites open at either end DNA double helix.
- Enzyme DNA helicase is used.
- Unwinds helix + breaks H-bonds.
- Replication sites join up.
What are the 5 steps of DNA replication?
- DNA ‘un-zips’ + H-bonds break.
- Single strand acts as template.
- Free nucleotides w/ complementary bases slot in + held w/ H-bonds.
- Sugar-phosphate backbone is formed through condensation reactions (DNA polymerase)
- Replicated (daughter) DNA molecules each rewind into double helix.
What is semi-conservative replication?
- 2 copies of DNA molecule made + both ‘parent’ strands remain intact + act as templates for formation of new complementary strands.
Which enzyme breaks H-bonds + unwinds DNA double helix?
- DNA helicase.
Which enzyme links nucleotides in developing strands?
- DNA polymerase.
What is the enzyme that joins DNA segments together?
- DNA ligase.
What other role does DNA polymerase have?
- ‘proof-reading’ + replace any ‘mistakes’ in bases.
What is a gene?
- Sequence of DNA nucleotide bases that encodes the sequence of amino acids in functional polypeptide.
Can genes vary in length?
- Yes.
How many amino acids are there?
- 20.
What is genetic code?
- Combination of 3 bases that encodes an individual amino acid.
- This is universal.
What type of code is genetic code?
- Degenerate code.
What is degenerate code?
- Sets of three nucleotides or codons can code for the same amino acid during protein synthesis.
What is a codon?
- Nucleotide base triplet on mRNA that encodes a single amino acid.
What is an antisense strand?
- Polynucleotide chain in a DNA molecule that is always used in protein synthesis to determine order of amino acids in a polypeptide.
- Strand that is transcribed.
Genetic code is non-overlapping, what does this mean?
- Each nucleotide base forms part of only one base triplet.
How many directions is DNA base sequence read in?
- One.
What are the 3 stages of protein synthesis?
- One - Transcription.
- Two - Activation of amino acids.
- Three - Translation.
What is transcription?
- Process of DNA nucleotide base sequence of gene being copied into RNA nucleotide base sequence in a molecule of mRNA.
How is the process of transcription carried out?
- DNA double helix unwinds.
- One strand of DNA acts as template for mRNA.
- Free RNA nucleotides pair up w/ nucleotides on antiscense strand.
- Complementary base paring –> A+U and C+G.
- RNA polymerase catalyses phosphodiester bonds between RNA nucleotides forming mRNA.
- Through nuclear pores in nuclear membrane + travel to ribosomes.
- Transcription of gene.
How is the process of activation of amino acids carried out?
- Amino acids combine w/ tRNA (transfer RNA) in cytoplasm.
- Different tRNA for all amino acids.
- Anticodon is complementary to codon of mRNA.
How is the process of translation carried out?
- Protein chain assembled one aa at a time.
- Ribosomes move to mRNA + start ‘reading’ it.
- Complementary codons/anticodons held by H-bonds.
- Amino acids joined by peptide linkages.
What are introns?
- DNA base sequences within a gene that do not code for amino acid sequence of a polypeptide.
- Although copied to RNA during DNA transcription, edited out of mRNA before it leaves nucleus.
What are exons?
- DNA base sequences within a gene that code for the amino acid sequence of a polypeptide.
What is gene mutation?
- Random + unpredictable change in number or sequence of bases in a single gene.
What are the 3 possible types of gene mutation?
- Base deletion.
- Base insertion.
- Base substitution.
What is a point mutation?
- A gene mutation involving deletion, insertion or substitution of a single base.
What is an example of point mutation?
- Sickle cell anaemia.
What amino acid is affected by the point mutation in sickle cell anemia?
- AA sequence of part of respiratory pigment haemoglobin.
What type of point mutation is sick cell anaemia?
- Substitution.
- A instead of T in one base triplet.
What happens to the haemoglobin is sickle cell anaemia?
- Haemoglobin tends to clump together + form long fibres.
- RBCs form sickle shape.
What is the affect of sickle cell anaemia?
- Oxygen transport is less efficient + cells may block smaller capillaries.
Anti-sense strand meaning?
- Strand of DNA used as complementary template for mRNA synthesis.
Coding DNA meaning?
- Section of DNA which codes for proteins.
Degenerate (genetic code) meaning?
- Some amino acids can be coded for by multiple different codons.
Deletion mutation meaning?
- Nucleotides not incorporated into chain - frameshift mutation.
Gene meaning?
- Sequence of bases on DNA molecule coding for sequence of amino acids on a polypeptide chain.
Gene mutation meaning?
- Change to at least one nucleotide bases or arrangements of bases. Occur spontaneously + may be a harmful or positive change to genotype.
Insertion mutation meaning?
- Extra nucleotides incorporated into chain.
- Frameshift mutation.
Function of ligase?
- Joins Okazaki fragments together with phosphodiester bonds.
