DNA, RNA And Proteins Flashcards
What is the role of macromolecules?
If organic (carbon-containing) they are crucial for most biological functions e.g. nucleic acids (DNA + RNA), proteins, carbohydrates + lipids
What is the function of nucleic acids such as DNA and RNA?
Information storage + transmission
What are the functions of proteins?
Enzymatic catalysis Antibodies Hormonal signalling Structural proteins Contractile proteins Gas transport
What is the function of carbohydrates?
Energy source
What are the functions of lipids?
Energy source
Membrane components
Hormonal signalling
Why are DNA, RNA and proteins special?
All molecules conform to physical + chemical laws but through their complex behaviour, nucleic acids + the proteins they encode display properties appearing to transcend those laws - ‘life’
E.G. proteins are cellular components with precise structures defined by sequence info - many are highly specific catalysts (enzymes) that allow the large no. of chemical reactions necessary for life to occur simultaneously in cells
What are Deoxyribose Nucleic Acid (DNA) and Ribose Nucleic Acid (RNA) made up of?
Polymers of nucleotides
Nucleotides consist of a sugar (deoxyribose/ribose), phosphate + a variable ‘base’ which forms the sequence - in DNA this encodes AA sequences of proteins + RNA involved in translating this DNA code
What are proteins made up of?
Polymers of 20 different kinds of AAs
AAs form a sequence that determines the protein shape + thus, its function
How are nucleotides structured within DNA?
The 4 bases pair via H-bonds according to simple rules where A pairs with T (U in RNA) + G pairs with C
Nucleotides connected to sugar-phosphate backbone
The 2 DNA strands run in opposite directions
The molecular properties of DNA allow it to perform its 2 great functions. What are they?
- To control information on what proteins to make
2. To pass that information on to daughter cells
What is the structure of DNA?
Bases stack in centre of helix forming an uncharged core with H-bond donors/acceptors (recognised by proteins/drugs in sequence-specific manner)
-vely charged sugar-phosphate backbones not equally spaced forming major + minor grooves (relevant to protein/drug binding too)
Explain the central dogma of molecular biology.
Info in DNA conserved with high fidelity by DNA REPLICATION
During gene expression, info is passed from DNA to mRNA in TRANSCRIPTION
Info passes from mRNA to protein via TRANSLATION (3 bases = 1AA)
How does semi-conservative DNA replication occur?
Each strand acts as a sequence template for DNA synthesis leading to 2 DNA helices
Replication passes on exact sequence of bases to both daughter DNA helices but only 1 strand (1/2 the original DNA helix) is passed onto new helix hence the term ‘semi-conservative’
What is the mechanism of DNA replication?
Hydrolysis of nucleoside triphosphates provides energy for incorporation of each new nucleotide into DNA polymer
DNA polymerase can only go 5’ to 3’ direction so goes directly in leading strand and in short stretches (Okazaki fragments) in the lagging strand
What is the mechanism of transcription?
- RNA polymerase separates DNA helix + binds to template strand at the promoter
- RNA polymerase moves along strand 5’ to 3’ producing complementary RNA nucleotides
- RNA polymerase terminates at stop codon + complementary mRNA strand has been produced
What is the mechanism of translation?
- mRNA strand binds to small ribosomal subunit which is joined at start codon by first tRNA carrying AA methionine which binds to codon via anticodon
- Small + large ribosomal subunits interlock around mRNA strand
- A 2nd tRNA arrives at adjacent binding site of ribosome binding to the next mRNA codon via its anticodon
- 1st AA detaches from tRNA + joined to 2nd AA by a peptide bond
- Ribosome moves 1 codon further along mRNA where 1st tRNA detaches as another arrives
- Chain elongates until stop codon is reached + components separate
What is a ribosome?
A RNA enzyme/ribozyme made mostly of rRNA with its substrate being aminoacyl-tRNA + its template for protein synthesis (translation) being mRNA
What type of reactions do proteins not catalyse?
Their own synthesis
What is the structure of transfer RNA (tRNA)?
Complex cross-shaped structure formed by base-pairing between nucleotides
AA joined to RNA at 3’ end far from anticodon
What enzyme loads the correct amino acid onto each tRNA?
Aminoacyl tRNA synthetase
What is the structure of amino acids?
Amino + carboxyl group at opposing ends (both groups ionized at pH 7)
α-carbon atom
R side chain (20 different varieties)
How are peptide bonds formed?
Condensation reaction where H2O is removed from 2 AAs to form a planar amide bond (CO=NH) which is chemically very stable
What are the different types of amino acids? Give examples of each.
- Small: Gly, Ala
- Nucleophilic: Ser, Thr, Cys
- Hydrophobic: Val, Leu, Ile, Met, Pro
- Aromatic: Phe, Tyr, Trp
- Acidic: Asp, Glu
- Amide: Asn, Gln
- Basic: His, Lys, Arg
What are the 3 types of intramolecular forces?
- Electrostatic attractions
- Hydrogen (H) bonds
- Van der Waals/hydrophobic attractions
How are amino acids arranged in an α-helix?
Right-handed helical structure where each AA gives 100o turn in helix
NH group from 1 AA forms a H-bond with the CO group of the AA 4 residues earlier
How are ß-sheets formed?
ß-strands formed by AAs in an extended conformation -> H-bonds between adjacent ß-strands formed ß-sheets
What are the 2 types of ß-sheet?
Parallel: strands run in same direction
Antiparallel: strands run in opposite direction
What is a protein motif?
Super 2ndary structure where a set of 2ndary structure elements are found together in different proteins
Often have same function in different proteins e.g. DNA binding (not always the case)
What is a protein domain?
Structure within a protein that can fold + function independently of the rest of the polypeptide chain
Often found in multiple proteins + many proteins contain multiple domains
What are the levels of protein structure?
- Primary: AA sequence of polypeptide
- Secondary: arrangement of α-helices, ß-strands + loop regions
- Tertiary: overall shape when AA side chains included
- Quaternary: multiple polypeptide chains + non-polypeptide elements
Give a good example of a quaternary structure.
Haemoglobin (Hb) as it has 4 near-identical polypeptide chains + 4 haem groups
What is myoglobin similar to?
A single polypeptide chain of Hb with 1 haem
