Viruses contain either DNA OR RNA
A virus that is composed not of DNA but of RNA is called a
Viroids are infectious agents without protein
Prions –are infectious agents with both DNA and RNA
Adenine and guanine are
pyrimidines
purines
A nucleoside is formed when a base is linked to the WHAT carbon of a deoxyribose (or ribose) molecule
1'
2'
3'
4'
dCMP and dAMP are examples of nucleotides nucleosides proteins nucleic acid( nucleotides, nucleosides, proteins, nucleic acid )
In DNA and RNA, nucleotides are linked by phosphodiester bonds between the ❌ and 3′ carbons
In all prokaryotes and eukaryotes DNA is double-stranded
Guanine and Cytosine form a base-pair held together by hydrogen bonds. Adenine and Thymine form a base-pair held together by hydrogen bonds.
Most or all cellular DNA is A-DNA
Z-DNA is left handed and A-DNA is right handed
Underwinding generates supercoils Overwinding generates supercoils
Single stranded DNA absorbs more UV than double stranded DNA
UV absorbance rises as DNA denatures is known as the
Tm (The temperature needed to denature 50% of the DNA molecules in a sample) is increased in DNA with high content of AT base-pairs
What are three key structural differences between DNA and RNA?
RNA has ribose instead of deoxyribose.
RNA has deoxyribose instead of ribose
RNA contains adenine, cytosine and guanine (like DNA) but has Uracil (U) instead of thymine.
RNA contains adenine, cytosine and guanine (like DNA) but has thymine (T) instead of uracil
RNA is usually double stranded
RNA is usually single stranded
Plasmids carry non-essential genes, e.g. for antibiotic resistance
Bacterial genomes usually consist of a single, linear chromosome made of double-stranded DNA
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(Length of DNA/ Length of structure DNA packed into) is known as the
By mass, the composition of a chromosome at mitosis is approximately
1/2 DNA and 1/2 histone proteins
1/3 DNA and 2/3 histone proteins
1/3 DNA, 1/3 histone proteins and 1/3 non histone proteins
1/2 DNA. 1/4 histone proteins and 1/4 non histone proteins
20% of amino acids are arginine or lysine
is a ring-shaped protein that can anchor the ends of a loop of DNA
is an enzyme that can remove supercoils from DNA
Acetylation removes positive charge from side-chain and so ❌ interaction between histones and negatively-charged DNA
Eukaryotic chromosomes have 1 origin of replication
In bacterial replication, replication begins at a single AT-rich origin and is bidirectional
What enzyme carries out transcriptase?
Maltase
DNA transcriptase
RNA
RNA polymerase
DNA helicase
To synthesise RNA, RNA polymerases require:
A primer
A double stranded template DNA molecule that Includes a promoter sequence
All four nucleoside triphosphates
RNA polymerase binds to the promoter in the stage
RNA polymerase dissociates from DNA releasing the new RNA molecule in the stage
RNA polymerase moves along the DNA molecule synthesising an RNA copy in the stage
A sequence is a sequence of DNA having similar structure and function in different organisms.
The holoenzyme carries out elongation but not initiation
Eukaryotic promoters differ from those in bacteria
RNA polymerase I ll lll( I, ll, lll ) - synthesises rRNA RNA polymerase I ll lll( I, ll, lll ) - synthesises tRNA RNA polymerase I ll lll( I, ll, lll ) - synthesises mRNA
RNA polymerase II produces a 1° transcript (aka pre-mRNA) which is processed in the nucleus to form mRNA. The main processing reactions are
Initiation
RNA splicing
DNA splicing
Cleavage and polyadenylation
Capping
Druining
Promoters recognised by RNA polymerase II usually consists of a core promoter that may include a TATA TAAT ATAT ATTA( TATA, TAAT, ATAT, ATTA ) box
RNA polymerases and DNA polymerases share the same mechanism.
By mass, ribosomes have about a 1:2 ratio of rRNA to protein
The size of ribosomes is measured in Svedbergs (S) - sedimentation rate during centrifugation.
The small subunit on a ribosome catalyses peptide bond formation, the large subunit binds the mRNA being translated
mRNA is read from
5' to 3'
3' to 5'
The small (30S) ribosome subunit binds to the ribosome binding site on the mRNA in E.Coli
There are several ribosome binding sites on mRNA in eukaryotes
A sequence has ❌ possible reading frames depending on where translation starts from
The region between an initiation codon (AUG) and a termination codon is an“open-reading frame”
How do amino acids recognise codons? Adaptor molecules deliver amino acids to the appropriate codons. These adaptors are transfer RNAs
How long are tRNAs?
Large: 220-293 nucleotides long
Small: 50-73 nucleotides long
Small: 73-90 nucleotides long
Large: 320-393 nucleotides long
All tRNAs have an anticodon
All tRNAs have the sequence GCA at their 3' end.
the ability of some bases at 5' end of anticodon to pair with more than one base at 3' end of codon is known as the
The enzymes that link tRNAs to amino acids are called
aminoakyl-tRNA synthetases.
aminoacyl-tRNA synthetases.
aminoacyl-rRNA synthetases.
aminoakyl-rRNA synthetases.
The classic example of inducible genes are the three genes required for utilisation of lactose by E. coli. These are:
Lac Z gene
Lac B gene
Lac A gene
Lac Y gene
Lac T gene
The is the binding site for lac repressor protein.
The Lac gene encodes the Lac repressor protein.
Transcription of the genes of the lac operon is repressed by the lac protein
When lactose is absent, the lac repressor protein binds to the promoter
When the lac repressor protein is bound to the operator, RNA polymerase can still bind to the promoter but cannot initiate transcription.
When lactose is present some is converted into an isomer called .
Allolactose binds to the lac repressor protein inducing a conformational change so that lac repressor cannot bind to operator.
Lactose breakdown is only necessary if glucose is not available. Therefore when both lactose and glucose are present in environment, lac operon genes only transcribed weakly. This effect is called Repression
Removal of catabolite repression requires:
The Catabolite Activator Protein (CAP)
cAMP
ATP
Lac i gene
When glucose conc’ is high the cAMP conc’ is low
Monosaccharides Polysaccharides Oligosaccharides( Monosaccharides, Polysaccharides, Oligosaccharides ) are colourless, crystalline solids, water soluble and most are sweet tasting.
In general, a molecule with n chiral centres can have 2 1 3 4( 2, 1, 3, 4 )n stereoisomers
: each of two isomers with different configurations of atoms about one of several asymmetric carbon atoms present
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