DNA and genes Flashcards
what is the structure of nucleotides
-deoxyribose sugar
-nitrogenous organic base
-phosphate
-deoxyribose is H
- Ribose is OH
-DNA= deoxyribonucleic acid
-RNA= ribonucleic acid
what is complementary base pairing
4 different nucleotides in DNA
Adenine + Thymine
Cytosine + Guanine
A + G= purines
C + T= pyrimidines
Structure of DNA
Chains of nucleotides
Double stranded (double helix)
5’ to 3’ =strands are anti-parallel
Complimentary base pairing
A-T
G-C
what is the chemical structure of bacterial genomic DNA
-chemical structure= Strand of nucleotides- A, C, G, T
-’Free“ state= not enclosed by a nuclear membrane
-DNA present in the nucleoid (a dense region in the centre of the cytoplasm)= Some similarity to eukaryotic chromosome
what is the structure of bacterial genomes
-Normally 1 large, double-stranded DNA molecule (there are exceptions)
-generally circular= exception: Borrelia
-Wide variety of sizes between species= One of the smallest bacterial genome sizes: ca. 600 000 bp Mycoplasma spp.
-orten additional circular DNA molecules (plasmids, phages etc)= In cytoplasm but separate from chromosome
what are chromosomes
harbors genes encoding functions essential under all conditions
what are the introns like in procaryotes
introns very rare, very little repetitive DNA
what are the introns like in eucrayotes
extensive introns, extensive repetitive DNA
what does DNA gyrase do
-introduces negative supercoils (destab. base pairing)
- a topoisomerase II
what occurs in topoisomerase I
- removes supercoils
- in pro- and eukaryotes
Where is there some reverse gyrase
in some hyperthermophilic prokarotes
what is a gene
-A gene is a contiguous segment of DNA- i.e. a sequence of nucleotides
-A gene normally encodes a functional product (usually a protein) and is controlled by linked regulatory sequences.
-Flow of genetic information follows a very structured path.
what do CODONS produce
Three nucleotide bases in a DNA sequence (CODON) ultimately specify an amino acid.
what is the central dogma
-the direction of the flow of genetic information is from DNA to RNA to polypeptide
-suggests DNA contains the information needed to make all ofour proteins and RNA is a messenger that carries this information to the ribosomes
-DNA polymerase= replication (DNA to DNA)
-RNA polymerase transcription (DNA to RNA)
-Ribosome= translation (RNA to protein)
what is transcription
-Transcription produces messenger RNA (mRNA)
-mRNA sequence is transcribed (copied) from the DNA strand.
-Codons in the DNA strand now become codons in the mRNA strand.
-Transcription requires the activity of the enzyme RNA polymerase
RNA polymerase helped by sigma factors
what is uracil
one of the 4 nucleotide bases in RNA and is used in cells to carry genetic information and synthesise proteins. Uracil pairs with adenine and RNA releases uracil as instability doesnt matter as much for RNA
What are the main stages in bacterial transcription
- initiation= rna polymerase binds to sequence of DNA called the promotor
- Elongation= template strand is is a template for RNA polymerase. Sigma is released
- Termination= terminators signal the RNA transcript is complete and termination site is reached and chain growth stops
what is the sigma factor
promotor recognition
what is a promotor
site where RNA polymerase binds only 1 strand of DNA is transcribed
5’ to 3’
phosphate group is attached to the 5’ carbon of the sugar ring and hydroxyl group is attached to the 3’ carbon of the sugar ring
what directs protein synthesis
ribosomes
what is the genotype
genetic makeup of the organisms and is a complete set of genes- genotypes can be homozygour dominatn, recessive or heterozygous
what is the phenotype
individuals observe traits- height, eye colour etc
what shape is tRNA
Cloverleaf shape
How many proteins does 2 rRNA molecules have
34 proteins= 50 S
How many proteins does 1 rRNA molecules have
21 proteins= 30S = 50 and 30 gives 70s altogether
what active sites does ribosomes have
3= A, P and E
What is translation
involves decoding a messenger RNA (mRNA) and using its information to build a polypeptide or chain of amino acids
what are the stages of translation
- Initation= components come together with mRNA and tRNA carrying the first amino acid binds to the start codon
- elongation= amino acids are bought to the mRNA by tRNAs and are added one by one to polypeptide chain
- termination= stop codon in the mRNA is recognised by protein release factor and releases the completed polypeptide
What is the genetic code
set of rules by which information encoded in genetic material is trnaslated into proteins (amino acids sequences) by living cells
what are the main amino acids
histidine- His, isoleucine- ile, leucine- leu, lysine- lys, methionine- met, phenylalanine- phe, threonine- thr, tryptophan- trp, and valine- val.
what are the nonessential amino acids
alanine- ala, asparagine- asn, aspartic acid- asp, glutamic acid- glu, and serine- ser
what amino acids only have one codon
met and trp
what are termination signals
stop codons= UAA (orhrc), UAG (amber) and UGA (opal)
what is mRNA
messenger RNA
Contains 3-base units (codons) that specify amino acids
codon= Complimentary to triplet code of DNA
What is rRNA
ribosomal RNA
Comprises the scaffolding for the 70 S ribosome
What is tRNA
transfer RNA
Transfers amino acids to ribosomes for protein synthesis
Specificity for amino acids is due to the anticodon
3 base sequence that is complimentary to codon on mRNA
anticodon= Complimentary to codon
when are genes expressed (some all the time)
Some of these genes will be need to be expressed all the time= These are the genes that are involved in vital biochemical processes= Energy generation and DNA synthesis etc.
Other genes are not expressed all the time, indeed it would be wasteful to keep them on if they had no role to play= They are genes that are switched on an off as required=
Often respond to environmental signals
What is constitutive
a gene that is transcribed at a relatively constant level regardless of cell environmental condictions
what is inducible
the operons whose expression increases quantitatively in response to an enhancer, an inducer or a positive regulator
when were operons discovered
in the 1960s by Jacob, Monod and Lwoff
What are operons
-is a group of genes encoding related functions that are regulated together.
-Transcriptional unit
-They usually control important biochemical processes allowing bacteria to adapt to their environment:
-Metabolism of sugars in E. coli.
-They are only found in prokaryotes
what happens in the metabolic adaption in E.coli
-E. coli can ferment either glucose, which is a monosaccharide, or lactose, which is a disaccharide
-However, lactose needs to be hydrolysed (digested) first
-Specialised enzymes are needed
E. coli prefers to use glucose when it can
-Specialised enzymes are only made if lactose is present and glucose not available.
-The bacteria sense their environment!
how many genes does lac operon contain
3
what is lac Y: lactose permease
allows transport of sugar into cell
what is lac Z: ß-galactosidase
hydrolyse lactose into glucose and galactose
what is lac A: ß-galactosidase transacetylase
involved in lactose breakdown
what does lac I protein encodes
protein called the lac repressor
what is lac repressor protein
regulates expression of lac Z, Y & A
what happens in the absense of lactose
repressor binds to a DNA sequence called operator and blocks the path of RNA polymerase
No transcription occurs
what happens in the presense of lactose
repressor binds to the sugar allolactose and cannot subsequently bind to the operator
RNA polymerase in unhindered and transcription occurs
what are the 4 situations possible in lac operon control
- When glucose is present and lactose is absent the E. coli does not produce β-galactosidase.
- When glucose is present and lactose is present the E. coli does not produce β-galactosidase.
- When glucose is absent and lactose is absent the E. coli does not produce β-galactosidase.
- When glucose is absent and lactose is present the E. coli does produce β-galactosidase
What happens when transcription can occur
Activator protein is bound to DNA
Repressor protein is lifted off the operator site
RNA polymerase sits on the promoter site
Transcription occurs
