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