chp.13 bacterial genome replication and expression Flashcards
Explain the central dogma of molecular biology
DNA is the template for its own replication – known as DNA replication, RNA (mRNA, tRNA, rRNA) known as transcription, mRNA is the template for proteins known as translation
DNA replication is done by DNA polymerase
Transcription is done by RNA polymerase
What is the “transformation test”? Who was it conducted by?
the change of nonvirulent organisms into virulent ones via “transformation”
1944- griffith
What did the Hershey-Chase experiment find?
1952- used bacteriophage T2 infection as model, DNA was labeled with 32P, the protein coat was labeled with 35S•only the labeled DNA entered the bacterial cell, labeled protein remained outside of the cell
Mention similarities and differences between DNA and RNA:
1.The nitrogenous bases they contain RNA: adenine, guanine, cytosine, and uracil DNA: adenine, guanine, cytosine, and thymine 2.The sugars they contain RNA: ribose DNA: deoxyribose 3.Whether they are single or double stranded RNA: single stranded DNA: double stranded
What are the three components of nucleotides?
carbon sugar, nitrogen base (purine or pyrimidine), phosphate
Beginning of the nucleic acid strand is known as the 5’ end and the end is known as the 3’ end
There are 2 hydrogen bonds between A and T and 3 hydrogen bonds between G and C
How does a nucleoside differ?
Nitrogen base – pentose sugar
Proteins are polymers known as polypeptides made up of monomers of amino acids
Contain covalent peptide bonds
Structure of primary proteins:
peptide bonds only
Structure of secondary proteins
alpha helices and beta sheets by hydrogen bonds
Structure of tertiary proteins:
give the structure and function, noncovalent bonds + disulfide
Structure of quaternary proteins:
not all proteins have it, can have same type of bonds as tertiary
Explain the process of DNA replication. Consider key players involved in the process, and unique characteristics.
DNA is its own template for replication, Mediated by DNA polymerase, DNA replication is semi-conservative, Replicates the whole genome, process is dependent on a lot of different proteins, It only happens once during cell replication
Complementary DNA/ sense strand
have the same nucleotide sequence as mRNA
Promoter
is located at the start of the gene, responsible for the recognition/binding site for RNA polymerase
Leader sequence
transcribed into mRNA but is not translated into amino acids, contain the Shine-Dalgarno sequence important for initiation of translation
Stop codon:
coding region ends with a stop codon followed by a terminator sequence used to stop transcription
DNA sequence that codes for tRNA and rRNA
Genes coding for tRNA may code for more than a single tRNA molecule or type of tRNA
What are ribozymes?
Spacers between the coding regions of both are removed after transcription, some by the use of special ribonucleases
Explain the process of transcription. Also mention the difference between polycistronic and monocystronic mRNA
RNA synthesis under the direction of DNA, RNA produced has complementary sequence to the template DNA, Three types of RNA are produced: a)mRNA carries the message for protein synthesis b)tRNA carries amino acids during protein synthesis c)rRNA molecules are components of ribosomes
What are the 3 rules of the genetic code?
Rule 1: codons are read 5’ to 3’, Rule 2: codons are non-overlapping, message has no gap, Rule 3: message is translated in a fixed reading frame
What is a codon?
A codon is part of the genetic code “word”, 3 base pairs long, specifies an amino acid
What is an anticodon?
on tRNA is complementary
What is a sense codon?
61 codons that specify the 20 amino acids
What is a start codon?
start site for translation, always AUG, encodes for methionine
What is a stop codon (nonsense codon)?
three codons used as translation termination signals: UGA, UAG, and UAA, do not encode for an amino acid
What are codon exceptions?
Some protists use a single stop codon; the other two code for amino acids instead, Some microbes incorporate two rare amino acids into polypeptides, selenocysteine (Sec, U), pyrrolysine (Pyl, O)
What is code degeneracy?
What causes it?
Since there are more codons (61) than amino acids (20), multiple codons can specify the same amino acid
Wobble position
Explain the process of translation.
Synthesis of polypeptide is directed by the sequence of nucleotides in the mRNA, direction of synthesis: N to C-terminal, The ribosome is the site of translation, coupled transcription/translation in Bacteria/Archaea, polyribosome is a complex of mRNA with several ribosome
What is non-coding RNA?
a functional RNA molecule that is transcribed from DNA but not translated into proteins.
Explain the process of protein maturation
Splicing is the removal of a part (or parts) of a polypeptide before folding, inteinsare the removed portion, exteinsare the portions that remain in protein, Protein function depends on the 3D shape, shape occurs as post translational event, requires folding, association with other proteins (chaperones), delivered to proper subcellular or extracellular
What are molecular chaperones?
What are its functions?
Molecular chaperones are proteins that help other proteins fold, Including: trigger factor, DnaK, DnaJ, GroEL and GroES
protects the cell from thermal damage (heat-shock proteins (HSPs)), aid in transport of proteins across membranes (SecA)
What is protein translocation? Secretion?
Translocation is the movement of proteins from the cytoplasm to plasma membrane or periplasmic space by enzymes known as translocases, Sec system is a general secretion pathway, Tat system secretes only folded proteins, Secretion is the movement of proteins from the cytoplasm to external environment
Explain the process of protein secretion in gram negative bacteria:
Requires crossing two membranes, Some proteins cross in a two-step process: a) translocation to the periplasm by the Sec or Tat system b) secretion across the outer membrane, One-step processes involve structures composed of multiple polypeptides that completely span the periplasm
Macromolecule transport moves proteins that
not been folded yet
Secretory systems:
both exports and inserts integral proteins into the cell membrane
Name the different systems and their specific functions:
SecY, E, G: transmembrane transporter, SecA: recognizes the signal, ATP hydrolyzing enzyme, SecB: prevents folding of the protein, SecD & F: use the proton motive force for translocation
Transported proteins are synthesized as pre-secretory proteins called preproteins
They have a signal peptide at the N-terminus which is recognized by SecA
What is the Tat system?
Translocate folded proteins with “twin” arginine residues (tat) in their signal sequence, Found in Bacteria and some archaea, both Gram-negative and Gram-positive, Moves folded proteins across the plasma membrane
