Central Dogma (Lec) Flashcards
The Central Dogma of Molecular Biology
DNA Replication - Transcription (/Reverse Transcription) - RNA Replication - Translation - Protein
the process of making copies of genetic
information, converting information in DNA into
RNA, and then RNA into proteins
The Central Dogma
of Molecular
Biology
making copies of genetic information
Replication
conversion of DNA to RNA.
Transcription
conversion of RNA to DNA;
viruses only
Reverse Transcription
conversion of mRNA into a protein;
protein synthesis
Translation
Nucleotide sequences that carry
specific instructions for the cell,
usually for protein synthesis
GENES
Smallest hereditary unit; smallest
form of genetic information passed
from parent to offspring
GENES
T/F - A single strand of DNA can carry multiple genes.
T
Genes: Prokaryotes vs Eukaryotes
- In prokaryotes, the
entire gene codes for a
protein/molecule. - In eukaryotes, the gene
consists of coding
(exons) and non-coding
(introns) regions.
Introns are removed and exons are joined together at the end of transcription to form the final mRNA product via a process called?
RNA splicing
Only what percentage of human DNA actually codes for proteins, while non-coding regions still play a role
3%
highly repetitive, non-coding DNA sequences in which longer
ones provide structural stability to chromosomes
Satellites
shorter repeats, and are used to
monitor mutations implicated in diseases, such as cancer
Mini-satellites and microsatellites
DNA Replication occurs in what manner?
semi-conservative manner where DNA strands of the parent DNA becomes the template for the daughter strands.
What is the benefit of the said manner?
It is fast, accurate, and allows for easy repair of DNA. It is also responsible for phenotypic diversity in a few prokaryotic species.
T/F - Replication occurs on both strands of the DNA.
T
strand running from 3’ to 5’ towards the fork is called?
leading strand
strand running from 5’ to 3’ towards the fork is called?
lagging strand
DNA Replication begins at?
origin of replication (a chromosome can have multiple origins)
where replication actively occurs
replication fork
The assembly of proteins that facilitate DNA replication is called the?
replisome
The opening in the DNA where replication takes place is generally called the?
replication bubble
THE REPLISOMES (7):
- DNA Gyrase/Topoisomerase
- Helicase
- Primase
- Clamp Protein
- DNA Polymerase
- DNA Ligase
- Single-stranded Binding Proteins (SSB)
prevents DNA from supercoiling by introducing breaks to the
DNA to relieve stress
DNA Gyrase/Topoisomerase
‘unzips’ the double stranded DNA; breaks the hydrogen bonds between base pairs
Helicase
synthesizes primers which are short RNA sequences that bind to the parent DNA strand, serves as the jumping off paint for DNA polymerase
Primase
keeps DNA polymerase in place
Clamp Protein
synthesizes the new DNA strand
DNA Polymerase
T/F - DNA polymerase can only add nucleotides to an existing nucleotide chain and cannot initiate replication, hence the need for primers
T
joins the Okazaki fragments in the lagging strand
DNA Ligase
stabilizes/protects the single stranded region of
the DNA during replication
Single-stranded Binding Proteins (SSB)
short sections of DNA formed at the time of discontinuous synthesis of the lagging strand during replication of DNA
Okazaki fragments
DNA polymerase synthesizes the new strand by how?
adding nucleotides at the free 3’-hydroxyl group so that the new strand grows from 5’ to 3’.
In the leading strand replication is what?
continuous
In the lagging strand, which runs from 5’ to 3’, replication
In the lagging strand, which runs from 5’ to 3’, replication is?
discontinuous
T/F - Instead of one long strand of new DNA, the polymerase makes use of several primers to make fragments of the new DNA, called Okazaki fragments.
T
joined together at the end of
replication.
Okazaki fragments
Summary of Replication
- Opening of DNA Superstructure. Acetylation of histone lysine
residues weaken binding to DNA, making DNA available for
interaction with enzymes. - DNA Relaxation. DNA tends to supercoil as replication proceeds (think of splitting yarn, where the more it is split, the tighter the unsplit portion becomes); DNA gyrase prevents this.
- DNA Unwinding. Via helicase.
- Primer Synthesis. Via primase.
- DNA Elongation. Via DNA polymerase.
- DNA Ligation. Primers are removed, Okazaki fragments and any breaks in the DNA are joined together via DNA ligase.
involves the replacement of an incorrect of
damaged base with the correct nucleotide.
Base Excision Repair (BER)
Base Excision Repair (BER) requires the ______ of the faulty base from the sugar-phosphate backbone to form an AP site (apurininc/apyrimidinic), followed by the removal of the sugar-phosphate unit of the incorrect nucleotide.
hydrolysis
T/F - DNA polymerase then introduces the correct, and DNA ligase mends the break to complete the repair.
T
T/F - Only one base is removed, but depending on the DNA polymerase used, it may result to a ‘short patch’ (only one nucleotide is replaced) or a ‘long patch’ (more than one nucleotide is replaced)
T
involves the replacement of a stretch of
bases with the correct nucleotides.
Nucleotide Excision Repair (NER)
DIFFERENCE OF BER TO NER
NER removes a section of the DNA strand instead of a single base and makes use of a different DNA polymerase from BER.
the first step in gene expression and occurs in the nucleus (eukaryotes)
Transcription
Before transcription, DNA must first be unwound by?
binding proteins
attaches to the unwound DNA to break the H-bonds between
base pairs
Helicase
the opening in the double helix where transcription takes place
transcription bubble
DNA strand that is transcribed; also called (-) strand or antisense strand
Template strand
DNA strand that is NOT transcribed; also called (+) strand or sense strand
Coding strand
enzyme responsible for RNA synthesis; there are three (3)
types depending on the RNA to be produced
RNA polymerase (RNA pol)
for mRNA
RNA Pol II
Genes have coding (exons) and non-coding (introns) regions, and these make up the?
structural gene
Genes also have the _____ which make up the regulatory regions of the gene.
promoter and terminator regions
where the RNA polymerase initially binds, and is found several nucleotides upstream (means before the beginning of the transcription site; ‘downstream’ means after the beginning of the transcription site)
promoter region
RNA pols cannot recognize the promoter region on their own, and require the help of
transcription factors
T/F - The promoter also identifies which strand is the template.
T
T/F - The coding strand has no promoter region
T
Within the promoter region is the?
consensus sequence and the initiation signal
identifies the precise nucleotide at which
transcription should begin, e.g. the TATA box
consensus sequence
give RNA pol the signal when to start
initiation signal
a string of nucleotides at the end of a gene that
signals RNA pol to transcription.
terminator region
the process of adding the appropriate complementary
nucleotide as RNA pol moves downstream along the gene
Elongation
T/F - RNA pol reads the DNA template from 3’ to 5’, and therefore synthesizes RNA from 5’ to 3’
T
general term used to refer to the product of
transcription.
Transcript
For mRNA, the initial transcript still contains all the introns and
unstranscribed regions, and is referred to as the
pre-mRNA
Pre-mRNA undergoes additional reactions before it can be considered a fully functional mRNA, called the
mature mRNA
three processes of Pre-mRNA
5’ capping – addition of a methylated guanine group to the 5’ end of the transcript.
- 3’ polyadenylation – addition of several adenosine residues to the 3’ end of the transcript, forming a poly(A) tail.
- RNA splicing – removal of the introns from the transcript and joining of the exons.
protects the mRNA from exonucleases; aids in mRNA transport
to the cytosol; allows for the initiation of translation
5’ capping
protects the mRNA from exonucleases
3’ polyadenylation
leaves behind the exons that contains the code for the amino
acids in a protein
RNA splicing
Summary of Transcription
- DNA Unwinding. Binding proteins and helicase unwind and opens up DNA.
- Initiation. RNA pol and transcription factors recognize the promoter sequence and bind to DNA.
- Elongation. RNA pol reads the template and synthesizes the pre-mRNA.
- Termination. RNA pol recognizes the terminator region, stops transcription and releases itself from the template.
- 5’ Capping.
- 3’ Polyadenylation.
- RNA Splicing.
Synthesis of proteins from
mature (spliced) mRNA
Translation
RNA-protein complexes called ____ are used
ribosomes
Has four rRNA (ribosomal RNA) molecules
distributed in two subunits with each subunit: 65% rRNA and 35% protein
Translation
The active site is in the
ribosomal subunit
the active site
rRNA
The predominance of rRNA at the active site
gives it the impression of a?
ribozyme
T/F - The mRNA binds to the small subunit of the
ribosome
T
Three sites in the ribosome:
➢A site – “attachment site”
for tRNAs
➢P site – polypeptide
formation site
➢E site – “exit site” for
tRNAs
T/F - The base sequence in mRNA determines the amino acid sequence in protein synthesis
T
T/F - The base sequence of an mRNA molecule involves 4 different bases - A, C, G, and U
T
A three-nucleotide sequence in an mRNA molecule that codes for a specific amino acid
Codon
In total, how many codons are there?
64
The assignment of the 64 mRNA codons to specific
amino acids
Genetic code
T/F - 3 of the 64 codons are termination codons (STOP codons)
T
The start codon (AUG) also codes for?
Methionine
Stop codons (3)
UAG
UGA
UAA
The genetic code is
____ degenerate
highly (means there are
multiple codons for
most amino acids)
T/F - The degeneracy of the genetic code
makes it less prone to mutations.
T
multiple codons per
amino acid
Degeneracy
T/F - The genetic code is universal
T (Codons for humans are the same for
other organisms as well (with some
exceptions)
Codons are matched with ___ in
corresponding transfer RNAs (tRNAs)
anticodons
Complementary
pairs of codons
Anticodons
T/F - Each codon has a corresponding anticodon, therefore a
corresponding tRNA as well.
T
