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2.1-2.6
The Central Dogma
Gene Expression
DNA → mRNA → Protein
Transcription
DNA copied to make mRNA
Translation
mRNA read to make a protein
translate a sequence of amino acids
protein coding regions of DNA
copied into an mRNA molecule that is used as instructions to make proteins
non-coding DNA
some produces functional RNA
some are regulatory sequences
functional RNA
not used to make protein, but has a biological role
regulatory sequences
help determine when, how a gene will be copied
DNA functions
stores RNA and protein-encoding information; transfers information to daughter cells
stable
RNA functions
carries protein-encoding information; helps to make proteins; catalyzes some reactions
unstable
DNA structure
double-stranded
RNA structure
single-stranded
DNA nucleotide bases
Adenine, Thymine, Guanine, and Cytosine
RNA nucleotide bases
Adenine, Uracil, Guanine, and Cytosine
DNA sugars
deoxyribose and hydrogen
RNA sugars
ribose and OH
RNA polymerase steps
Initiation
Elongation
Termination
Initiation
RNA polymerase binds to control region of DNA
Promoter
helps to initiate the process of transcription with signals
Signals
encoded in the DNA to tell RNA Polymerase where to start and stop
activators
need to be bonded to control regions of the DNA
chromatin
DNA + Histones
Histones
protein complexes responsible for packing DNA
keep DNA organized
hold information to determine ‘open’ or ‘closed’ state of DNA
open
copied or used region of DNA-Euchromatin
closed
not copied or used-Heterochromatin
Euchromatin
loosely coiled
Heterochromatin
tightly coiled
Transcription factor
protein that binds to DNA and regulates gene expression
activate expression
need to bind
Repressors
silence expression and needs to be removed
General Transcription Factors (GTFs)
need to bind to DNA to guide RNA polymerase to bind
RNA plymerase
only reads DNA 3’ → 5’ direction
builds mRNA 5’ → 3’ direction
doesn’t proofread or correct mistakes
Elongation
adding nucleotides to a new DNA strand
template strand
strand that’s being copied in transcription
Termination
RNA polymerase reaches terminator sequence for some genes the mRNA transcript falls away from the DNA template and RNA polymerase
helper protein pulls it away
mRNA during termination
completely detached itself from DNA
either fall off or be pulled away from the DNA
mRNA sequence is translation
it’s translated into an amino acid sequence in the cytoplasm or Rough ER
the genetic code
all organism utilize it the same for representing the 20 amino acids
allows ribosomes from any organisms to produce specific proteins from any mRNA molecule
properties of the genetic code
triplet, non-overlapping, degenerate, unambiguous, punctuated, and universal
triplet
3 bases code for 1 amino acid
(in the RNA form)
non-overlapping
the sets of 3 are read sequentially
punctuated
tells the ribosome where to start and stops
start codon
AUG
stop codons
3
UAA, UAG, UGA
degenerate
the genetic code is redundant; most amino acids have more than 1 codon
unambiguous
codons are exclusive; each specifies only 1 amino acid
universal
the same codons specify the same amino acids ands stop codons in ALL organisms
rRNA
ribosomal RNA
makes up ribosomes, builds proteins
tRNA
transfer RNA
translates the genetic code into the appropriate amino acid
anticodon region
matches to codon on mRNA molecule using complementary base pairing
methionine
first amino acid ALWAYS
small ribosome subunit
binds with AUG codon using complementary base pairing
initiation factors
responsible for assembly of the initiation complex
large subunit joins the complex
the loaded tRNA is now the P site of the large subunit
E
exist site (unloaded tRNA leaves from this location)
P
polymerization site (amino acids are joined together her to form a polymer)
A
access site (new loaded tRNA enters the ribosome in this location)
large subunit catalyzes two reactions
breaks bonds between tRNA in P site and its amino acid
peptide bond forms between that amino acid and the amino acid on tRNA in the A site
if rRNA is destroyed
the activity stops
first tRNA releases its methionine
moves into the E site and dissociated from the ribosome
then tRNA can become loaded again with another amino acid in the cytoplasm
during elognation
steps are repeated as polypeptide elongates
translation ends when
a stope codon enters the A site
ribosome falls of the mRNA
the completed polypeptide is released
have many ribosomes working
on 1 mRNA transcript to amplify synthesis
after termination
protein is then folded
protein synthesis
each ‘valve’ is an important step in getting the right protein
mutation
change in the DNA structure or base sequence of a gene
can occur in RNA replication
intrinsic mutations
factors inside the cell
extrinsic
factors from the external environment
DNA mutations
defective protein or an inability to make certain proteins, can cause diseases
point mutations
change in 1 base pair of DNA
types of point mutations
silent, missense (conservative, non-conservative), nonsense, frameshift (insertion, deletion)
silent mutation
change in the DNA base pair (no affect), but the amino acid stays the same
conservative missense mutation
amino acid does change, but the new amino acid has the same chemical properties
usually small changes to protein structure and function
non-conservative missense mutation
amino acid does change, but the new amino acid has different chemical properties
will change the way a protein folds and how it interacts with other molecules (drastic folding changes)
Nonsense mutation
amino acid does change to a stop codon
ranges from no effect to drastic…depends on location of mutation
Frameshift mutation
addition or deletion of a single DNA base
changes how the mRNA is read (new reading frame for sets of 3 bases/codons
more significant effects on final protein because every amino acid downstream of the mutation is affected
various affects with changes in amino acids
no effect, reduced functionality, loss of function, and gain of function (rare)
loss or gain of fuction
one of the two ways organelles evolve
cystic fibrosis
genetic disease caused by a channel protein mutation
differential gene expression
expression of different by cells with the same genome
Transcription Factors (TF)
are a component that determines which genes are expressed
-bind to control region of gene
reongnize sequence of base pairs on DNA strand
Activators
help general transcription factors and RNA polymerase assemble
Repressor
blocks general transcription factors and RNA polymerase
expressed genes
only occurs if both activators are present and the repressor is absent
little/no transcription
only one activator present
no transcription
activators present and repressor is present
Lactose Intolerance
lactase gene prevents bind of TFs → lactase gene not expressed → can’t digest lactose
Lactase Persistance
a mutation in the control region of the lactase gene the prevents methylation → lactase continues to be expressed → can digest lactose
Non-polar Hormone path to nucleus
cell membrane→ nuclear membrane→ finds protein binding partner→ hormone protein initiate gene expression of target genes
Polar Hormone path to nucleus
bind to signa receptor on cell membrane→ initiates signal pathway in cytoplasm with secondary messengers→ signal cascade at then end…allows it to enter nucleus and bind to DNA to regulate gene expression
signal cascade
a transcription factor changes conformation (shape)
increased translation of genes
can be increased in response to growth cues and other signaling molecules
c-Myc transcriptional activator had a mutation it is always active
the genes would always be expressed even in the absence of growth factors causing inappropriate gene expression
MNK1, a translational activator had a mutation and could NOT be activated
the mRNA that it targets would no longer have increased translation into a protein
mutation on inactive translation
it wouldn’t change but would make less protein
cell theory
The cell is the most basic unit capable of exhibiting the characteristics of life
All living organisms are composed of one or more cells
All cells arise from pre-existing cells (through the process of Mitosis and cytokinesis)
zygote
a fertilized egg
life begins as
a single cell
-undergoes many rounds of cell division to make trillions of cells
reasons for cell division
development, cell replacement, and repair
Development
from a single cell into a multicellular adult
