Download regulation of cell cycle

http://www.youtube.com/watch?v=Q6ucKWIIFmg&feature=related
ΚΥΤΤΑΡΙΚΟΣ ΚΥΚΛΟΣ
CELL CYCLE
G1: Gap1
Growth and preparation of the chromosomes for replication
S: DNA synthesis (DNA replication)
Synthesis of DNA and duplication of the centrosome
G2: Gap2
Preparation for mitosis
M: Mitosis (nuclear/chromosome separate
and cytoplasm division/cytokinesis)
REGULATION OF CELL CYCLE
Cyclins: major control switches of cell cycle
Cdk: cyclin dependent kinase
adds phosphate to a protein
MPF: maturation promoting factor
Triggers progression through the cell cycle
P53: blocks cell cycle if DNA is damaged
may lead to apoptosis (cell death)
P27: blocks entry into S phase
by binding to cyclin and cdk
The anaphase-promoting complex (APC) (also called the cyclosome)
The APC/C: triggers the events that allow the sister chromatids to separate;
degrades the mitotic cyclin B.
REGULATION OF CELL CYCLE
Cyclins
G1 cyclin (cyclin D)
S-phase cyclins (cyclins E and A)
mitotic cyclins (cyclins B and A)
Their levels in the cell rise and fall with the stages of
the cell cycle.
Cyclin-dependent kinases (Cdks)
G1 Cdk (Cdk4)
S-phase Cdk ((Cdk2)
M-phase Cdk (Cdk1)
Their levels in the cell remain fairly stable, but each
must bind the appropriate cyclin (whose levels
fluctuate) in order to be activated.
They add phosphate groups to a variety of protein
substrates that control processes in the cell cycle.
STEPS IN THE CYCLE
Rising level of G1-cyclins bind to their Cdks and signal the cell
to prepare the chromosomes for replication.
Rising level of S-phase promoting factor (SPF) — which
includes cyclin A bound to Cdk2 — enters the nucleus and
prepares the cell to duplicate its DNA (and its centrosomes).
As DNA replication continues, cyclin E is destroyed, and the
level of mitotic cyclins begins to rise (in G2).
M-phase promoting factor (the complex of mitotic cyclins
with the M-phase Cdk) initiates
assembly of the mitotic spindle
breakdown of the nuclear envelope
condensation of the chromosomes
These events take the cell to metaphase of mitosis.
At this point, the M-phase promoting factor activates the anaphase-promoting
complex (APC/C) which
allows the sister chromatids at the metaphase plate to separate and move to the
poles (= anaphase), completing mitosis;
destroys cyclin B. It does this by attaching it to the protein ubiquitin which targets
it for destruction by proteasomes.
turns on synthesis of G1 cyclin for the next turn of the cycle;
degrades geminin, a protein that has kept the freshly-synthesized DNA in S phase
from being re-replicated before mitosis.
Αποσταθεροποίηση του γονιδιώματος από κακή λειτουργία των σημείων ελέγχου
Λάθη κατά την
αντιγραφή του DNA
Απώλεια τελομερών
Θαύση του DNA
Ενεργοποίηση σημείων ελέγχου
Παύση της κυτταρικής ανάπτυξης
Επιδιόρθωση της βλάβης
Κυτταρικής ανάπτυξης
Κυτταρικός θάνατος
Τα ελεύθερα άκρα του DNA
επάγουν την δημιουργία αναδιατάξεων
ΜΙΤΩΣΗ
INTERPHASE
The cell is engaged in metabolic
activity and performing its
prepare for mitosis (the next four
phases that lead up to and
include nuclear division).
Chromosomes are not clearly
discerned in the nucleus,
although a dark spot called the
nucleolus may be visible.
The cell may contain a pair of
centrioles (or microtubule
organizing centers in plants) both
of which are organizational sites
for microtubules
PROPHASE
Chromatin in the nucleus begins to
condense and becomes visible in the
light microscope as chromosomes.
The nucleolus disappears.
Centrioles begin moving to opposite
ends of the cell and fibers extend
from the centromeres.
Some fibers cross the cell to form the
mitotic spindle.
PROMETAPHASE
The nuclear membrane dissolves,
marking the beginning of
prometaphase.
Proteins attach to the centromeres
creating the kinetochores.
Microtubules attach at the
kinetochores and the
chromosomes begin moving.
METAPHASE
Spindle fibers align the chromosomes along
the middle of the cell nucleus.
This line is referred to as the metaphase
plate.
This organization helps to ensure that in the
next phase, when the chromosomes are
separated, each new nucleus will receive
one copy of each chromosome.
ANAPHASE
The paired chromosomes
separate at the kinetochores
and move to opposite sides of
the cell.
Motion results from a
combination of kinetochore
movement along the spindle
microtubules and through the
physical interaction of polar
microtubules.
TELOPHASE
Chromatids arrive at opposite poles of
cell, and new membranes form around
the daughter nuclei.
The chromosomes disperse and are
no longer visible under the light
microscope.
The spindle fibers disperse, and
cytokinesis or the partitioning of the
cell may also begin during this stage.
CYTOKINESIS
In animal cells, cytokinesis
results when a fiber ring
composed of a protein called
actin around the center of the cell
contracts pinching the cell into
two daughter cells, each with one
nucleus.
In plant cells, the rigid wall
requires that a cell plate be
synthesized between the two
daughter cells.
MITOSIS
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
GO
Many times a cell will leave the cell cycle, temporarily or permanently. It exits
the cycle at G1 and enters a stage designated G0 (G zero). A G0 cell is often
called "quiescent", but that is probably more a reflection of the interests of
the scientists studying the cell cycle than the cell itself. Many G0 cells are
anything but quiescent. They are busy carrying out their functions in the
organism. e.g., secretion, attacking pathogens.
Often G0 cells are terminally differentiated: they will never reenter the cell
cycle but instead will carry out their function in the organism until they die.
For other cells, G0 can be followed by reentry into the cell cycle. Most of the
lymphocytes in human blood are in G0. However, with proper stimulation,
such as encountering the appropriate antigen, they can be stimulated to
reenter the cell cycle (at G1) and proceed on to new rounds of alternating S
phases and mitosis.
G0 represents not simply the absence of signals for mitosis but an active
repression of the genes needed for mitosis. Cancer cells cannot enter G0
and are destined to repeat the cell cycle indefinitely.
ΑΝΙΜΑΤΙΟΝ
http://www.youtube.com/watch?v=lf9rcqifx34&feature=related
http://www.youtube.com/watch?v=2WwIKdyBN_s&feature=related
http://www.youtube.com/watch?v=s1ylUTbXyWU&feature=player_embedded#
ΜΕΙΩΣΗ
MEIOSIS
Meiosis I as in mitosis
Meiosis II is similar to mitosis. However, there is no "S" phase. The
chromatids of each chromosome are no longer identical because of
recombination. Meiosis II separates the chromatids producing two
daughter cells each with 23 chromosomes (haploid), and each
chromosome has only one chromatid.
Animation:
http://www.biology.arizona.edu/CELL_BIO/tutorials/meiosis/page3.html
http://www.youtube.com/watch?v=MqaJqLL49a0&feature=related
http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related
ΑΝΤΙΓΡΑΦΗ
Replication Bubble Forms
Helper proteins
Directionality
Helper proteins
Multiple Sites of Replication Origin of DNA
5’ to 3’ replication occurs in eukaryotes just
like in prokaryotes
In this micrograph, a
replication
bubble is visible along the
DNA of cultured cells.
Arrows indicate DNA
replication direction at the
two ends of each bubble.
E. coli DNA replication
Leading strand
ssDNA binding protein
Helicase
primosome
primase
Lagging strand
replicating
DNA polymerase III
Active sites
RNA primer
Ligase
DNA polymerase I
Step 3: Primase
Step 4. Elongation
Okazaki Fragments
ΑΝΤΙΓΡΑΦΗ DNA
A. Ελικάση: απελίκωση και διαχωρισμός
των αλυσίδων DNA.
SSB: πρωτεϊνικό σύμπλοκο με
μονόκλωνο DNA.
B. RNA πριμάση: δημιουργία υποκινητή
RNA.
DNA πολυμεράση ΙΙΙ: έναρξη σύνθεσης
της οδηγού αλυσίδας.
Γ. DNA πολυμεράση ΙΙΙ: έναρξη σύνθεσης
της συνοδού αλυσίδας.
δημιουργία κομματιών
Okazaki.
Δ. DNA πολυμεράση ΙΙΙ: επιμήκυνση και
ολοκλήρωση σύνθεσης της οδηγού
αλυσίδας.
Ε. Συνθετάση (Λιγάση): σύνδεση των
τροποποιημένων κομματιών Okazaki.
ΣΤ. Ολοκλήρωση της σύνθεση της οδηγού
αλυσίδας και της συνοδού.
Nucleosome Assembly
Unique to eukaryotic replication process
Animation:
207.207.4.198/pub/flash/24/24.html
http://www.youtube.com/watch?v=rpwjZX_z5rg&feature=related
http://www.youtube.com/watch?v=teV62zrm2P0&feature=player_embedded#
http://www.youtube.com/watch?v=-mtLXpgjHL0&feature=related
ΚΕΝΤΡΙΚΟ ΔΟΓΜΑ
ΚΕΝΤΡΙΚΟ ΔΟΓΜΑ
The Central Dogma Of Molecular Biology
Replication
DNA duplicates
Transcription
RNA synthesis
Translation
Protein synthesis
4-Letter Code
A,T.G,C
4-Letter Code
A,U.G,C
20-Letter Code
Amino Acids
ΚΕΝΤΡΙΚΟ ΔΟΓΜΑ ????????
General
Special
Unknown
DNA → DNA
RNA → DNA
protein → DNA
DNA → RNA
RNA → RNA
protein → RNA
RNA → protein DNA → protein protein → protein
ribose
deoxyribose
Classification of RNAs
RNAs
Functional
Informational
ribosomal RNAs
transfer RNAs
messenger RNAs
Forms complexes with proteins
Vital for protein translation
Vital for protein
translation
Intermediates
in decoding genes into proteins
Small nuclear RNAs
Small nucleolar RNAs
Small cytoplasmic RNAs
Small Interfering RNAs
MicroRNA
snRNAs
snoRNA
scRNA
siRNA
miRNA
Molecule of the year 2002
microRNA (miRNA)
Sequences produced within the cell by transcription from individual miRNA genes, introns, or
from polycistronic clusters of closely related miRNA genes. ‘pri-miRNAs’, are several
thousand bases long.
miRNAs only have complementarity in a crucial ‘seed’ region 2-8 bases long in the 5’ region.
This can make it possible for some miRNAs to pair with hundreds of high- and low-affinity
mRNA targets (one-to-many), and conversely, multiple miRNAs may target a single mRNA
(many-to-one).
This mechanism seems to be a very ancient one in evolution, having been detected
throughout plant and animal systems in various forms, and even in viruses.
microRNA (miRNA)
1. Processed within the nucleus by a
‘microprocessor complex’ containing a doublestranded RNA-specific ribonuclease known as
Drosha, and its binding partner Pasha, to give
hairpin RNA precursors, the ‘pre-miRNAs’.
2. Transported to the cytoplasm using Exportin-5.
3. Cleavage by the endonuclease Dicer results in a
double-stranded miRNA and then incorporated into
an RNA-induced silencing complex (RISC).
4. A single mature miRNA strand is selected and
matured and the other is degraded.
5. The active miRNAs down-regulate gene
expression by translational repression and/or
messenger RNA (mRNA) cleavage, mediated by
the RISC, in a manner similar to short interfering
RNA (siRNA).
http://www.youtube.com/watch?v=AfXmDAqgFIg&feature=related
http://www.youtube.com/watch?v=gZZyxVP02UU&feature=related
Messenger Ribonucleic Acid (mRNA)
is a molecule of RNA encoding a chemical "blueprint" for a protein product.
The brief life of an mRNA molecule begins with transcription and ultimately ends in
degradation. During its life, an mRNA molecule may also be processed, edited, and
transported prior to translation. Eukaryotic mRNA molecules often require extensive
processing and transport, while prokaryotic molecules do not.
5' cap
The 5' cap is a modified guanine nucleotide added to the "front" (5' end) of the pre-mRNA using a
5',5-Triphosphate linkage. This modification is critical for recognition and proper attachment of
mRNA to the ribosome, as well as protection from 5' exonucleases. It may also be important for
other essential processes, such as splicing and transport.
Coding regions
Coding regions are composed of codons, which are decoded and translated into one (mostly
eukaryotes) or several (mostly prokaryotes) proteins by the ribosome. Coding regions begin with
the start codon and end with the one of three possible stop codons. In addition to protein-coding,
portions of coding regions may also serve as regulatory sequences in the pre-mRNA as exonic
splicing enhancers or exonic splicing silencers.
3' poly(A) tail
The 3' poly(A) tail is a long sequence of adenine nucleotides (often several hundred) added to the
"tail" or 3' end of the pre-mRNA through the action of an enzyme, polyadenylate polymerase. In
higher eukaryotes, the poly(A) tail is added onto transcripts that contain a specific sequence, the
AAUAAA signal. The importance of the AAUAAA signal is demonstrated by a mutation in the
human alpha 2-globin gene that changes the original sequence AATAAA into AATAAG, which can
lead to hemoglobin deficiencies.
Transfer RNA (abbreviated tRNA)
a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to
a growing polypeptide chain at the ribosomal site of protein synthesis during
translation. It has a 3' terminal site for amino acid attachment. This covalent
linkage is catalyzed by an aminoacyl tRNA synthetase. It also contains a
three base region called the anticodon that can base pair to the
corresponding three base codon region on mRNA. Each type of tRNA
molecule can be attached to only one type of amino acid, but because the
genetic code contains multiple codons that specify the same amino acid,
tRNA molecules bearing different anticodons may also carry the same amino
acid.
The 5'-terminal phosphate group.
The acceptor stem is a 7-bp stem made by the base pairing of the 5'-terminal
nucleotide with the 3'-terminal nucleotide (which contains the CCA 3'-terminal
group used to attach the amino acid).
CCA sequence is important for the recognition of tRNA by enzymes critical in
translation. In prokaryotes, the CCA sequence is transcribed. In eukaryotes,
the CCA sequence is added during processing and therefore does not appear
in the tRNA gene.
The D arm is a 4 bp stem ending in a loop that often contains dihydrouridine.
The anticodon arm is a 5-bp stem whose loop contains the anticodon.
The T arm is a 5 bp stem containing the sequence TΨC where Ψ is a
pseudouridine.
Bases that have been modified, especially by methylation, occur in several
positions outside the anticodon. The first anticodon base is sometimes
modified to inosine (derived from adenine) or pseudouridine (derived from
uracil).
http://www.youtube.com/watch?v=4MRCH_J7Fhk&feature=player_embedded#
http://telstar.ote.cmu.edu/Hughes/HughesArchive/tutorial/polypeptide/tutorial.swf
Ribosomal RNA (rRNA)
a type of RNA synthesized in the nucleolus by RNA polymerase I, is the central
component of the ribosome, the protein manufacturing machinery of all living cells.
The function of the rRNA is to provide a mechanism for decoding mRNA into amino
acids and to interact with the tRNAs during translation by providing peptidyl
transferase activity.
Small subunit ribosomal RNA, 5'
domain taken from the Rfam
database.
The ribosome
is composed of two subunits, named for how
rapidly they sediment when subject to
centrifugation. tRNA is sandwiched between the
small and large subunits and the ribosome
catalyzes the formation of a peptide bond
between the 2 amino acids that are contained
in the tRNA.
The ribosome also has 3 binding sites called A,
P, and E.
The A site in the ribosome binds to an
aminoacyl-tRNA (a tRNA bound to an amino
acid).
The NH2 group of the aminoacyl-tRNA which contains the new amino acid, attacks the
carboxyl group of peptidyl-tRNA (contained within the P site) which contains the last amino
acid of the growing chain called peptidyl transferase reaction.
The tRNA that was holding on the last amino acid is moved to the E site, and what used to be
the aminoacyl-tRNA is now the peptidyl-tRNA.
A single mRNA can be translated simultaneously by multiple ribosomes.
Type
Size
Large subunit
Small subunit
prokaryotic
70S
50S (5S, 23S)
30S ((16S)
eukaryotic
80S
60S (5S, 5.8S, 28S)
40S (18S)
http://telstar.ote.cmu.edu/Hughes/HughesArchive/tutorial/polypeptide/tutorial.swf
Proteins
large organic compounds made of amino acids arranged in a linear chain and joined
together by peptide bonds between the carboxyl and amino groups of adjacent amino acid
residues. The sequence of amino acids in a protein is defined by a gene and encoded in the
genetic code. Although this genetic code specifies 20 "standard" amino acids, the residues in
a protein are often chemically altered in post-translational modification: either before the
protein can function in the cell, or as part of control mechanisms. Proteins can also work
together to achieve a particular function, and they often associate to form stable complexes.
amino acid
a molecule that contains both amine and carboxyl functional groups. In biochemistry,
this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R
is an organic substituent. In the alpha amino acids, the amino and carboxylate groups
are attached to the same carbon, which is called the α–carbon. The various alpha
amino acids differ in which side chain (R group) is attached to their alpha carbon. They
can vary in size from just a hydrogen atom in glycine, through a methyl group in alanine,
to a large heterocyclic group in tryptophan.
Name Abbr. Linear structure formula
======================================
Alanine ala A CH3-CH(NH2)-COOH
Arginine arg R HN=C(NH2)-NH-(CH2)3-CH(NH2)COOH
Asparagine asn N H2N-CO-CH2-CH(NH2)-COOH
Aspartic acid asp D HOOC-CH2-CH(NH2)-COOH
Cysteine cys C HS-CH2-CH(NH2)-COOH
Glutamine gln Q H2N-CO-(CH2)2-CH(NH2)-COOH
Glutamic acid glu E HOOC-(CH2)2-CH(NH2)-COOH
Glycine gly G NH2-CH2-COOH
Histidine his H NH-CH=N-CH=C-CH2-CH(NH2)-COOH
Isoleucine ile I CH3-CH2-CH(CH3)-CH(NH2)-COOH
Leucine leu L (CH3)2-CH-CH2-CH(NH2)-COOH
Lysine lys K H2N-(CH2)4-CH(NH2)-COOH
Methionine met M CH3-S-(CH2)2-CH(NH2)-COOH
Phenylalanine phe F Ph-CH2-CH(NH2)-COOH
Proline pro P NH-(CH2)3-CH-COOH
Serine ser S HO-CH2-CH(NH2)-COOH
Threonine thr T CH3-CH(OH)-CH(NH2)-COOH
Tryptophan trp W Ph-NH-CH=C-CH2-CH(NH2)-COOH
Tyrosine tyr Y HO-p-Ph-CH2-CH(NH2)-COOH
Valine val V (CH3)2-CH-CH(NH2)-COOH
The Central Dogma Of Molecular Biology
ΓΕΝΕΤΙΚΟΣ ΚΩΔΙΚΑΣ
A gene begins with a codon for the amino acid methionine and ends with one of 3 stop codons. The codons
between the start and stop signals code for the various AAs of the gene product but do not include any of the
3 stop codons. When examining an unknown DNA sequence, one indication that it may be part of a gene is
the presence of an open reading frame or ORF.
An ORF is any stretch of DNA that when transcribed into RNA has no stop codon.
A computer program can be used to check an unknown DNA sequence for ORFs.The program
transcribes each DNA strand into its complementary RNA sequence and then translates the RNA
sequence into an amino acid sequence. Each DNA strand can be read in three different reading
frames. This means that the computer must perform six different translations for any given
double-stranded DNA sequence.
ΜΕΤΑΓΡΑΦΗ
The Basic Transcription Unit Model
terminator
Let’s look closely at the process of transcription.
Promoter of RNA polymerase II
Affects rate of transcription
http://www.youtube.com/watch?v=WsofH466lqk
In principle, locating genes should be easy. DNA sequences that code for proteins begin with the
three bases ATG that code for the amino acid methionine and they end with one or more stop
codons; either TAA, TAG or TGA. Unfortunately, finding genes isn't always so easy
Four key components of transcription
•
•
•
•
Promoter
Transcription start site
RNA coding region
The Terminator
Process of Bacterial Transcription
• Initiation
• Elongation
• Termination
Eukaryotic Transcription
•
•
•
•
•
•
3 distinct RNA polymerases in a eukaryotic cell nucleus define the three major classes of eukaryotic
transcription unit:
polymerase
location
type of RNA transcribed
I
Nucleus/nucleolus
II
nucleus
pre-mRNA, some snRNAs, some snoRNAs
III
nucleus
small RNA such as tRNA and 5S Rrna, and snRNAs
Large rRNA
There may be as many as 14 subunits in an eukaryotic RNA polymerase; the total molecular weight is typically 500-700 kD.
Eukaryotic RNA polymerases cannot find or bind to a promoter by themselves. They require the binding of assembly factors and a
positional factor to locate the promoter and to orient the polymerase correctly. As we will see, the positional factor is the same in
all cases.
Class I Transcriptional Units: Class I genes or transcriptional units are transcribed by RNA polymerase I in the nucleolus. The
best-studied examples are the rRNA transcription units. RNA polymerase I is a complex of 13 subunits.
Class II Transcription Units: All genes that are transcribed and expressed via mRNA are transcribed by RNA polymerase II.
RNA polymerase II (12 subunits) can transcribe RNA from nicked dsDNA templates or from ssDNA templates. However, by itself,
it cannot initiate transcription at a promoter. In this respect, it resembles the core form of bacterial RNA polymerase.
Class III Transcription Units: Class III genes are principally those for small RNA molecules in the cell. The best studied examples
are the 5S rRNA gene -- which has been studied extensively in Xenopus laevis, and tRNA genes.
The enzyme:RNA polymerase III is the largest of the three RNA polymerases with 17 subunits and a molecular weight of over 700
kD. It is moderately sensistive to a-amanitin. It is also the most active.
The DNA strand that codes for the protein is called the sense strand because its sequence reads
the same as that of the messenger RNA. The other strand is the antisense strand and serves as
the template for RNA polymerase during transcription.
Initiation
RNAP = RNA polymerase
In transcription, one strand of DNA, the non-coding strand, is used as a template for RNA
synthesis. As transcription proceeds in the 5' → 3' direction, and uses base pairing
complimentarity with the DNA template to specify the correct copying, the DNA template
strand is that oriented in the 3' → 5' direction. The strand that is not used as the template is
called the coding strand, and has the DNA sequence that reflects that of the RNA produced.
Transcription begins with the binding of RNA polymerase to the promoter. In prokaryotes, the
RNA polymerase is a core enzyme consisting of five subunits: 2 α subunits, 1 β subunit, 1 β'
subunit, and 1 ω subunit. At the start of initiation, the core enzyme is associated with a sigma
factor (number 70) that aids in finding the appropriate -35 and -10 basepairs downstream of
promoter sequences. Transcription initiation is far more complex in eukaryotes, the main
difference being that eukaryotic polymerases do not recognize directly their core promoter
sequences. Unlike DNA replication, transcription does not need a primer to start because RNA
polymerase does not require a primer. The DNA unwinds and produces a small open complex
and synthesis begins on only the template strand.
Elongation
Unlike DNA replication, mRNA transcription can involve multiple RNA polymerases on
a single DNA template, so many mRNA molecules can be produced from a single
copy of a gene. This step also involves a proofreading mechanism that can replace an
incorrectly added RNA molecule.
Termination
Bacteria use two different strategies for transcription termination: in Rho-independent
transcription termination, RNA transcription stops when the newly synthesized RNA
molecule forms a hairpin loop, followed by a run of Us, which makes it detach from the
DNA template. In the "Rho-dependent" type of termination, a protein factor called "Rho"
destabilizes the interaction between the template and the mRNA, thus releasing the newly
synthesized mRNA from the elongation complex. Transcription termination in eukaryotes is
less well understood. It involves cleavage of the new transcript, followed by templateindependent addition of As at its new 3' end, in a process called polyadenylation.
5' cap
The 5' cap is a modified guanine nucleotide added to the "front" (5' end) of the premRNA using a 5',5-Triphosphate linkage. This modification is critical for recognition and
proper attachment of mRNA to the ribosome, as well as protection from 5'
exonucleases. It may also be important for other essential processes, such as splicing
and transport.
3' poly(A) tail
The 3' poly(A) tail is a long sequence of adenine nucleotides (often several hundred) added to the
"tail" or 3' end of the pre-mRNA through the action of an enzyme, polyadenylate polymerase. In
higher eukaryotes, the poly(A) tail is added onto transcripts that contain a specific sequence, the
AAUAAA signal. The importance of the AAUAAA signal is demonstrated by a mutation in the
human alpha 2-globin gene that changes the original sequence AATAAA into AATAAG, which can
lead to hemoglobin deficiencies.
RNA splicing
It is easier to locate genes in bacterial DNA than in eukaryotic DNA.
In bacteria, the genes are arranged like beads on a string. Each gene consists of a single ORF.
The situation in eukaryotic organisms is complicated by the split nature of the genes. Most
eukaryotic genes take the form of alternating EXONS and INTRONS. Each exon is an ORF that
codes for amino acids. The intron sequences do not code for amino acids and contain internal stop
codons.
Splicing: 3 components are required
Note some important aspects of the 5’ and 3’ ends
5’ phosphodiester of G
2’ OH of A
http://www.sumanasinc.com/webcontent/anisamples/molecularbiology/mRNAsplicing.html
One of the surprises of the Human Genome Project was the relatively small number of genes
found - about 25,000. One might ask, "How can something as complicated as a human have only
25 percent more genes than the tiny roundworm C. elegans?" Part of the answer seems to involve
alternative splicing. Alternative splicing refers to the process by which a given gene is spliced into
more than one type of mRNA molecule.
http://www.youtube.com/watch?v=OEWOZS_JTgk&feature=related
ΜΕΤΑΦΡΑΣΗ
In addition to the APE sites there is an mRNA binding groove
that holds onto the message being translated
=EF-1
Proper reading of the
anticodon is the second
important quality control
step ensuring accurate
protein synthesis
Elongation factors
Introduce a two-step
“Kinetic proofreading”
A second elongation factor
EF-G or EF-2, drives the
translocation of the ribosome
along the mRNA
Together GTP hydrolysis
by EF-1 and EF-2 help drive
protein synthesis forward
Termination of translation
is triggered by stop codons
Release factor enters
the A site and triggers
hydrolysis the peptidyl-tRNA
bond leading to release of
the protein.
Release of the protein causes
the disassociation of the
ribosome into its constituent
subunits.
http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related
Signaling:
http://www.youtube.com/watch?v=tMMrTRnFdI4&feature=related
Inner life of cell:
http://www.youtube.com/watch?v=CVUnzk40npw