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Creado por Sarah Pirbhai
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Biology Unit 5.1.1-
Cellular Control
- How DNA codes for proteins
- Key Words:
- genes- a
length of DNA
that codes for
one or
polypeptide
chains
- polypeptide-
polymer consisting of
a chain of amino acid
residues joined by a
peptide bond.
- genome- entire DNA sequence of one
organism. Human genomes consist of 3
billion nucleotide base pairs
- Protein- Large
polypeptide (100+
amino acids) some
proteins consist of
more than one
polypeptide chain
- genes- a
length of DNA
that codes for
one or
polypeptide
chains
- A gene is...
- sequence of nucleotide
bases that code for
polypeptides
- human genome = 25 000
genes (some in
mitochondria and linear
chromosomes)
- occupies locus on
chromosome
- codes for polypeptides such as...
- haemoglobin
- immunoglobulins
- antigens
- enzymes
- electron carriers
- structural proteins
- cell surface receptors
- actin and myosin
- tubulin
- channel
- haemoglobin
- sequence of nucleotide
bases that code for
polypeptides
- Genetic code
- triplet code- 3
nucleotide bases
that code for an
amino acid (20
acids) 4x4=16 not
enough, 4x4x4=64
more than enough
- Degenerate code- All amino
acids have more than one
code (Not MET)
- Stop
codons at
end of chain
- wide spread
info, not
universal
- triplet code- 3
nucleotide bases
that code for an
amino acid (20
acids) 4x4=16 not
enough, 4x4x4=64
more than enough
- Protein Synthesis,
1st Step-
Transcription
- Free DNA nucleotides in the
nucleoplasm and free RNA
nucleotides in nucleolus.
Nucleotides are activated
(Have 2 extra phosphoryl
groups)
- 4 Different activated RNA
nucleotied: ATP, GTP, CTP,
UTP
- Steps:
- 1. DNA that makes up
gene dips out of
nucleolus. H+ Bonds
break and DNA molecule
unwinds and unzips.
- 2. RNA nucleotides
bind with Hydrogen
bonds: U-A, G-C, A-T
(on template strand).
catalysed reaction
with RNA polymerase
- 3. Two extra phosphoryl
groups needed. Released
Energy for bonding adjacent
nucleotides
- 4. mRNA produced =
complementary to nucleotide
Base sequence on template
therefore, copy of base
sequences on coding strand of
the length of DNA
- 5. mRNA released
from DNA and
passes out of the
nucleus, through a
pore to the ribosome
- 1. DNA that makes up
gene dips out of
nucleolus. H+ Bonds
break and DNA molecule
unwinds and unzips.
- Free DNA nucleotides in the
nucleoplasm and free RNA
nucleotides in nucleolus.
Nucleotides are activated
(Have 2 extra phosphoryl
groups)
- Key Words:
- Translation-
2nd Step of
Protein
Synthesis
- Translation is...
- assembly of
polypeptides
(proteins) at
ribosomes
- second stage of protein
synthesis (amino acids
assembled into polypeptides)
- assembled according to
codon (triplets of
nucleotide bases.
- occurs in ribosomes
- assembly of
polypeptides
(proteins) at
ribosomes
- Ribosomes...
- assembled in
nucleolus of
eukaryote cells
from ribosomal
RNA and
protein
- move along
mRNA through
groove- reads
code and
assembles
amino acids in
correct order to
form a
functional
protein
- sequence of
amino acids
important
because...
- forms primary structure (determines
tertiary structure), how its held in 3D form
with hydrogen or ionic bonds, hydrophobic
reactions between R groups, tertiary
structure allows protein to function, if
altered cant function properly
- forms primary structure (determines
tertiary structure), how its held in 3D form
with hydrogen or ionic bonds, hydrophobic
reactions between R groups, tertiary
structure allows protein to function, if
altered cant function properly
- assembled in
nucleolus of
eukaryote cells
from ribosomal
RNA and
protein
- Transfer RNA (tRNA)
- made in
nucleus and
pass into
cytoplasm
- length of RNA
that folds into
hairpin (clover)
shape
- 3 exposed bases
where a
particular amino
acid can bind
- on other end: 3 unpaired
nucleotide bases- anticodon.
each binds temporarily with
complimentary codon
- made in
nucleus and
pass into
cytoplasm
- Steps:
- 1. mRNA binds to
ribosomes- Translation
begins. AUG codes for
Methonine. Anticodon of
tRNA forms base pairs with
codon on mRNA
- .2. Another tRNA molecule
(Serine) occupies second spot
in ribosomes. Peptide bond
formed with MET and SER
- 3. Ribosomes move one codon
along mRNA. MET tRNA leaves
and another arrives and
occupies next vacant position.
tRNA ensures genetic message
is read correctly
- 4. Ribosome moves on
and add on more amino
acids to polypeptide
chain. carries on until
stop codon appears (UAA,
UAG, UGA). Translation is
complete
- 1. mRNA binds to
ribosomes- Translation
begins. AUG codes for
Methonine. Anticodon of
tRNA forms base pairs with
codon on mRNA
- Some proteins activated by cAMP
which activates them by changing
3D shape so its easier to fit their
complementary molecule
- Protein Synthesis in
Prokaryoes- Translation begins
as soon as mRNA made
because DNA not held in a
nucleus
- Translation is...
- Mutations
- Key Words...
- Mutations- change in amount
of or arrangement of genetic
material in a cell (randomly
occuring)
- chromosome mutations-
change to part or whole
chromosome. Changes to
the structure such as
deletion, inversion and
translocation.
- DNA mutations- changes to
genes due to changes in
nucleotide base sequences
- Mutations- change in amount
of or arrangement of genetic
material in a cell (randomly
occuring)
- Occurs during replication.
substances may cause
mutations- Tar, UV, X/Gamma
rays
- DNA Mutations
- Occur during nuclear division
- Meiosis- can
be passed to
offspring
- Mitosis- Somatic
mutations- not passed
to offspring,
contributes ot ageing
process/cancer
- Meiosis- can
be passed to
offspring
- 2 Types:
- 1. Point Mutations-
one base pair
replaces another-
Substituted base pair
- Cause:
- Missense: is a point
mutation in which a
single nucleotide is
changed, resulting in a
codon that codes for a
different amino acid
- Nonsense:
mutation causes a
stop in the
polypeptide chain.
therefore, not a
full chain and cant
form any functions
- Silent Mutations-
Mutation within
triplet code that
doesnt affect the
amino acid or
polypeptide chain
- Missense: is a point
mutation in which a
single nucleotide is
changed, resulting in a
codon that codes for a
different amino acid
- Cause:
- 2. Insertion/Deletion mutations- 1+
nucleotide pairs inserted or
deleted from DNA. Causes a
Frameshift
- Causes Frameshift, deletion of one gene
that causes a frameshift because of this,
different amino acids would form with no
stop codon
- Causes Frameshift, deletion of one gene
that causes a frameshift because of this,
different amino acids would form with no
stop codon
- 1. Point Mutations-
one base pair
replaces another-
Substituted base pair
- Occur during nuclear division
- Diseases due
to mutations:
- Deletion of Triplet base pair =
deletion of amino acids from
approx 1480 amino acids in
normal polypeptide chain: Cystic
Fibrosis
- Mutation on Codon 6 for Beta
polypeptide chains of
haemoglobin cause valine to be
inserted rather than glutamic
acid: Sickle Cell anaemia
- repeated CAG sequence if
expand a threshold number
protein is altered sufficiently:
Huntingtons
- Deletion of Triplet base pair =
deletion of amino acids from
approx 1480 amino acids in
normal polypeptide chain: Cystic
Fibrosis
- Neutral effects
- allele- alternate version
of a gene, still at same
locus on chromosome
and cods for some
polypeptides but
alterations to base
alters structure
- may not
change
organisms
if...
- in non
coding
region of
DNA
- silent
mutations
- in non
coding
region of
DNA
- change/mutation
may not have an
advantage or
disadvantage and
so has neutral
effects.
- allele- alternate version
of a gene, still at same
locus on chromosome
and cods for some
polypeptides but
alterations to base
alters structure
- harmful or
beneficial
effects:
- early human melanin
protected harmful
effects of UV light,
but can still synthesis
Vitamin D
- mutations to skin colour
gene (pale skin, would
have more burns and
suffer skin cancers)
- migration to more temperate
climates, sun not intense enough
for Dark.
- Those with paler
skins would be
advantaged as
they can
synthesis
Vitamin D
- Low vitamin D...
- rickets
- narrow pelvis
- Cancer
- Heart disease
- rickets
- Low vitamin D...
- early human melanin
protected harmful
effects of UV light,
but can still synthesis
Vitamin D
- Key Words...
- The Lac Operon
- Enzyme induction
- enzymes involved in
basic cellular functions
are synthesised at a
constant rate
- inducible enzymes
synthesised at variable
rates according to cell
circumstances
- Bacteria adapt to their
environment by producing
enzyme to metabolise certain
nutrients only when present
- E coli repress glucose but
also use lactose as a
respiratory substance
- E coli grown with no lactose can be placed where there
is lactose. at first they cant metabolise lactose because
they have small amounts of the 2 enzymes to metabolise.
the two enzymes are:
- Beta galactosidase- catalyses
the hydrolysis of lactose to
glucose and galactose
- Lactose Permease-
transports lactose into
cells
- Beta galactosidase- catalyses
the hydrolysis of lactose to
glucose and galactose
- when added to lactose
environment, bacteria increases
rate of synthesis of the 2 enzymes
(inducer)
- enzymes involved in
basic cellular functions
are synthesised at a
constant rate
- Lac System Genes form an Operon
- Regulatory Gene- Not part of operon,
a gene involved in controlling the
expression of one or more other
genes.
- Structural Genes
- Z: codes for- Beta Galactosidase
- Y: Codes for- Lactose Permease
- each consists of
sequence of base
pairs that can
transcribe to mRNA
- Z: codes for- Beta Galactosidase
- Opperator region- switches genes on and off
- Promoter region- RNA
polymerase binds to begin
transcription of structural
genes
- Regulatory Gene- Not part of operon,
a gene involved in controlling the
expression of one or more other
genes.
- Absent Lactose
- 1. Regulatory gene expressed, repressor
protein synthesised. 2 binding sites:
lactose and opperator region
- 2. repressor protein binds with
opperator region and covers
promoter where RNA polymerase
normally attaches
- 3. Structural genes not transcribed
- 4. without mRNA, gene cant be
transcribed, both enzymes not
synthesised
- 1. Regulatory gene expressed, repressor
protein synthesised. 2 binding sites:
lactose and opperator region
- With Lactose
- 1. lactose binds to site on
repressor protein, causes
repressor to change shape
and cant bind with operator.
Lactose = inhibitor
- 2. Promotor region
remains unblocked, RNA
polymerase binds and
initiates transcription of
mRNA for Z and Y genes
- 3. operator-repressor-inducer
system acts as switch and
allows transcription and
subsequent translations of Z
and Y into Lac enzyme
- 4. E coli can use lactose permease to bring
lactose into cell and convert lactose to
glucose and galactose with beta
galactosidase. sugars used for respiration
and gaining energy from lactose
- 1. lactose binds to site on
repressor protein, causes
repressor to change shape
and cant bind with operator.
Lactose = inhibitor
- Enzyme induction
- Genes and Body Plans
- Drosophilia development
- 1. one miotic
division every 6-10
mins
- 2. no new cell
membranes and
multi-nucleate syncytium
formed.
- 3. 8th division-
256 nuclei
migrate to
outerparts
- 4. 11th division-
nuclei form outer
layer around
central yolk filled
core.
- 5. 14th Division- slows
down (60 mins). nuclear
genes switch from
replicate to transcribe
- 6. membrane
invaginates around
6000 nuclei.
therefore, cells form
single outer layer
- 7. 2-3 hours- embryo develops into
segements corresponding to organisation
of organisms body plans. Md, Mx, Lb=
Head; T1-T3= Thoracic; A1-A8=
abdominal
- 8. Metamorphisis- legs,
wings, antennae.
- Genetic control
- Homeobox genes: controls
development of body plans of
an organism (Polarity, position
of organs)
- maternal effect
genes- polarity
- segmentation
genes- polarity
of segments
- Homeobox genes: controls
development of body plans of
an organism (Polarity, position
of organs)
- 1. one miotic
division every 6-10
mins
- Genetic control of
development in other
organisms
- Homeobox genes contain 180 base
pairs therefore, polypeptides of 60
amino acids
- Hox clusters-
arrangements of
homebox genes
- Nematodes (roundworms)- 1 Hox Clusters
- Drosophilia- 2
- Vertebrates- 4, 9-11
genes, separate
chromosomes
- Nematodes (roundworms)- 1 Hox Clusters
- Homeobox genes contain 180 base
pairs therefore, polypeptides of 60
amino acids
- Retinoic Acid and birth defects- too much
retinoic acid (Vitamin A) interferes with
expression of genes therefore, birth defects
may iccur. Vitamin A activates homeobox
genes
- Drosophilia development
- Apoptosis
- Programmed cell death
- hayflick constant- 50 miotic divisions
that undergo a series of biochemical
events before tidy cell death
- necrosis- messy cell death
- How is it controlled? Cell signaling
- Cytokines (made
by cells immune
system)
- hormones
- nitric oxide- induces
apoptosis by making
inner mitochondrial
membrane permeable
to H+ and dissipitates
proton gradient
- Cytokines (made
by cells immune
system)
- Development
- Children (8-14):
20-30 billion cells a
day
- Adults:
50-70 billion
cells a day
- too little apoptosis:
tumours, cancers
- Too Much: cell loss,
degeneration
- Children (8-14):
20-30 billion cells a
day
- Steps
- 1. enzymes breakdown cell
cytoskeleton, cytoplasm becomes
dense, organelles tightly packed
- 2. cell surface
membrane
invaginates and
blebs form.
chromatin
condenses.
- 3. Nuclear envelop breaks
down, DNA breaks into
fragments, cell breaks into
vesicles
- 4. Vesicles taken up by
phagocytosis. cellular debris
disposed of and doesnt
damage other cells and
tissues. Quick process
- 1. enzymes breakdown cell
cytoskeleton, cytoplasm becomes
dense, organelles tightly packed
- Programmed cell death
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