PROTEIN SYNTHESIS
LOCATION OF
PROSTATE GLAND
Located under the bladder and in
front of the rectum, the prostate
gland secretes substances into
the semen as the fluid passes
through ducts leading from the
seminal vesicles into the urethra.
benign prostatic hypertrophy (see
p r o -
s ta t ic h y p e rtro p h y , b e n ig n
)
and
p ro s ta t it is
(inflammation of the prostate).
p ro s ta tic h y p e rtro p h y , b e n ig n
An increase in size of the
p ro s ta t e g la n d
,
w hich is most common in men over
the age of
5 0
.The cause is unknown.
SYMPTOMS
The enlarging prostate compresses and
distorts the
u re th ra
,
impeding the flow
of urine from the bladder (known as
outflow obstruction). This causes symp-
toms of
p ro s t a t is m
,
such as frequent
urination and dribbling at the end of
the urine stream. There may also be
incontinence (see
in c o n t in e n c e , u rin a ry
) .
Eventually the bladder is unable to expel
all the urine (see
u r in a r y re t e n tio n
)
and
becomes distended, causing swelling,
w hich may be painful. The bladder’s
inability to empty completely each time
urine is passed may lead to
u r in a r y tra ct
in f e c t io n s
.
K id n e y f a ilu re
may occur as a
complication of outflow obstruction.
DIAGNOSIS AND TREATMENT
Prostate enlargement is detected by a
r e c -
tal e x a m in a tio n
.
Tests may include
b lo o d
te s ts
,
u ltra s o u n d s c a n n in g
,
and recording
the
strength
of urine
flow. Tests
to
exclude
p ro s ta t e c a n c e r
as a cause of
enlargement may be needed.
M ild cases do not require treatment, but
severe abdominal pain due to blockage
of the urine flow needs immediate
treatment. Men with a severely enlarged
prostate
usually
require
p ro s ta te c to m y
(surgical removal of the prostate gland).
Alternatively,
a lp h a - b lo c k e r d ru g s
may be
given to improve the flow of urine or
a n tia n d ro g e n d ru g s
may be used to coun-
teract the effects of testosterone.
p ro sta tis m
Symptoms that arise from the enlarge-
ment of the prostate gland (see
p ro sta te,
e n la rg e d
) due to its compression and dis-
tortion of the
u re th ra
,
w hich impedes
the flow of urine from the bladder
(outflow
obstruction).
Symptoms
of
prostatism often include frequent u ri-
nation (see
u rin a tio n , f re q u e n t
) ,
getting
up at night to urinate, delay before the
urine stream starts, dribbling at the end
of the stream, and incontinence (see
in c o n t in e n c e , u rin a ry
).
p ro s ta titis
Inflammation of the
p ro s ta t e g la n d
,
usu-
ally affecting men aged between
3
0
and
5
0
. It is often caused by a bacterial
infection that has spread from the
u r e -
t h ra
.
The presence of a urinary
c a t h e t e r
increases the risk of prostatitis.
The main symptoms of prostatitis are
fever, flulike symptoms, and pain in the
lower back. There may also be pain
around the rectum, w hich is particular-
ly troublesome on passing faeces. Diag-
nosis is made by
re c ta l e x a m in a tio n
and
tests on urine samples. Treatment is
with
a n t ib io t ic d r u g s
.
The condition may
be slow to clear up and tends to recur.
p ro s t h e s is
An artificial replacement for a missing
or diseased part of the body; for exam-
ple, artificial limbs (see
lim b , a rtific ia l
) ,
heart valves (see
h e a rt-v a lv e s u r g e r y
), or
glass eyes (see
eye, a rtific ia l
) .
p ro s th e tic s , d e n ta l
The branch of
d e n t is t ry
concerned with
the replacement of missing teeth and
their supporting structures. It includes
d e n t u r e s
,
overdentures (semipermanent
fittings over existing teeth), crowns
(see
c ro w n , d e n t a l
) ,
and bridges (see
b r id g e , d e n t a l
).
p ro te a s e in h ib ito rs
A type of
a n tire tro v ira l d ru g
that is used
to delay the progression of
H IV
infec-
tion. (See also
A ID S .
)
p ro te in s
Large molecules consisting of hundreds
or thousands of
a m in o a c id s
linked into
long chains. Proteins may be combined
w ith sugars (glycoproteins) and
lip id s
(lipoproteins).
There are two main types of proteins.
The first type,
fibrous
proteins,
are
insoluble and form the structural basis
of many body tissues. The second type,
lobular proteins, are soluble and in-
clude all
e n z y m e s
,
many
h o rm o n e s
,
and
some blood proteins, such as
h a e m o g lo -
b in
.
In addition, the
c h ro m o s o m e s
in cell
nuclei are formed from proteins linked
w ith
n u c le ic a c id s
,
and cell walls are
formed in part from proteins linked
w ith lipids (see cell).
Dietary proteins are needed mainly in
order to supply the body with amino
acids.
Ingested
proteins
are
broken
down in the digestive system to form
amino acids, w hich are then absorbed
and rebuilt into new body proteins (see
p ro t e in s y n t h e s is
) .
p ro te in s y n t h e s is
The formation of protein molecules
through the joining of
a m in o a c id s
.
Pro-
teins provide many of the structural
components and the enzymes that pro-
mote biochemical reactions in the body,
so their manufacture is essential for
development and growth.
Different cells manufacture various
ranges of proteins. The instructions for
these processes are held by the
D N A
(deoxyribonucleic acid) in the nucleus
of the cell. Protein synthesis starts when
a
g e n e
(a particular length of DNA) acts
as a template to form a strand of a sub-
stance called messenger
R N A
.
Like DNA,
RNA consists
of a string
of build-
ing blocks, w hich are called nucleotide
bases; the sequence of bases provides
the genetic code for making whichever
protein is required.
The
strand
of
messenger
RNA
passes out of the cell nucleus, where it
is then decoded (see the illustrated box
overleaf) to form a polypeptide chain (a
string of amino acids). Several poly-
peptide chains may be combined to
form one protein molecule.
The rate of protein synthesis is regu-
lated by adjustments in the amount of
messenger RNA formed in the nucleus
of the cell. Highly complex mechanisms
operate in order to ensure that the cell
manufactures the correct type of pro-
teins, in the required quantities, and at
exactly the right time.
P
633
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