Re: Jewish Genes
- From: Mirelle <mirellebonte@xxxxxxxxx>
- Date: Fri, 8 Feb 2008 17:54:48 -0800 (PST)
On Feb 8, 10:00 am, jgarbuz <jgar...@xxxxxxxxxxx> wrote:
Jewish Genes
"Jewish Genes", Huh?
DNA is made of MATTER, not Biblical fairy tales.
DNA
Structure of an organism
DNA is the common name for Deoxyribonucleic acid, the chemical of
life. This nucleic acid is made of long chains of nucleotides, which
are complex molecules present in the nucleus of all cellular forms of
life and many viruses, and in the cytoplasm of single celled bacteria,
which do not have a nucleus. DNA carries along its length a series of
coded chemicals called genes, which give instructions for passing on
hereditary characteristics, such as leaf shape, claw length, hair or
eye colour as well as susceptibility to some diseases.
Each nucleotide consists of:
1. A sugar with five carbon atoms, either:
(a) Deoxyribose, a sugar used by DNA, with a hydrogen atom attached to
its carbon atom number 2' (referred to as the two prime carbon atom; '
or prime is the first sub division or symbol marking it).
or
(b) Ribose, a sugar used by RNA (a single strand ribonucleic acid
which translates the coded messages) and with a hydroxyl group atom
attached to the 2' carbon.
2. One of three phosphates with four oxygen atoms, two of which are
negatively charged:
Attached to the 5' carbon atom of the deoxyribose sugar and covalently
to the 3' of the next. (One electron from each atom joins the two
together).
3. A base:
One of four kinds of nucleobases (a base). A base, is a ring structure
containing nitrogen and is attached to the 1' carbon atom of the
deoxyribose sugar.
The four bases used by DNA are:
Adenine (A) and Guanine (G) which are purines. Thymine (T) and
Cytosine (C) which are pyrimidines.
The four bases used by RNA are:
Adenine (A) and Guanine (G) which are purines. Uracil (U) and Cytosine
(C) which are pyrimidines.
DNA composition
Pairs of DNA molecules, each only one millionth of a millimetre long,
containing chromosomes with encoded genes along them take the shape of
a right handed twisting double helix, an elegantly simple structure
that resembles gently twisted ladders. The side rails of the ladder
are made of alternating molecules of deoxyribose sugar and phosphates,
going down one side of the strand and up the other. The rungs on the
inside consist of hydrogen bonds, joining the bases in a particular
sequence across the strands. The bonds are antiparallel, with a spare
phosphate at opposite ends of each strand. The hydrogen on a base is
attracted to the carbon on a sugar, whereas phosphates, being
negatively charged, would repel each other if they were opposite each
other on the inside of the helix.
DNA phosphate
DNA Deoxyribose sugar
DNA section showing gene ACT on the descending strand and gene AGT on
the ascending strand
DNA strands, when viewed through an electron microscope, are read from
the 5' carbon atom to the 3' carbon atom on the descending strand, and
3' to 5' on the ascending strand. Each chromosome is a very long piece
of DNA with many genes encoded along its length. It is twisted, looped
and wound round itself, attached to a protein to maintain its shape,
then two sets are twisted into the double helix shape. The human
chromosome number 1 is 10 micrometres long, but has 7 cms of DNA
inside it.
There are three forms of DNA:
1. The A or dehydrated (dry) form, used in crystallography. This
twists in a right handed helix and has 11 base pairs per turn.
2. The B or wet form, 2 nanometres wide, twisting in a right handed
helix, with 10 base pairs per turn.
3. The Z form, similar to B but twisting in a left handed helix.
Sometimes created by mutation.
By understanding the structure of the molecule clues can be gained
about how it functions. Because each base within a rung of the DNA
ladder is always paired with the same complimentary base, one half of
the molecule can serve as a template for the construction of the other
half. The length of DNA in a single cell is approximately 1.7 metres
wound tightly round itself. Each cell in the body has a similar length
of DNA and all the DNA in the body would reach to the moon and back
6000 times.
Double Helix
This diagram shows the two phosphate-sugar chains held together by the
pairs of bases forming the rungs of the DNA ladder. The vertical line
shows the axis.
The nucleotides in DNA contain the bases adenine (A), guanine (G),
cytosine (C) and thymine (T). In nature genetic encoding is carried
out with these four building blocks. Each base will only pair up with
one other base on the strand by means of hydrogen bonds; adenine with
thymine or cytosine with guanine. There are three types of hydrogen
bonds: O-H-N, O-H-O, N-H-N. (O is oxygen, N is nitrogen, H is
hydrogen). The bases are attracted because the hydrogen atom on one
base is attracted to either the oxygen or nitrogen atom on the other,
thus allowing hydrogen bonds to be formed. Two hydrogen bonds join A+T
and T+A; three hydrogen bonds join C+G and G+C. Thus the sequence of
the bases along each single strand can be deduced from that of its
partner. This complimentary pairing explains how identical copies of
parental DNA can be passed on to two daughter cells.
Thymine and Adenine
Cytosine and Guanine
During cell division, the DNA helix chemically "unzips", and two new
strands are formed from the half-ladder templates. The precise
sequence of nucleotides (sugar, phosphate and base) in the DNA ladder
directs the manufacture of proteins and determines the identity of a
living organism and makes the cells work. Each type of cell, such as
kidney or skin, will only use the specific instructions needed for it
to function.
Each chromosome is a very long molecule of DNA with many genes along
its length, providing a set of instructions for making an organism.
These instructions are called the genome. The number of bases can vary
from a thousand to a million. A sequence of three bases, such as A C
T, C A G, T T T, along the strand makes up a gene, each group of three
represents the code for one of twenty amino acids, which in due course
forms part of a protein molecule, which provides the structure of
cells and tissues. Each group of three is a codon. There are 64 known
codons, with 3 stop or nonsense codons marking the end of the
sequence. It is estimated that 3 billion base pairs of A T C G make up
the human genome, less than 5% being genes, the function of the rest
is not known at present. Each individual has a different arrangement
of these letters in their genetic code, thus it is very unlikely that
two humans or organisms will be exactly identical. The purpose of more
than 30,000 genes has so far been established.
Each cell in the human body contains two complete sets of 22 numbered
chromosomes plus X and Y, making 46 in total. The arrangement of the
chromosomes in a cell is called a karotype. The largest chromosome is
number 1 and the smallest is number 22, plus sex chromosomes X and Y,
females having two X and males X and Y. In the laboratory white blood
cells are generally used to study chromosomes, which are separated
using enzymes. When stained they are seen to have a waist like band at
the centre, called a centromere, and distinctive black and white bands
showing the different amounts of bases A and T compared with bases G
and C in each and so they can be identified. Chromosomes are divided
at the centromere into a long and short arm, the short arm being
called petit or p and the long arm being called q. The regions on the
chromosome are numbered from the centromere for identification
purposes. Regions are specifically numbered up or down from the
centromere, so a specific part of a chromosome can be pinpointed using
a code.
For example: A female with an abnormality on the long arm of
chromosome 9 would be written as XX9q12.1
XX represents female
9 is the chromosome number
q is the long arm
12.1 is the region
Whereas a male with the same abnormality would be written as XY9q12.1
as XY represents male.
XY represents male
9 is the chromosome number
q is the long arm
12.1 is the region
If a gene is missing from the short arm of chromosome 6, it would be
identified as 6p-.
6 is the chromosome number
p is the short arm
- means a gene is missing
Each chromosome has a particular sequence of genes. In humans
chromosome number 11 has 2093 genes, with 134,978,784 bases.
Chromosome number 22 has 288 genes, with 49,476,972 bases.
Different species have a different number of chromosomes.
Human - 46
Fruit fly - 8
Fern - approx. 1200
Dog - 78
Earthworm - 36
Chicken - 78
Carp - 104
The reproductive cells, the egg and the sperm, each contain only 23
single chromosomes, formed by the process of meiosis. During
reproduction these join together to form a new cell with one set of
chromosomes from each parent. In this way, each offspring has
characteristics from each parent, but is not identical to either. The
DNA in this cell then splits and replicates millions of times by the
process of mitosis until a viable new offspring is formed. One human
chromosome contains 150 x 106 nucleotide pairs and these are copied at
50 base pairs per second. Replication can occur at several points on
the chromosome, thus the whole process takes about one hour. If
replication took place at only one point it would take a month.
New nucleotides are constantly being made within the cell nucleus.
During replication the strand splits at several places where the G C
pairs are weakest connected by two hydrogen bonds. When a cell is
ready to divide the enzyme DNA helicase untwists the helix to form a Y
shape, called a replication fork. The enzyme DNA polymerase travels
from the join of the replication fork down the leading strand in the
3' to 5' direction, reading the nucleotide sequence. To maintain the
antiparallel form of the DNA, with a phosphate at the 5' end, the DNA
polymerase then attaches new, corresponding nucleotides to the leading
strand in the 5' to 3' direction. New nucleotides cannot be attached
at the 3' end of the second or lagging strand, as this would upset the
antiparallel form leaving a phosphate at the wrong end of the strand.
Sections of DNA called Okazaki fragments are therefore made in the
nucleus of the cell to combat this. When long enough sections have
been made they become attached to each other and to the lagging strand
in the 5' to 3' direction by the enzyme DNA ligase. Two new strands of
DNA have now been assembled.
Mitosis is the process by which most cells in the human body are
replicated. During replication a duplicate is made for each
chromosome, doubling the number in the cell to 92, so they become X
shaped by joining at the central waist like area called the
centromere. This is attached to microtubules which, during cell
division, pull the chromosomes to opposite ends of the cell. The cell
divides in the middle having created two identical daughter cells each
with 46 chromosomes.
Meiosis is the process of replication by which egg cells are produced
in the female ovaries and sperm cells are produced in the male testes.
This involves two sets of cell division. The first part of the process
is similar to mitosis as stem cells produce two identical cells, each
with 46 chromosomes. However, some of these then split again, without
replicating the chromosomes, resulting in four cells each with only 23
chromosomes. During meiosis the chromosomes crossover twice to produce
different gene combinations in each egg or sperm and this process
takes three weeks to complete. In human males 200,000,000 sperm are
made each day, but in females only one viable ovum is made each
month.
Also in the nucleus of the cell is the chemical RNA (Ribonucleic acid)
composed of adenine, guanine, uracil and cytosine. RNA is divided into
several classes, each having a different function within the cell.
During the making of a protein a unit of three coded bases on the DNA
unwinds and passes the code on to a messenger molecule of RNA.
Carrying the copied code this then moves out of the nucleus into the
cytoplasm of the cell where it is copied into an amino acid and this
joins with more amino acids to form a protein.
Proteins are polymers which can be composed of up to 20 different
amino acids. These are arranged in a string along the protein and can
be in a complex pattern. The sequence of the amino acids and the
function of the protein is determined by the genetic code. There are
many different types of protein performing tasks such as:
Storage, transport, hormonal, receptor, contractive, defensive,
enzymatic.
Thus we see that all organisms are made up of many chemicals which,
when organised, have specific ways of working together, as in DNA.
These chemicals came from the primordial swamps and are constantly
evolving.
http://www.ba-education.demon.co.uk/for/science/dnabiology1.html
Mirelle
.
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