Summary
Summary Grade 12 IEB Life Science: DNA
- Course
- Grade 12 Life Science
- Institution
- Clifton School, Durban, KwaZulu Natal
In-depth summary notes on DNA, RNA, and all that happens in-between.
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By: belindac1973 • 7 months ago
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DNA - The code of lifeNucleic acids have the capacity to store information that controls cellular activity and
organism development. This is done through Protein synthesis. As enzymes too are
proteins, PS is important as they control the chemical process inside the cells.
Deoxyribonucleic acid
DNA was discovered by Wilkins and Franklin in 1950 when looking at Xray crystallography.
Crick and Watson analysed the X-ray data, and developed the idea of genetic replication.
A=T and C=T suggests that the sequences of bases in one strand will automatically be
determined. When the strands separate, each strand becomes a template for a
complementary new chain of DNA (ie. replicating). They proved that the double stranded
molecule could both replicate itself and carry genetic instructions. Crick and Wilkins won a
noble peace prize for their findings (Franklin did not because she dies).
Where is DNA found, how is it made up and what units make it up?
It is found in the nucleus, forming the chromosomes that make up the chromatin
(chromosomal material made up of DNA, RNA and histone proteins as found in a non-
dividing cell) network. It is coiled so they can all fit. Small amounts of DNA are found inside
the mitochondria and chloroplast. dan is a long, twisted ladder like structure that twists to
form from a 3-D double helix. DNA is a polymer made up of monomers called nucleotides.
Each is made of a a phosphate molecule, a deoxyribose sugar, and nitrogenous bases
(A,T,C or G) which are the fourdation of the genetic code.
How the helix is made up, how the pairs link and how the bases are classified:
The outer 2 strands of the DNA molecule are formed by a chai of alternating sugar/
phosphate links (strong bonds). The rungs of the ladder are formed by nitrogenous base
pairs that are held together by weak hydrogen bonds. These attach to the sugar
molecules. The shape and size of the nitrogenous bases differ, and due to this Thymine
can only bond with Adenine (double hydrogen bonds), and Cytosine only with Guanine
(triple hydrogen bonds). These bases are classified into 2 groups: Purines and
Pyrimidines. Purines are 2 fused rings of N, C and H atoms (ie. Guanine and Adenine).
Pyrimidines is only 1 ring of the same atoms, and is therefore much smaller (ie. thymine,
uracil and cytosine.) These are the same bases in all plants and animals. The sequencing
is what determines the genetic code.
The role of DNA and non-coding DNA:
DNA carries hereditary information that forms genes, codes for protein synethsis, and can
replicate so copies of information is passed onto daughter cells.
Less than 2% of DNA codes for protein synthesis. Protein-coding regions (exons) are
interrupted by non-coding regions (introns). Introns are known to form functional RNA
molecules.
Extraction of DNA
To successfully extract DNA, methods should release as much DNA as possible, minimise
degradation, and be efficient in terms of cost, time, labour and supplies. By using salt and
ethanol, its simple, time saving, and high yielding.
, Replication
The process of making new identical DNA molecules. During interphase the cells divide. It
ensures that the genetic code is passed on to each daughter cell during division. The enzyme,
DNA polymerase catalyses the process. The double helix unwinds, weak H bonds break, 2 strands
separate and a single chain of bases becomes exposed. Free nucleotides attach to corresponding
bases. A-T and C=G ensures the daughter cells to form the same sequence of bases. The 2
daughter cells twist, forming a double helix, winds itself around the histones, forming
chromosomes.
Mitochondrial DNA
mtDNA is a double stranded, ring shaped, found in all mitochondria. It comes from the
oocyte - inherited by mother. Has a genome of about 16 500 base pairs that code for
protein tRNA and rRNA. It is shorter, but genes are essential for coding for enzymes that
control cellular respiration. Through endosmosis, mitochondria contain their own circular
mitochondrial DNA. Prokaryotes are organisms that are not membrane bound (have a free
floating nucleus) and eukaryotic organisms have membrane bound organelles. During
fertilisation, the tail of the sperm (containing mitochondria) falls off, allowing only
chromosomes from the sperm to enter the ovum. Due to this, mitochondria is only passed
on from the mother. It can be used to establish direct maternal genetic lines. mtDNA can
mutate — substitution can take place; this is where a nucleotide is replaced by another
resulting in a marker. Profiles of these markers can be made to show if organisms are
closely related, or if any evolutionary differences have occurred.These markers can be
mapped, enabling researchers to trace lineages through females, and to track ancestry
*Mitochondrial Eve would be the first point of the network where everyone would meet if
everyone’s mitochondrial DNA was traced back.
They scrape tissue from the cheek cell and sent for mtDNA testing at any genetic
genealogy lab. The genetic code at different point is studied and compared to that of
another individual. Cambridge Reference Sequence (CRS)is the source of information of
human mitochondria. It can be used to reconstruct maternal-linked family lines, investigate
at forensic scenes where DNA has degraded, and to determine if siblings have the same
mother.
Ribonucleic acid
RNA is involved in protein synthesis. It is a polymer made up of nucleolides. It carries
instructions from DNA in the nucleus to ribosomes in order for the process of protein
synthesis to be undergone.
DNA RNA
Differences Thymine Uracil
Double helix Single uncoiled
Long Short
Deoxyribose sugar Ribose sugar
Similarities Have nucleotides made of 1 sugar, 1 phosphate and
nitrogenous bases
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