Download GENETICS Strand 3

Strand 3: Life at molecular,
Cellular & Tissue level
DNA, Genetics and Genetic Engineering
Structure & functions of the nucleus (revision):
Nuclear membrane: Envelope surrounding
nuclear material.
Nucleoplasm: Contents of the nucleus,
distribution of nutrients.
Nucleolus: Contains ribosomal RNA, is
associated with the coding of rRNA
during protein synthesis.
Nucleopore: Allows exchange of materials
between nucleoplasm & cytoplasm.
Chromatin Network: Chromosomal material
consisting of DNA together with histone & nonhistone proteins.
Nucleic Acids of the Cell:
•2 Types of nucleic acids are found:
DNA
RNA
•These nucleic acids are involved in coding of
genetic characteristics and allowing genetic
characteristics to be seen in individuals.
DNA
(DEOXYRIBONUCLEIC ACID)
•Structure was 1st envisioned by Watson & Crick in 1953
after various other researchers had developed their own
ideas (p230).
•The structure is a double strand which twists into a helix
shape.
•It consists of 2 polynucleotide chains, joined together by
hydrogen bonds between nucleotide bases.
•Deoxyribose names the sugar part.
•The nucleotide is completed by a phosphate part.
•A nitrogen part forms the different nucleotide bases.
•2 Types of nucleotide bases, PURINE & PYRIMIDINE.
•Only opposite bases can attach to each other.
•4 Nucleotide bases are found which are always
specifically paired up.
•PURINE bases = Adenine (A)
Guanine (G)
•PYRIMIDINE bases = Thymine (T)
Cytosine (C)
•Adenine & Thymine will bond together via 2 hydrogen
bonds.
•Guanine & Cytosine will bond together via 3 hydrogen
bonds.
P
P
S
C
G
S
P
P
S
A
T
S
P
P
S
P
T
A
S
P
A
T
G
C
T
A
Specific base pairing arrangement (Chargaff’s Rule)
A-T : 2 hydrogen bonds
C-G : 3 hydrogen bonds
Nitrogen bases attach to the sugar portion of the side (NOT
the phosphate)
Strands run in opposite directions
3’ -------------------------------------------------------- 5’
5’ --------------------------------------------------------- 3’
•Hydrogen bonds = The attractive force between the hydrogen
atom of one molecule and another, thus forming a non-covalent
bond (weak).
•Poly = lots / numerous
•Location of DNA = chromosomes in nucleus (nuclear DNA)
&
mitochondrions (mitochondrial DNA)
RNA
(RIBONUCLEIC ACID)
•A single polunucleotide chain.
•A vital component of protein synthesis, can occur in 3
forms =
1) Messenger RNA (mRNA) = produced during
transcription, involved in transferring genetic
information from DNA to ribosomes.
2) Ribosomal RNA (rRNA) = forms a major structural part
of ribosomes.
3) Transfer RNA (tRNA) = acts as an ‘adaptor’
molecule and carries amino acids to the
ribosomes to be inserted in the correct
sequence during translation.
•Ribose = sugar part
•Nucleotide chain completed by a phosphate part.
•Nitrogen part forms the different nucleotide bases.
•4 Nucleotide bases are always specifically paired.
•2 Types of nucleotide bases, PURINE & PYRIMIDINE.
•Onoly opposite bases can attach to each other.
•PURINE bases =
Adenine (A) & Guanine (G)
•PYRIMIDINE bases =
Uracil (U) &
Cytosine (C)
•Adenine & Uracil will bond together during certain phases of
protein synthesis.
•Guanine & Cytosine will bond together during certain phases
of protein synthesis.
Tabulated comparison between DNA & RNA
DNA
Double helix strand
Thymine nucleotide base
Deoxyribose sugar
Only I form
For long term storage of genetic
information
Found in nucleus only
RNA
Single strand
Uracil nucleotide base
Ribose sugar
Found in 3 forms
Acts as messenger between DNA &
ribosomes during protein synthesis.
Found in nucleus & cytoplasm
Similarities between DNA & RNA:
•Nucleotide bases
•Phosphate part
•Sugar part
•Sugar – phosphate bonds
HOMEWORK: Activity 3.1.5 p237 & 8
DNA Replication (copying) p238 - 239
WHEN = during cell division (mitosis)
WHERE = nucleus
PROCESS = 1 – Double strand splits when weak H-bonds
break.
2 – Single strand’s nucleotides collect matching
nucleotides from the nucleotide pool.
3 – New matching strands are constructed
and 2 new double strands that are
identical will result.
IMPORTANCE = ensures origin of cells with identical
DNA after cell division.
DNA Profiling (Fingerprinting) p240 - 242
•Because the arrangement and number of
nucleotides in the DNA of each person is unique,
they can be sequenced and compared in order to
identify specific people.
•This unique identification process is useful in solving
crimes, thus used in forensics.
•Specialist laboratories can do DNA profiling which
makes the cost of the process high.
•If samples are needed, some people might be
prohibited by their religion from giving a DNA sample.
•Many countries want a DNA database similar to the
one they have with fingerprints.
•It has happened that errors have been made and
innocent people have landed in prison.
Gel Electrophoresis
HOMEWORK: Activity 3.1.6 p245
Gene mutation:
Gene: a small portion of DNA which carries the genetic
code for the formation of a particular trait / characteristic; it
also carries the code for proteins.
Mutation: any change that occurs which creates a
difference in the order of nucleotide bases in a gene.
Fatal mutation: causes the death of the organism / s.
Useful mutation: will help the organism to survive and be
biologically viable, thus it will reproduce more and the
offspring will inherit the useful mutation.
The following images may be disturbing!!
DNA Sequencing:
•The phylogeny or relationships in development of different
organisms can be determined by DNA sequencing.
•The organisms in question will have their DNA
investigated and compared.
•If a large number of codon sequences match, then the
organisms are more closely related, in terms of
development on Earth.
•With fewer matches, the organisms are not closely
related.
•Compare DNA profiling of human DNA sequences in
forensics.
Recombinant DNA technology:
•Using two sets of DNA and recombining them to get a
desired result.
•Most common example is the use of E. coli bacteria in the
production of human insulin to treat diabetes.
•In the past, animal insulin was used (pigs, cows etc.)
which did not always have the desires result.
PROTEIN SYNTHESIS: p242 - 244
•A complex anabolic process where genes control the
precise structure of the proteins that are made.
•DNA supplies the master plan in code form (A, T, G, C).
•The types and order of the nucleotide bases supply the
code.
•The code is formed by nucleotide
bases, in groups of 3, called a codon.
•An opposite matching group of
3 is called an anti-codon.
STEP 1: TRANSCRIPTION
•The DNA never leaves the nucleus, thus something else
must perform the construction of the proteins.
•mRNA is created by using the code contained in the DNA
strand.
•mRNA takes this code to the ribosomes outside the
nucleus.
STEP 2: TRANSLATION
•tRNA exists in the cell with all possible combinations of the
code obtained from the DNA.
•The code is arranged in groups of 3, opposite to those on
the mRNA, thus the anti-codon.
•Each specific anti-codon can only attach to a specific
matching amino acid.
•tRNA collects amino acids from the amino acid pool in the
cell and transfers those amino acids to the mRNA waiting
at the ribosomes.
•The order of the code on mRNA determines the order in
which the amino acids will be laid down.
•The order of amino acids will determine the type of protein
that is made.
•Once amino acids are deposited, tRNA breaks loose to
collect another.
•The amino acids will bond together with peptide bonds to
create the correct length of protein (polypeptide).
Functions of Protein:
1.Important building blocks of muscles, skin
(collagen), nails & hair (keratin & melanin),
connective tissue (collagen).
2.Important components of cell membranes.
3.Enzymes in chemical reactions.
4.Hormones (not all).
5.Anti-bodies of the immune system.
Chromosomes:
•Chromosome consists of 2
chromatids held together by a
centromere.
•2 chromatids = 1 chromosome
•92 chromatids = 46 chromosomes
•Chromosomes always found in pairs (homologous
pairs).
•Human chromosomes = 23 pairs
22 autosome pairs
1 gonosome pair
(sex chromosome) p248
•Homologous chromosomes = pair of identical
chromosome, one from mother & other from father.
•Haploid (n) = half the usual number of chromosomes,
usually the condition of the reproductive cells, sperm &
egg (gametes).
•Diploid (2n) = the total number of chromosomes,
found in somatic cells.
•Visualized in a Karyotype.