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 & non-histone 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.

P

P

P

P

P

P

P

P

S

S

S

S

S

S

C

A

T

G

T

A

A

A T

T

G C

Specific base pairing arrangement (Chargaff’s Rule)

A-T : 2 hydrogen bondsC-G : 3 hydrogen bonds

Nitrogen bases attach to the sugar portion of the side (NOT the phosphate)

Strands run in opposite directions3’ --------------------------------------------------------

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 RNADouble helix strand Single strandThymine nucleotide base Uracil nucleotide baseDeoxyribose sugar Ribose sugarOnly I form Found in 3 formsFor long term storage of genetic information

Acts as messenger between DNA & ribosomes during protein synthesis.

Found in nucleus only 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 = nucleusPROCESS = 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 pairs1 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.