Unit 4 - Topic 1: Dna, Genes and Continuity of Life

Question 1

What is DNA

Answer 1

• Deoxyribonucleic acid
• Contains the genetic information of all living organisms, and instructions for growth, function, development and reproduction.
• It is a double stranded molecule that occurs bound to proteins (histone) in the chromosomes of the nucleus
• ## The double strands are held together by hydrogen bonds, allowing for coiling of the DNA

Question 2

Recall the structure of DNA

Answer 2

• nitrogenous base
• phosphate
• sugar

Question 3

Explain the role of helicase and DNA polymerase in the process of DNA replication.

Answer 3

There are two crucial enzymes necessary for DNA replication; Helicase and DNA polymerase.
Helicase is responsible for unwinding the DNA double helix via the breaking of weak hydrogen bonds (replication fork begins) resulting in a single stranded DNA.
The exposed nuclotides of the DNA strand are attacthed according to base pairing rules by the enzyme DNA polymerase to the new complementary strand.
Nucleotides are added to the complementary strand in the 5’-3’ direction

Question 4

Homologous Chromosomes

Answer 4

Homologous chromosomes are chromosomes pairs in which one was inherited from the gg and one from the sperm. (thats why referred to diploid - they have 2 copies of each chromosome) they have the same shape and size and position of the centromere.

Question 5

Explain the role of Homolgous Chromosomes in Meiosis 1

Question 6

Explain the role of Homolgous Chromosomes in Meiosis 2

Question 7

Demonstrate how the process of independent assortment and random
fertilisation alter the variations in the genotype of offspring.

Answer 7

During fertilisation, 1 gamete from each parent combines to form a zygote. Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA. This produces a unique combination of genes in the resulting zygote.

Question 8

Independent Assortment

Answer 8

Each daughter cell can receive a copy of either chromosome from a pair and each copy may have undergone crossover and have genes from other chromosomes.

Question 9

Define Genome

Answer 9

the complete set of DNA (genetic material) in an organism required for growth and development.

Question 10

Define gene

Answer 10

The basic unit of heredity passed from parent to child. Genes are made up of sequences of DNA and are arranged, one after another, at specific locations on chromosomes in the nucleus of cells.

Question 11

Genes

Answer 11

Genes include non coding and coding DNA.

Question 12

Coding (exons) DNA

Question 13

Non-Coding DNA (functional RNA, centromeres, telormeres and introns)

Question 14

Proteins Synthesis

Answer 14

Inside each cell, catalysts seek out the appropriate information from this archive and use it to build new proteins — proteins that make up the structures of the cell, run the biochemical reactions in the cell, and are sometimes manufactured for export. Protein synthesis under goes to major stages; transcription and translation.

Question 15

Transcription

Answer 15

The goal of transcription is to make a RNA copy of a gene’s DNA sequence. For a protein-coding gene, the RNA copy, or transcript, carries the information needed to build a polypeptide (protein or protein subunit).

Question 16

Translation

Answer 16

In this stage, the mRNA is “decoded” to build a protein (or a chunk/subunit of a protein) that contains a specific series of amino acids.
Transfer RNAs, or tRNAs, are molecular “bridges” that connect mRNA codons to the amino acids they encode. One end of each tRNA has a sequence of three nucleotides called an anticodon, which can bind to specific mRNA codons. The other end of the tRNA carries the amino acid specified by the codons.
There are many different types of tRNAs. Each type reads one or a few codons and brings the right amino acid matching those codons.

Question 17

Gene Expression

Answer 17

Different cell types “turn on” different genes, allowing different proteins to be made. This gives different cell types different functions. Once a gene is expressed, the protein product of that gene is usually made.This mostly occurs via the transcription of RNA molecules that code for proteins or non-coding RNA molecules that serve other functions.

Question 18

Phenotypic Expression of Genes

Answer 18

• During transcription/translation

Answer 19

Differential gene expression means different gene expression and is the process where different genes are activated in a cell, giving that cell a specific purpose that defines its function. When a stem cell has differentiated, it becomes a somatic cell with a specific phenotype.

Gene expression is controlled by transcription factors and necessary in cell differentiation and tissue formation, along with morphological development. Transcription factors do this by binidng to distinct regions of DNA and determining when genes are activated.

Question 20

A transcription factor that affects morphology

Answer 20

HOX GENE
a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of ‘position’, ensuring that the correct structures form in the correct places of the body.

Question 21

Transcription factors that affects cell differentiation

Answer 21

SEX DETERMING REGION Y
is necessary for male sex determination in mammals. SRY initiates the cascade of steps necessary to form a testis from an undifferentiated gonad.

Question 22

Gene and Chromosome Mutations

Answer 22

Mutations can occur during:
- DNA Replication: Insertion or deletion.
An insertion mutation occurs when an extra nucleotide is added to the DNA strand during replication. This can happen when the replicating strand “slips,” or wrinkles, which allows the extra nucleotide to be incorporated.
A deletion mutation occurs when a wrinkle forms on the DNA template strand and subsequently causes a nucleotide to be omitted from the replicated strand
- Non disjunction: failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of chromosomes. (trisomy or monosomy)
- damage of mutagens: is a chemical or physical agent capable of inducing changes in DNA called mutations. Examples of mutagens include tobacco products, radioactive substances, x-rays, ultraviolet radiation and a wide variety of chemicals.

Question 23

How does non-disjunction lead to aneuploidy

Answer 23

Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have a normal complement of 23 chromosomes. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1.

Question 24

How can inherited mutations alter variations in the genotype of offspring.

Answer 24

Mutations can introduce new character which means new genotype. Mutations can alter certain traits by absolutely silencing a particular gene thus producing genotypic variation. Mutations can also produce different products from similarly sequenced mRNA transcripts.

Question 25

Inheritance

Answer 25

autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, mitochondrial - refer to paper example.

Question 26

Process of recombinant DNA

Answer 26

The first commercial healthcare product derived from rDNA was human insulin. Today, it is successfully applied to make new antibodies, vaccines (e. g. for Hepatitis B) and different protein production systems, for instance for insulin and human growth hormone.​​
Steps:
1. Isolation of genetic material
2. Cutting of DNA at specific locations (restriction enzymes)
3. Joining of DNA fragments by ligation and homopolymer tailing (DNA ligase)
4. Insertion of DNA into the host cell (plasmid vector)
5. Selection and screening of transformed cells
The last step can be achieved by an immunological method or nucleic acid hybridization, blue-white screening or insertional inactivation.

Question 27

DNA sequencing

Answer 27

to map species’ genomes and
DNA profiling to identify unique genetic information

Question 28

Explain the purpose of polymerase chain reaction (PCR) and gel
electrophoresis

Answer 28

PCR is a very sensitive technique that allows rapid amplification of a specific segment of DNA. PCR makes billions of copies of a specific DNA fragment or gene, which allows detection and identification of gene sequences using visual techniques based on size and charge.
Gel Electrophorisis is Used to separate mixtures of DNA, RNA, or proteins according to molecular size. In gel electrophoresis, the molecules to be separated are pushed by an electrical field through a gel that contains small pores.