Nucleic Acids, Protein Synthesis & Cell Division

Question 1

True or false;
Nucleic acids are organic

Answer 1

True

Question 2

Describe the structure of nucleotides

Answer 2

• has a five carbon sugar, nitrogenous base and phosphoric acid
• Those containing ribose, are called ribonucleic acid, and those containing deoxyribose called deoxyribonucleic acid
• Each nucleic acid contains four bases two are purines, and two are pyrimidines
• Purines; Adenine, Guanine
• Pyrimidines; Thymine, Cytosine, Uracil (in place of thymine in RNA)
• Phosphoric acid gives the nucleic acids their acid character

Question 3

Describe the process of formation of a nucleotide

Answer 3

• A pentose sugar is joined to phosphoric acid and then to a nitrogenous base in a condensation reaction in which two water molecules are lost
• The phosphate group is joined at C-5 and the nitrogenous base is joined at C-1

Question 4

Describe the structure of DNA according to Watson & Crick

Answer 4

• DNA is made up of two polypolynucleotide chains
• The nucleotides have nitrogenous bases such as Adenine and Guanine (purines) and Cytosine and thymine (pyrimidines)
• They also have the pentose sugar deoxyribose
• Phosphoric acid is also a constituent of nucleotides situated on C-5 of the pentose sugar
• There is complementary base pairing between the nitrogenous bases which are bonded by hydrogen bonds
• Adenine is joined by two hydrogen bonds to Thymine while guanine is joined by three hydrogen bonds to cytosine.
• The nucleotides are joined by phosphodiester bonds
• Thus DNA has a sugar-phosphate backbone
• The two polynucleotide chains run in opposite directions (anti-parallel). One in the five prime to three prime direction, and the other, in the three prime to five prime direction
• DNA has a double helix structure
• The hydrogen bonds easily break and form for replication
• The width between the backbones is equal to the width of a base pair

Question 5

Describe the semi conservative theory

Answer 5

From the original DNA strand, two similar copies of DNA are formed containing half the original DNA and half being the newly formed polynucleotide chain

(The old chains are templates for the new DNA strands)

Question 6

Describe the process of DNA replication

Answer 6

• The enzyme DNA Helicase catalyses the unzipping of the two polynucleotide chains, exposing the nitrogenous bases on each chain
• Each polynucleotide chain serves as a template for formation of a new DNA strand
• Single-stranded binding protein stabilizes the single strands and prevents them from recoiling
• Topoisomerase enzyme catalyses the reduction in tension in the chain as unwinding continues
• RNA primase enzyme catalyzes the addition of an RNA primer, which initiates the process
• DNA polymerase catalyzes the removal of the RNA primer and addition of nucleotides to the exposed bases following the complementary base pairing rule
• The new polynucleotide chain is synthesized in the five prime to three prime direction
• It also proofread the newly formed DNA to remove any errors
• It repairs the DNA where necessary
• DNA ligase enzyme joins the Okazaki fragments together on the lagging strand

Question 7

Give the similarities between the lagging strand and the leading strand

Answer 7

• both are templates for DNA replication
• Both form half of the new DNA

Question 8

Give the differences between the leading strand in the lagging strand

Answer 8

LEADING
- runs in the three prime to five prime direction
- The polynucleotide formation is continuous
- Okazaki fragments are absent
- DNA ligase is not involved

LAGGING
- runs in the five prime to three prime direction
- The polynucleotide formation is discontinuous
- Okazaki fragments are present
- DNA ligase is involved

Question 9

What are the adaptations of DNA to its functions?

Answer 9

• strong covalent phosphodiester bonds for stability
• Anti-parallel for complementary base pairing
• Double stranded for stability
• Double helix to protect the bases and hydrogen bonds
• Long to store much information
• Double helix structure, compact to fit in the nucleus
• Base sequence allows information to be stored
• Double stranded for replication to occur semi conservatively
• Complementary base pairing for identical copies to be made
• Weak, hydrogen bonds, enable unwinding of stands to occur
• Many Hydrogen bonds for stability

Question 10

Why is DNA confined to the nucleus?

Answer 10

• to prevent alteration by chemical reactions in the cytoplasm
• It is too large to fit through the nuclear pores

Question 11

What is the use of ribosomes in proteins synthesis?

Answer 11

They are a point of anchorage for the tRNA and mRNA molecules

Question 12

What is transcription?

Answer 12

This is the mechanism by which the base sequence of a section of DNA representing a gene is converted into the complementary base sequence of mRNA

Question 13

Where does transcription occur?

Answer 13

It occurs in the nucleus

Question 14

Where does translation occur ?

Answer 14

Cytoplasm, Ribosome

Question 15

What is translation?

Answer 15

This is the mechanism by which the sequence of bases in an mRNA molecule is converted into a sequence of amino acids in a polypeptide chain

Question 16

What is the importance of transcription?

Answer 16

1. DNA is too large to fit through the nuclear pores yet mRNA being small can readily exit the nucleus
2. DNA contains many codes that aren’t always needed at a given time so mRNA only carries the code needed to make specific proteins

Question 17

Describe the process of transcription

Answer 17

[start by defining transcription]
[State where proteins synthesis happens, and where transcription happens and why]

• The DNA double helix unwind by breakage of the relatively weak hydrogen bonds between the bases of the two strands
• Single strands of DNA are exposed
• One strand is selected as the template strand for the formation of a complementary single strand of mRNA
• Under the influence of RNA polymerase, and according to the rules of base pairing between DNA and RNA, that is A & U and G & C the mRNA molecule is formed through linking of free nucleotides
• When the mRNA molecules have been synthesized, they leave the nucleus via the nuclear pores, and carry the genetic code to the ribosomes for protein synthesis
• When sufficient numbers of mRNA molecules have been formed from the gene, the RNA polymerase molecule leaves the DNA and the two strands zip up again, reforming the double helix

Question 18

Describe the process of translation

Answer 18

1. Binding of mRNA to ribosome
2. Amino acid, activation, and attachment to tRNA
3. Polypeptide, chain initiation
4. Chain elongation
5. Chain termination
6. Fate of the polypeptide chain

Question 19

Define cell cycle

Answer 19

The cell cycle is the sequence of events which occurs between one cell division, and the next.

Question 20

State the constituents of interphase in cells

Answer 20

• G1 phase
• Synthesis phase
• G2 phase

Question 21

Describe growth phase 1 of the cell

Answer 21

• intense cellular synthesis of new cell organelles
• Highly metabolically, active
• Rapid cell growth
• Overall cell mass increases

Question 22

Describe the synthesis phase of the cell

Answer 22

• DNA replication (only in eukaryotes)
• Synthesis of histones
• Each chromosome exist as two chromatids

Question 23

Describe growth, phase 2 of the cell

Answer 23

• intense cellular synthesis
• Centrioles replicate
• Mitochondria and chloroplasts divide
• Energy stores increase
• Overall cell size increases
• Mitotic spindle begins to form

Question 24

What is meant by the term mitosis ?

Answer 24

This is the formation of two identical daughter cells, which are diploid like the parent cell.

Question 25

Describe the events that take place during mitosis in animal cells

Answer 25

1. Prophase - Chromosomes shorten, thicken, and become visible - In animal cells, centrioles move to opposite poles of the cell - Aster formation - The nucleolus disappears - The nuclear envelope disappears - A spindle begins to form 2. Metaphase - Spindle fibers fully formed - Chromosomes line up along the equator of the spindle - Spindle fibers, attach to the centromere and contract, pulling the chromosomes apart 3. Anaphase - centromere split into two and spindle fibers pull daughter centromeres to opposite poles - Separated, chromatids are pulled along behind the centromeres 4. Telophase - chromatids reach the poles of the cell lengthen and uncoil to form chromatin again - Spindle, fibers disintegrate - Centrioles replicate - The nuclear envelope reform is around chromosomes at each pole - Nucleolus reappears 5. Cytokinesis/ cell division - cell organelles are evenly distributed towards the two poles of the cell - The cell surface membrane begins to invaginate towards the region, previously occupied by the spindle equator - Furrow is formed around the outside surface of the cell - The cell surface membrane in the furrow eventually join up and completely separate into two cells

Question 26

Define meiosis

Answer 26

This is a form of nuclear division in which the chromosome number is halved from the diploid number to the haploid number

Question 27

Describe the process of meiosis

Answer 27

1. Prophase one - chromosomes, shorten, thicken, and become visible - Homologous chromosomes pair up in a process called synapsis - Each pair is called a bivalent - The two chromosomes are joined at several points, called chiasmata - Crossing over, occurs at the chiasmata between non-sister chromatids - This leads to new gene combinations - Centrioles migrate to the poles - Nucleolus and nuclear envelope disappear - Spindle fibers begin to form 2. Metaphase one - The by valance are arranged at the equator of the spindle attached by the centromeres - They are randomly assorted along the equator 3. Anaphase one - spindle, fibers, pull homologous chromosomes by the centromeres towards opposite poles of the spindle - The chromosomes are separated into two haploid sets, one at each end of the spindle 4. Telophase one - homologous chromosomes arrive at the opposite poles - Is crossing over has occurred the chromatids are not genetically identical - Spindle fibers disappear - Nuclear envelope reform at each pole - Cleavage occurs 5. Prophase two - The nucleolus and nuclear envelope disappear - Chromatids, shorten, and thicken - Centrioles if present move to opposite poles of the cell - New spindle fibers start to appear 6. Metaphase two - chromosomes line up separately around the equator of the spindle 7. Anaphase two - centromeres divide - spindle fibers pull the chromatids to opposite poles by the centromeres 8. Telophase two - four haploid daughter cells are formed - Chromosomes uncoil, lengthen, and become indistinct - Spindle fibers disappear - Centrioles replicate - Nuclear envelope reform - Cleavage occurs

Question 28

Describe the importance of mitosis.

Answer 28

- genetic stability - Growth - Cell replacement, for example, in the skin where are cells die - Regeneration, for example, in the arms of starfish - Asexual reproduction

Question 29

Describe the importance of meiosis

Answer 29

- sexual reproduction, since haploid gametes are produced - Genetic variation which leads to evolution

Question 30

State the differences between mitosis in plant and animal cells

Answer 30

ANIMALS - centrioles present - Asters form - Furrowing occurs - Occurs in somatic cells PLANTS - centrioles absent - No asters form - Furrowing does not occur - Occurs mainly in meristems

Question 31

What are the similarities of mitosis in plants and animals?

Answer 31

- in both two daughter cells are formed - In both mitosis shows similar stages - In both daughter cells formed are identical

Question 32

What are the differences between mitosis and meiosis?

Answer 32

MITOSIS - results information of two daughter cells - Occurs in somatic cells - No crossing over occurs - Occurs in haploid diploid and polyploid cells - Homologous chromosomes remain separate - No, chiasmata formed - The same number of chromosomes present in daughter cells as parent cells MEIOSIS - results information of four daughter cells - Occurs in gametes - Crossing over may occur - Occurs in diploid or polyploid cells - Homologous chromosomes may pair up - Chiasmata may be formed - Half the number of chromosomes present in daughter cells as parent cells

Question 33

Give the similarities between mitosis and meiosis

Answer 33

- both involve four stages of cell division - Both are preceded by interphase - Both are energy consuming processes - Both involve nuclear division and cytokinesis

Question 34

Give differences between DNA and RNA

Answer 34

DNA - Double stranded - Deoxyribose - Contains thymine - Chemically stable -Permanent (long lived) - Self-replicating - Linear or circular RNA - Single stranded - Ribose sugar - Contains uracil - Chemically less stable -Temporary(short lived) - Synthesized from DNA when needed - Structure varies with each type of RNA

Question 35

What are the similarities of DNA and RNA?

Answer 35

- Both are polymers of nucleotides - Both carry genetic information - Both originate from the nucleus

Question 36

Why is it that a purine only bonds to a pyrimidine?

Answer 36

- Purine + purine = insufficient room for them to fit - Pyrimidine + pyrimidine = too much unoccupied space

Question 37

Give properties of the genetic code

Answer 37

Punctuated; - It has start at stop codons - AUG is always the start point and the stop is UAA, UAG or AGA (nonsense codons) Universal; -All living organisms have the same 20 common amino acids and same five bases (A, U, C, G, T) Non-overlapping; - Read in triplets and the last base in a codon cannot be the first of the next Degenerate; - A given amino acid may be coded for by more than one codon The code is triplet - A triplet of bases in the polynucleotide chain is the code of one amino acid in the polypeptide chain

Question 38

What is a codon?

Answer 38

A triplet of bases of mRNA that codes for a particular amino acid

Question 39

Give causes of cancer

Answer 39

-Chemicals - Radiations - Viruses

Question 40

What are the means of preventing cancer?

Answer 40

- Avoid exposure to radiation - Avoid smoking - Vaccination - Regular check ups - Sensitization

Question 41

What are the treatments for cancer?

Answer 41

- Chemotherapy - Surgery - Radiotherapy - Use of lasers - Use of radio waves

Question 42

Define cancer

Answer 42

Uncontrolled cell growth

Question 43

What is a tumor?

Answer 43

Irregular mass of undifferentiated cells

Question 44

What is a malignant tumor?

Answer 44

Tumor that can invade other tissues or organs

Question 45

What is a benign tumor?

Answer 45

These occur at one site and do not spread

Question 46

What is the genetic significance of DNA replication?

Answer 46

- Allows inheritance of genetic material by offspring in constant amounts - Ensures that genetic material is constant within organisms of a given species - Directs synthesis of many proteins from few DNA molecules

Question 47

Give ways that suggest that DNA is a hereditary material

Answer 47

- DNA is associated with hereditary structures such as chromosomes - Amount of DNA is the same in somatic cells of organisms of the same species - DNA is chemically stable