Nucleic Acids, Protein Synthesis & Cell Division Flashcards
True or false;
Nucleic acids are organic
True
Describe the structure of nucleotides
- 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
Describe the process of formation of a nucleotide
- 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
Describe the structure of DNA according to Watson & Crick
- 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
Describe the semi conservative theory
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)
Describe the process of DNA replication
- 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
Give the similarities between the lagging strand and the leading strand
- both are templates for DNA replication
- Both form half of the new DNA
Give the differences between the leading strand in the lagging strand
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
What are the adaptations of DNA to its functions?
- 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
Why is DNA confined to the nucleus?
- to prevent alteration by chemical reactions in the cytoplasm
- It is too large to fit through the nuclear pores
What is the use of ribosomes in proteins synthesis?
They are a point of anchorage for the tRNA and mRNA molecules
What is transcription?
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
Where does transcription occur?
It occurs in the nucleus
Where does translation occur ?
Cytoplasm, Ribosome
What is translation?
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
What is the importance of transcription?
- DNA is too large to fit through the nuclear pores yet mRNA being small can readily exit the nucleus
- DNA contains many codes that aren’t always needed at a given time so mRNA only carries the code needed to make specific proteins
Describe the process of transcription
[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
Describe the process of translation
- Binding of mRNA to ribosome
- Amino acid, activation, and attachment to tRNA
- Polypeptide, chain initiation
- Chain elongation
- Chain termination
- Fate of the polypeptide chain
Define cell cycle
The cell cycle is the sequence of events which occurs between one cell division, and the next.
State the constituents of interphase in cells
- G1 phase
- Synthesis phase
- G2 phase
Describe growth phase 1 of the cell
- intense cellular synthesis of new cell organelles
- Highly metabolically, active
- Rapid cell growth
- Overall cell mass increases
Describe the synthesis phase of the cell
- DNA replication (only in eukaryotes)
- Synthesis of histones
- Each chromosome exist as two chromatids
Describe growth, phase 2 of the cell
- intense cellular synthesis
- Centrioles replicate
- Mitochondria and chloroplasts divide
- Energy stores increase
- Overall cell size increases
- Mitotic spindle begins to form
What is meant by the term mitosis ?
This is the formation of two identical daughter cells, which are diploid like the parent cell.
Describe the events that take place during mitosis in animal cells
- 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 - 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 - Anaphase
- centromere split into two and spindle fibers pull daughter centromeres to opposite poles
- Separated, chromatids are pulled along behind the centromeres - 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 - 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
Define meiosis
This is a form of nuclear division in which the chromosome number is halved from the diploid number to the haploid number
Describe the process of meiosis
- 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 - Metaphase one
- The by valance are arranged at the equator of the spindle attached by the centromeres
- They are randomly assorted along the equator - 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 - 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 - 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 - Metaphase two
- chromosomes line up separately around the equator of the spindle - Anaphase two
- centromeres divide
- spindle fibers pull the chromatids to opposite poles by the centromeres - Telophase two
- four haploid daughter cells are formed
- Chromosomes uncoil, lengthen, and become indistinct
- Spindle fibers disappear
- Centrioles replicate
- Nuclear envelope reform
- Cleavage occurs
Describe the importance of mitosis.
- genetic stability
- Growth
- Cell replacement, for example, in the skin where are cells die
- Regeneration, for example, in the arms of starfish
- Asexual reproduction
Describe the importance of meiosis
- sexual reproduction, since haploid gametes are produced
- Genetic variation which leads to evolution
State the differences between mitosis in plant and animal cells
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
What are the similarities of mitosis in plants and animals?
- in both two daughter cells are formed
- In both mitosis shows similar stages
- In both daughter cells formed are identical
What are the differences between mitosis and meiosis?
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
Give the similarities between mitosis and meiosis
- both involve four stages of cell division
- Both are preceded by interphase
- Both are energy consuming processes
- Both involve nuclear division and cytokinesis
Give differences between DNA and RNA
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
What are the similarities of DNA and RNA?
- Both are polymers of nucleotides
- Both carry genetic information
- Both originate from the nucleus
Why is it that a purine only bonds to a pyrimidine?
- Purine + purine = insufficient room for them to fit
- Pyrimidine + pyrimidine = too much unoccupied space
Give properties of the genetic code
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
What is a codon?
A triplet of bases of mRNA that codes for a particular amino acid
Give causes of cancer
-Chemicals
- Radiations
- Viruses
What are the means of preventing cancer?
- Avoid exposure to radiation
- Avoid smoking
- Vaccination
- Regular check ups
- Sensitization
What are the treatments for cancer?
- Chemotherapy
- Surgery
- Radiotherapy
- Use of lasers
- Use of radio waves
Define cancer
Uncontrolled cell growth
What is a tumor?
Irregular mass of undifferentiated cells
What is a malignant tumor?
Tumor that can invade other tissues or organs
What is a benign tumor?
These occur at one site and do not spread
What is the genetic significance of DNA replication?
- 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
Give ways that suggest that DNA is a hereditary material
- 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
