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 Cell Tissue Gene DNA Mitosis Meiosis |
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Cell Tissue Gene DNA Mitosis Meiosis |
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 Kolej Matrikulasi Perak. This is only an assignment-purpose blog! Contact Me
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  10:19 | 0 Cloud(s) DNA Replication
DNA Replication :
*It is a semi-conservative process
*The daughter DNA molecules produced consist of one progeny and one parental strand
DNA as Template
*Each strand of the parent DNA acts as template, make the new daughter strand
*Makes 2 new complete double helices
*Each with 1 old and 1 new strand
*DNA synthesis proceeds only in the 5' 3'direction which means that the strand being copied is been read in the 3' 5' direction
*DNA replication begins at specific base sequence (Origin of replication) when helicase binds to parental
*DNA and begins to unwind it (break the H bond)
*Each parent strand becomes a template used to synthesize the complimentary strand
*Single-strand binding (SSB) protein bind to single DNA strands and stabilize them
*Prevents the double helix from re-forming until the strand are replicated
*Both strand require RNA primer for initiation of synthesis because DNA can be elongated only by addition to 3' end of existing polynucleotide strand
Leading Strand (template 3’ – 5’)
*RNA primase synthesize the primer:
- 5-14 nucleotides
- To provide the 3’ OH end
*DNA polymerase binds to the 3’ end
- Add nucleotides to the growing end
*The primer will be digested by DNA polymerase
- Replaced by DNA
*Primer will be joined by DNA ligase
*DNA polymerase binds to the 3’ end
- Add nucleotides to the growing end
Lagging Strand (template 5’ – 3’)
*RNA primase synthesize the primer
*DNA polymerase binds to the 3’ end
- Add nucleotides to the growing end
*Moves discontinuously away from the replication fork
*Forms short fragments - Okazaki fragments
*The primer will bedigested by DNA polymerase
- Replaced by DNA
*All Okazaki fragments are joined by DNA ligase
*New complementary DNA strand 3’ - 5’
Animation : DNA Replication Process
10:18 | 0 Cloud(s)Transcription
Transcription :
*Process where the information in DNA is transcribed to a RNA molecule (mRNA)
*Occur in the nucleus
*Single strand of DNA act as as a template
*Only part of DNA will be copied
*Direction : 5’ 3’
*Catalaysed by RNA polymerase
Initiation
*RNA polymerase binds to DNA at a specific sequence of nucleotides called the promoter
*The promoter contains an initiation site where transcription of the gene begins
*RNA polymerase than unwinds DNA at thebeginning of the gene
Elongation
*Only one of the unwound DNA strands acts as a template for the RNA synthesis
*RNA polymerase can only add nucleotids to the 3' end of the strand so like DNA, RNA must be synthesized in the 5' to 3' direction
*Free ribonucleotides from the cytoplasm are paired up with their complementary base on the exposed DNA template
*RNA polymerase joins the ribonucletides to form mRNA strand
*The DNA that has been transcribed, re-winds to form a double helix
Termination
*RNA polymerase continues to elongate until it reaches the terminator, a specific sequence of nucleotides that signals the end of transcription
*Transcription stops and mRNA polymerase and the new mRNA transcript are released from DNA. DNA double helix reforms
Animation : Transcription Process
10:17 | 0 Cloud(s)Lac Operon
Operon and Gene Regulation :
*Operon are multiple genes that part of a single gene expression unit
*Lac operon : the protein necessary for the utilization of lactose
Absence of Lactose
*Repressor protein bind to the operator site
*Blocking the promoter site
*Prevent RNA polymerase from binding to the promoter site
*Prevent transcribing the structural genes.
*The structural genes that code for the enzyme needed to digest lactose are not transcribed
*No production of lactose digested enzymes
Persence of Lactose
*Lactose convert to allolactose and bind to the repressor
*Changing repressor shape so that it is inactive and cannot bind to the operator
*RNA polymerase bind to promoter
*The structural genes are transcribed into mRNA that later translated into enzymes that digest lactose
Animation : Lac Operon Process
10:14 | 0 Cloud(s)Translation
Translation :
*The synthesis of proteins
directed by a mRNA template
*Take place on ribosomes
in the cytoplasm
Initiation
*The small subunit of a ribosome, bind to the 5’ end of an mRNA molecule
*AUG codon (start codon) indicates initiation of translation
*Initiation occurs when first tRNA carrying Methionine (UAC anticodon) binds to AUG codon on mRNA
*First tRNA occupies the P site whereas A site is ready for the next tRNA
Elongation
Elongation consists of three steps:
1) positioning the next amino acid;
2) peptide bond formation;
3) moving the ribosome to the next codon.
*Once both sites are filled by tRNA’s, along with their corresponding amino acids, the ribosome links the two amino acids together forming a peptide bond
Termination
*The ribosome reaches one of three stop codons (UAA, UAG, UGA)
*At this point a special protein termed a release factor binds to the mRNA instead of a tRNA bearing an amino acid
*An enzyme subsequently serves to separate the polypeptide chain from the last tRNA
*At this point, both large and small ribosomal subunits dissociate from one another and become available to repeat the process
Animation : Translation Process
10:06 | 0 Cloud(s)Active Transport
Active Transport :
*The
movement of a substance across a cell membrane against its concentration, mediated by specific transport proteins and
require an expenditure of energy.
*Location
: Nerve Cell , Nephrons & e.t.c
*Example : Sodium-Potassium Pump
Sodium-Potassium
Pump
*Cells
usually have more sodium ions outside and more potassium ions
inside.
*Transport
3 sodium ions (Na+) out of the cell & 2 potassium ions (K+) into the cell.
*Involved
Phosphorylation
:
- Addition of a phosphate group to a protein or organic molecules - Phosphorylation causes the protein to change its conformation.      
Animation : Sodium-Potassium Pump
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