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DNA Replication. Vocabulary: Replication - Synthesis of an identical copy of a DNA strand. http://www.lewport.wnyric.org/jwanamaker/animations/DNA%20Lecture.html. In which cell organelle is DNA replicated?. Nucleus. When does DNA cell replication occur?. Before a cell divides

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dna replication

DNA Replication


Replication - Synthesis of an identical copy of a DNA strand.


in which cell organelle is dna replicated
In which cell organelle is DNA replicated?
  • Nucleus

When does DNA cell replication occur?

  • Before a cell divides
  • Mitosis & Meiosis

When DNA replicates, it results in __________ of the number of chromosomes in a cell?




Is the blueprint of life (has the instructions for making an organism) established by James Watson and Francis Crick

-codes for your genes

-shape of a double helix

-made of repeating subunits called nucleotides

Nucleotide - consists of a sugar, phosphate and a base

Nitrogenous Bases

Adenine, Thymine, , Guanine, Cytosine or A, T, G, C

Nucleotides pair in a specific way

- called the Base-Pair Rule

Adenine pairs to Thymine

Guainine pairs to Cytosine

To make a copy of any thing, you need an original or template.
  • DNA has the template build in.
  • Replication begins when the double helix unzipping.
  • A enzyme breaks the __________ bonds in the DNA exposing the template.

If you know the sequence of base on one strand, you can predict the sequence on the other strand. (Base ? ___________)


What is the sequence of nitrogen bases on the left side of the DNA molecule below?


Predict the sequence of nitrogen bases on the right side of the DNA molecule below?




If one strand of DNA has the base sequence C A T G A G C G C G A T , what will be the sequence on the other strand? > GTA CTC GCG CTA

How DNA replicates

Understanding this goes a long way to explaining how nuclei divide in the process of mitosis , which results in identical copies of chromosomes being transferred during ordinary cell division.Before a cell divides, its nucleus must divide. But before that happens, the chromosomes must have become double. So the first stage is that DNA which the chromosomes contain must replicate , i.e. become double, by making copies of itself.The 2 strands of the DNA double helix can separate, under the influence of special enzymes in the nucleus, but each half remains attached along its length, like the 2 sections of a zip, because the sides of the strands are strongly joined.In the diagrams below, write in the letters for the various bases (using the first few as a key). This should help you understand the results of the process.

DNA replication

Each strand then acts as a basis for rebuilding the missing other strand from which it has been separated. It is said that each strand forms a template on which it reforms its complementary strand. Enzymes within the nucleus match the appropriate base, which is already attached to strand side subunits, so that A fits against T, G against C, T against A and C against G, according to shape.Other possibilities are not allowed, so the copying process is accurate in the vast majority of cases.The result is that one double strand is converted into two identical double strands.It is interesting to note that each "new" double strand is in fact half composed of a section of the previous DNA molecule, together with a completely new section built up from individual bases.

Because of this, it is called semi-conservative replication.


HW Read Page 413-416 and answer pg 416

#7,12, 13,14 15 Q&A on LL

what are genes
What are Genes?

Genes are areas on the DNA molecule that code for the synthesis of specific proteins.

What is The Genetic Code?

It is three adjacent nucleotides (“letters”) in mRNA that specify an amino acid in a polypeptide, (_________) molecule.

  • Proteins determine the traits in organisms so
  • therefore, genes determine the specific traits of
  • an organism.
protein synthesis

Protein Synthesis

Is a process whereby DNA encodes for the production of amino acids and proteins.

This process can be divided into two parts:1. Transcription 2. Translation


Transcription - Synthesis of mRNA

Translation - Synthesis of polypeptide from amino acids.

Codon - Base triplet on mRNA.

Anticodon - Complementary triplet on tRNA.

Polypeptide - ______ molecule

DNA is too large to leave the Nucleus, so

how does the information (genetic codes) within the DNA molecule get to the ribosome’s where proteins are synthesized?

An intermediate molecule is needed.



RNA is that molecule.It is single stranded and thus is smaller than DNA & able to leave the nucleus through the nuclear pores and carry the codes to the ribosome

Uracil (U)* instead of Thymine (T)





Uracil (U)* instead of Thymine (T) in the RNA

protein synthesis14

Two parts:

1. Transcription 2. Translation

step 1 of protein synthesis transcription
Step 1 of Protein SynthesisTRANSCRIPTION

One strand of the DNA double helix is used as a template by the RNA polymerase to synthesize a messenger RNA (mRNA).

The mRNA then migrates from the nucleus to the ribosome.


The DNA molecule unzips /opens up on one side only and the base sequence is transcribed into a complementary sequence of bases forming a mRNA molecule. Remember Uracil (U)* instead of Thymine (T)

What will the sequence of bases in the mRNA?

DNA Sequence (left side) __A C A____G G A______C G A______

mRNA Sequence _________________________________________

what is a codon
What is a Codon?
  • A sequence of three nucleotides that encode for an amino acid or signifies a start or stop signal.
  • NOTE*

AUG = Start & Methionine Amino Acid

UAA = Stop

codons cont
Codons cont
  • There are 64 possible codons corresponding to 20 amino acids.
  • NOTE * The Start codon corresponds to the amino acid methionine and the stop codon have no amino acids attached.
step 2 of protein synthesis translation
Step 2 of Protein SynthesisTranslation

- What is it?

The coded information flows from the DNA to the ribosome via the mRNA and then tRNA brings the corresponding amino acid.

Where does it take place?


2 translation
2. Translation

Steps in Translation

  • Initiation
  • Elongation
  • Termination



Step 1. Initiation______

(1) Initiation The ribosome binds to the mRNA at the start codon (_____) that is recognized only by the initiator tRNA.

step 2 elongation
Step 2. Elongation
  • whereby the correct amino acid is brought to the ribosome and a peptide bond forms between adjacent amino acids and the entire assembly moves one position along the mRNA.
  • The polypeptide chain continues to grow..
step 3 termination
Step 3. Termination
  • Termination which happens when a stop codon is reached, there is no amino acid to be incorporated and the entire assembly dissociates to release the newly-synthesized polypeptide.
  • What are the stop codons?


  • Information flows from DNARNAProteins
  • RNA serves as the intermediary between DNA and proteins.
  • There are three types of RNA. mRNA, rRNA and tRNA.
  • The Genetic Code represents 64 possible codons corresponding to 20 different amino acids, start signal and stop signals.
  • The process of TRANSLATION takes place within the cytoplasm on a ribosome.
  • The process of TRANSLATION involves: initiation, elongation and termination.
in what cell organelle are proteins synthesized
In what cell organelle are proteins synthesized ?
  • Ribosome's

Which cell organelle controls the manufacture of proteins in the ribosome?

  • Nucleus

What is in the nucleus contains the information for protein synthesis

  • DNA


There are twenty amino acids required for human life to exist. Adults have eight essential amino acids that they cannot synthesize. The other twelve can be produced within our bodies.

Essential amino acidshistidine, isoleucine, leucine, lysine,

methionine, phenylalanine, threonine, tryptophan, and valine.

what in the nucleus controls cell activities
What in the nucleus controls cell activities?

What in the nucleus contains the codes for protein synthesis?

  • The information within the DNA molecule is encoded within the sequence of the nitrogenous bases.

Answer: The DNA