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Biology Notes

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Biology Notes Essay, Research Paper

DNA is a very large polymer made up of many monomers called nucleotides

Each Dna nucleotide consist of:

a. the sugar deoxyribose

b. a nitrogen base

The only difference between the four types of Dna is there nitrogen bases.

The four nitrogen bases of DNA are the organic ring structures

a. adenine

b. thymine

c. guanine

d. cytosine

One way to determine the structure of a substance is by X-ray diffraction.

X-ray diffraction—-a beam is passed through a pure crystal of the substance.

Rosalind Franklin carried out x-ray diffraction on very pure fibers of DNA.

The patterns on her x-ray film showed that the phosphate of one nucleotide was linked

to the sugar of the next, forming a continuos chain.

The phosphate-sugar chain forms a backbone for each strand. The nitrogen bases of

each strand pair with the nitrogen bases of the other strand by hydrogen bonding.

The nitrogen base Adenine (A), only bonds with Thymine (T), and the base Guanine

(G), only bonds with Cytosine (C).

Because there are two strands in a spiral, the shape of DNA is described as a double


The DNA double helix is compared to a twisted ladder. The sides of the ladder are the

sugar-phosphate backbones and the rungs are the pairs of nitrogen bases.

Replication—- The process by which a DNA molecule is copied.

The four nitrogen base ?A?, ?C?, ?G?, and ?T? make up the genetic alphabet.

Each strand then serves as a pattern along which a new strand can form.

When a DNA molecule replicates enzymes ?unzip? the two strands along the paired


Codon—–as sequence of three bases.

a codon is a unit of the genetic code.

different codons specify different amino acids.

There are 64 different combinations possible with the four different nitrogen bases

taken three at a time.

There are only 20 amino acids. Therefore, three or four codons may stand for the

same amino acid.

One codon is a start codon that begins the production of a protein chain.

Three different codons are stop codons which end the protein chain.

The genetic code is copied for use at the site of protein synthesis, the ribosome.

Like DNA, RNA is a nucleic acid made of bonded nucleotides.

DNA contains the sugar deoxyribose but RNA contains ribose a different sugar.

Instead of the base Thymine RNA contains the base Uracil (U)

Uracil bonds with the adenine just like thymine.

There are three kinds of RNA:

a. messenger RNA (mRNA)

b. transfer RNA (tRNA)

c. ribosomal RNA (rRNA)

mRNA is the RNA copy of the DNA code for the sequence of amino acids in a

particular protein chain

mRNA transfers the genetic code from the DNA in the nucleus to the ribosome?s in

the cytoplasm.

tRNA transfers amino acids to the ribosome for addition to the protein chain.

rRNA makes up a part of the ribosome.

Transcription—–the construction of RNA along portions of the DNA molecule. All

three types of RNA are made from transcription from DNA.

Each tRNA also has a triplet of nitrogen bases called an anticodon.

Prokaryotes reproduce by a process called binary fission.

Each DNA molecule with its associated proteins is called a chromosome. Human cells

for instance have 46 chromosomes

Mitosis——is the division of the nucleus into two nuclei containing identical DNA

Chapter 8

Chromosomes Rae threadlike structures inside the nucleus.

A chromosome is made up of genes

A Gene—– is a segment of DNA that helps to control a particular hereditary trait

such as leaf length or eye color.

Each chromosome of a set matches one from the other set. In other words, the

chromosomes occur in pairs. The members of each chromosome pair are called

homologous chromosomes.

A cell that contans two sets of chromosomes is called a diploid.

When an organism reproduces sexually, the number of chromosomes found in a body

cell is halved during the production of gametes.

Gamete—-is a sex cell.

The female gamete is an egg.

The male gamete is a sperm.

A haploid or monoploid cell is one that contains one set of chromosomes.

Meiosis—- the process of cell division that results in the formation of gametes.

Meiosis occurs in the cells of reproductive organs.

The first division is ofte known as the reduction division, because the chromosome

number is reduced by half to the monoploid condition.

In the second division the sister chromatids of each separate when their centromeres

break apart.

In Prophase 1 of meiosis:

a. chromosomes shorten

b. they coil and contract

c. nuclear membrane dissolves and disappears.

d. the chromatids of each pair of homologous chromosomes wind around each


e. pieces of chromosomes from pairs of sister chromatids are exchanged.

This exchange of genetic material is called crossing over.

Genotype——a organisms genetic makeup

Fertilization—-the fusion of a male and female gamete.

Phenotype——an organisms outward appearance

Sex chromosomes carry genes that determine the sex of an individual

Genes that are usually inherited together are called linkage groups.

Humans have 23 linkage groups

Genetic Recombination——when two homologous chromosomes ?mix and match?


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