Chapter 11 Biology DNA and Genetics
In DNA, there are four possible nitrogenous bases:
adenine (A), guanine (G), cytosine (C), and thymine (T)
ribosomal RNA (rRNA)
binds to the mRNA and uses the instructions to assemble the amino acids in the correct order
transcription
enzymes make an RNA copy of a portion of a DNA strand
Single-ringed nitrogenous bases, thymine and cytosine are called _____.
pyrimidines
Differences between RNA and DNA:
1) An RNA molecule usually consists of a single strand of nucleotides, not a double strand. This single-stranded structure is closely related to its function. 2) Ribose is the sugar in RNA, rather than the deoxyribose sugar in DNA. 3) The nitrogenous base uracil (U) replaces thymine (T) in RNA. In RNA, uracil forms base pairs with adenine just a thymine does in DNA.
Process of translation:
1) As translation begins, a ribosome attaches to the mRNA strand. Molecules of tRNA, each carrying a specific amino acid, approach the ribosome. 2) The codon AUG, which codes for the amino acid methionine, signals the start of protein synthesis. The tRNA molecule carrying methionine attaches to the ribosome and mRNA strand. 3) A new tRNA molecule carrying an amino acid attaches to the ribosome and mRNA strand next to the previous tRNA molecule. The amino acids on the tRNA molecules join by peptide bonds. 4) After the peptide bond is formed, the ribosome slides along the mRNA to the next codon. The tRNA molecule no longer carrying an amino acid is released. A new tRNA molecule carrying an amino acid can attach to the ribosome and mRNA strand. 5) A chain of amino acids is formed until a stop codon is reached on the mRNA strand.
Structure of DNA:
1) In each chain of nucleotides, the sugar of one nucleotide is joined to the phosphate group of the next nucleotide by a covalent bond. 2) The two chains of nucleotides in a DNA molecule are held together by hydrogen bonds between the bases. In DNA, cytosine forms three hydrogen bonds with guanine, and thymine forms two hydrogen bonds with adenine. 3) Complementary base pairing produces a long, two-stranded molecule that is often compared to a zipper. As you can see, the sides of the zipper are formed by the sugar and phosphate units, while the teeth of the zipper are the pairs of bases.
Process of transcription:
1) The process of transcription begins as enzymes unzip the molecule of DNA in the region of the gene to be transcribed. 2) Free RNA nucleotides form base pairs with their complementary nucleotides on the DNA strand. The mRNA strand is complete when the RNA nucleotides bond together. 3) The mRNA strand breaks away, and the DNA strands rejoin. The mRNA strand leaves the nucleus and enters the cytoplasm.
Copying DNA:
1) When a cell begins to copy its DNA, the two nucleotide strands of a DNA molecule separate when the hydrogen bonds connecting the base pairs are broken. As the DNA molecule unzips, the bases are exposed. 2) The bases in free nucleotides pair with exposed bases in the DNA strand. If one nucleotide on a strand has thymine as a base, the free nucleotide that pairs with it would be adenine. If the strand contains cytosine, free guanine nucleotide will pair with it. Thus, each strand builds its complement by base pairing-forming hydrogen bonds-with free nucleotides. 3)The sugar and phosphate parts of adjacent nucelotides bond together with covalent bonds to form the backbone of the new strand. Each original strand is now hydrogen-bonded to a new strand. 4) The process if replication produces two molecules of DNA. Each new molecule has one strand from the original molecule and one strand that has been newly synthesized from free nucleotides in the cell.
Role of transfer RNA:
A tRNA molecule is composed of about 80 nucleotides. Each tRNA recognizes only one amino acid. The amino acid becomes bonded to one side of the tRNA molecule. Located on the other side of the tRNA molecule are three nitrogenous bases, called an anticodon, that pair up with an mRNA codon during translation.
nitrogenous base
a carbon ring structure that contains one or more atoms of nitrogen
point mutation
a change in a single base pair in DNA
frameshift mutation
a mutation in which a single base is added to or deleted from DNA
Nucleotides have three parts:
a simple sugar, a phosphate group, and a nitrogenous base
mutagen
any agent that can cause a change in DNA
mutation
any change in the DNA sequence
messenger RNA (mRNA)
brings instructions from DNA in the nucleus to the cell's factory floor, the cytoplasm
transfer RNA (tRNA)
delivers amino acids to the ribosome to be assembled into a protein
Because DNA is composed of two strands twisted together, its shape is called a ______.
double helix
codon
each group of three nitrogenous bases in mRNA code for one amino acid
Regions that contain information are called ______ because they are expressed.
exons
When something is twisted like a spring, the shape is called a _____.
helix
Genes usually contain many long noncoding nucleotide sequences, called _______, that are scattered among the coding sequences.
introns
The simple sugar in DNA, called deoxyribose, gives DNA what?
its name-deoxyribonucleic acid
The phosphate group is composed of what?
one atom of phosphorus surrounded by four oxygen atoms
DNA
polymer made of repeating subunits called nucleotides
translation
process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein
Double-ringed nitrogenous bases, adenine and guanine are called ______.
purines
nucleotide
subunit of a nucleic acid formed from a simple sugar, a phosphate group, and a nitrogenous base
DNA replication
the DNA in the chromosomes is copied
chromosomal mutations
the structural changes in chromosomes
deletion
when a part of a chromosome is left out
insertion
when part of a chromatid breaks off and attaches to its sister chromatid, resulting in a duplication of genes on the same chromosome
inversion
when part of a chromosome breaks off and reattaches backwards
translocation
when part of one chromosome breaks off and is added to a different chromosome