Key Facts
Cell The smallest unit of life
Nucleus Organelle that contains genetic information (DNA) as chromosomes within eukaryotic cells
Chromosome Long, independent lengths of DNA found in the nucleus
Gene A section of a molecule of DNA that codes for a specific protein
DNA Molecule with a code on it that codes for a sequence of amino acids (proteins) and therefore
characteristics (this is it’s purpose)
Genome The entire DNA of an organism
DNA Structure
A nucleotide is made up of a nitrogenous base (either adenine, A, thymine, T, cytosine, C, or guanine, G), a
phosphate group and a deoxyribose sugar.
The nucleotides link via a bond between the phosphate group of one nucleotide and the deoxyribose sugar of
another to make the long strand.
Two strands line up in an antiparallel way.
The bases of one strand will join via hydrogen bonds with the bases
of the
antiparallel strand in a complementary way. Adenine joins with
thymine via 2
hydrogen bonds and cytosine joins with guanine via 3 hydrogen
bonds.
The two strands coil into a double helix shape.
RNA, Codons and Anticodons
RNA is a single stranded molecule of genetic information. It has the base uracil instead of thymine. There are 2 types
that you need to know:
1. Messenger RNA (mRNA) 2. Transfer RNA (tRNA)
A codon is a base triplet found on DNA or mRNA that codes for one amino acid. An anticodon is a base triplet found
on tRNA that is complementary to a codon.
Because there are 4 types of base, there are 64 possible types of codon (4 x 4 x 4). There are only 20 types of amino
acids, so some codons code for the same amino acid.
, Protein Synthesis
1) Transcription
This happens in the nucleus
RNA polymerase binds to a region of non-coding DNA in front of the gene to be transcribed
The two strands of DNA unzip and the RNA polymerase moves along the coding DNA
As the RNA polymerase moves along, it joins together RNA molecules that are complementary to the base sequence
of the coding DNA (U beside A, A beside T, G beside C and C beside G)
The molecule of mRNA passes out of the nucleus into to cytoplasm via a nuclear pore
2) Translation
This happens in the cytoplasm
The mRNA attaches to a ribosome
Amino acids are brought to the mRNA by tRNA (one specific amino acid per tRNA determined by the anticodon)
The anticodon will match up to a complementary codon on the mRNA (U complementary to A and C complementary
to G)
Many amino acids are brought towards the mRNA by the tRNA in this way, so that they line up in specific order
The ribosome joins the amino acids together (forms peptide bonds)
The tRNA detaches to be reused again
Sex Determination
The sex chromosomes form the 23rd pair when all the chromosomes of a cell are lined up in their pairs. The sex
chromosome is either an X or a Y chromosome and each person inherits one from each parent. Females have
genotype XX and males XY.
The male determines the sex of a baby, because he will produce sperm that are either X or Y. There is a 50% chance
that the sperm will be X, resulting in a girl and 50% chance that the sperm will be a Y, resulting in a boy. The female
can only produce eggs that are X.
The fact that there is a 50/50 chance of having a girl or boy can be shown in a genetic diagram known as a punnet
square.
Punnet squares are
good to draw as part Female
of an answer, but you gametes
must label it (male /
female gametes,
genotypes, Potential genotypes = XX or XY (1:1)
phenotypes and Male Potential phenotypes = girl or boy
ratios) or you won’t gametes (1:1)
get full credit.
Cell The smallest unit of life
Nucleus Organelle that contains genetic information (DNA) as chromosomes within eukaryotic cells
Chromosome Long, independent lengths of DNA found in the nucleus
Gene A section of a molecule of DNA that codes for a specific protein
DNA Molecule with a code on it that codes for a sequence of amino acids (proteins) and therefore
characteristics (this is it’s purpose)
Genome The entire DNA of an organism
DNA Structure
A nucleotide is made up of a nitrogenous base (either adenine, A, thymine, T, cytosine, C, or guanine, G), a
phosphate group and a deoxyribose sugar.
The nucleotides link via a bond between the phosphate group of one nucleotide and the deoxyribose sugar of
another to make the long strand.
Two strands line up in an antiparallel way.
The bases of one strand will join via hydrogen bonds with the bases
of the
antiparallel strand in a complementary way. Adenine joins with
thymine via 2
hydrogen bonds and cytosine joins with guanine via 3 hydrogen
bonds.
The two strands coil into a double helix shape.
RNA, Codons and Anticodons
RNA is a single stranded molecule of genetic information. It has the base uracil instead of thymine. There are 2 types
that you need to know:
1. Messenger RNA (mRNA) 2. Transfer RNA (tRNA)
A codon is a base triplet found on DNA or mRNA that codes for one amino acid. An anticodon is a base triplet found
on tRNA that is complementary to a codon.
Because there are 4 types of base, there are 64 possible types of codon (4 x 4 x 4). There are only 20 types of amino
acids, so some codons code for the same amino acid.
, Protein Synthesis
1) Transcription
This happens in the nucleus
RNA polymerase binds to a region of non-coding DNA in front of the gene to be transcribed
The two strands of DNA unzip and the RNA polymerase moves along the coding DNA
As the RNA polymerase moves along, it joins together RNA molecules that are complementary to the base sequence
of the coding DNA (U beside A, A beside T, G beside C and C beside G)
The molecule of mRNA passes out of the nucleus into to cytoplasm via a nuclear pore
2) Translation
This happens in the cytoplasm
The mRNA attaches to a ribosome
Amino acids are brought to the mRNA by tRNA (one specific amino acid per tRNA determined by the anticodon)
The anticodon will match up to a complementary codon on the mRNA (U complementary to A and C complementary
to G)
Many amino acids are brought towards the mRNA by the tRNA in this way, so that they line up in specific order
The ribosome joins the amino acids together (forms peptide bonds)
The tRNA detaches to be reused again
Sex Determination
The sex chromosomes form the 23rd pair when all the chromosomes of a cell are lined up in their pairs. The sex
chromosome is either an X or a Y chromosome and each person inherits one from each parent. Females have
genotype XX and males XY.
The male determines the sex of a baby, because he will produce sperm that are either X or Y. There is a 50% chance
that the sperm will be X, resulting in a girl and 50% chance that the sperm will be a Y, resulting in a boy. The female
can only produce eggs that are X.
The fact that there is a 50/50 chance of having a girl or boy can be shown in a genetic diagram known as a punnet
square.
Punnet squares are
good to draw as part Female
of an answer, but you gametes
must label it (male /
female gametes,
genotypes, Potential genotypes = XX or XY (1:1)
phenotypes and Male Potential phenotypes = girl or boy
ratios) or you won’t gametes (1:1)
get full credit.
