Biology - 13 Reproduction - 13.4 DNA and the Genome & 13.5 DNA Structure and Protein Synthesis & 13.6 Gene Expression and Mutation

Order smallest to largest:
- DNA
- nucleotides
- genes
- chromosomes
- bases

- bases
- nucleotides
- genes
- DNA
- chromosomes

Nucleobases of DNA [4]:

- adenine (A)
- thymine (T)
- guanine (G)
- cytosine (C)

Complementary base pairing [2]:

- A to T
- C to G

Nucleotide

monomer of DNA

Components of nucleotides [3]:

- phosphate
- pentose sugar
- nucleobase

Pentose sugar in DNA:

deoxyribose sugar

Pentose sugar in RNA:

ribose sugar

Gene

segment of DNA that codes for a protein and thus determines a trait

Genetic code

ordering of nucleotides in DNA molecules that carries the genetic information in living cells

Codon

three-nucleotide sequence on DNA or mRNA that codes for a single amino acid

Anticodon

three-nucleotide sequence on tRNA that is complementary to codons in mRNA

Protein

organic polymer made of monomers of amino acids

Genome

all the genetic material in an organism, including that in the chromosomes and the mitochondria

How are proteins made from DNA? (simplified) [5]

- a template is produced from the DNA in the nucleus
- the template leaves through pores in the nuclear membrane
- the template attaches to a ribosome
- carrier molecules in the cytoplasm attach amino acids as instructed by the template
- the protein detaches and folds into a specific shape

RNA

ribonucleic acid

RNA structure:

single-stranded

Nucleobases of RNA [4]:

- adenine (A)
- uracil (U)
- guanine (G)
- cytosine (C)

Where in the cell is RNA found?

cytoplasm and nucleus

Where in the cell is DNA found?

nucleus

RNA polymerase

enzyme that links together the chain of RNA nucleotides during transcription using a DNA strand as a template

Steps in protein production [2]:

- transcription
- translation

Transcription [3]:

- takes place inside the nucleus
- RNA polymerase connects together a chain of bases complementary to those on the DNA
- this makes mRNA

mRNA

messenger RNA

mRNA function:

acts as a template to carry information from the DNA to the ribosome

Translation [4]:

- takes place in the cytoplasm
- mRNA connects to rRNA
- specific tRNA have a complementary anticodon to the codons on mRNA and carry specific amino acids
- tRNA chain together amino acids according to codons

rRNA

ribosomal RNA

rRNA function:

structural component of ribosomes

tRNA

transfer RNA

tRNA function:

carries amino acids to the ribosome according to mRNA codons

Mutation

random error in gene replication that leads to a change

Mutation during mitosis

affects localised cells

Mutation during meiosis

affects entire organism

Non-coding region

segments of DNA which are not directly used for coding protein

Mutagen

chemical or physical agent that causes a mutation

Substitution

one nucleotide replaces another

Substitution effects [2]:

- harmless; no change to amino acid
- change in one amino acid which can affect protein structure

Insertion

addition of bases

Insertion effect:

shifts many codons and changes protein structure

Deletion

removal of bases

Deletion effect:

shifts many codons and changes protein structure

Effects of mutation [3]:

- slight/no effect
- altered protein, resulting in better or worse function
- in non-coding regions: can affect phenotype

Non-coding regions function:

switching genes on and off