Unit 4 - Genetics

AQA GCE A-Level Biology - Unit 4 - Genetics

[3.4.1] What type of DNA is present in mitochondria and chloroplasts?

Circular DNA.

[3.4.1] How did mitochondria and chloroplasts become present inside cells?

Endosymbiosis.

[3.4.1] What type of DNA is present in mitochondria and chloroplasts?

Circular DNA.

[3.4.1] How did mitochondria and chloroplasts become present inside cells?

Endosymbiosis.

[3.4.1] What is a gene?

A base sequence of DNA that codes for a specific sequence of amino acids, they occupy a fixed position (locus) on a chromosome.

[3.4.1] What is a homologous pair?

A pair of chromosomes with the same type of gene at the same locus.

[3.4.1] What is an allele?

Another form of the same gene.

[3.4.1] How do different alleles impact the tertiary structure of a protein?

Different alleles have slightly different base sequences of DNA - they are likely to produce different polypeptides because the sequence of bases on DNA determines the sequence of amino acids for the protein. This impacts the tertiary structure of the protein because bonds form in different places.

[3.4.1] How can different alleles impact our phenotype?

A different base sequence may produce a non-functioning enzyme. Enzymes control the speed of the metabolic pathways in our bodies which affect our growth and contribute to our development, which ultimately affects our phenotype.

[3.4.1] What is the triplet code?

Each amino acid is coded for by 3 bases.

[3.4.1] What is meant by the code being degenerate?

Some amino acids are coded for by more than one codon.

[3.4.1] What is meant by the code being non-overlapping?

Each base is only read once.

[3.4.1] What is meant by the code being universal?

The same triplet code always codes for the same amino acid in an organism.

[3.4.1] What are introns?

Non-coding sections of a gene.

[3.4.1] What are exons?

Coding sections of a gene.

[3.4.2] What is the genome?

The complete sets of genes within a cell.

[3.4.2] What is the proteome?

The full range of proteins that a cell is able to produce.

[3.4.2] What is mRNA?

mRNA is made of single long strands of RNA, which has been transcribed from DNA in the nucleus and passed into the cytoplasm for protein synthesis.

[3.4.2] What are the properties of mRNA?

• mRNA is single stranded (linear) to ensure that it is small enough to pass through the nuclear pores.

• mRNA is short (only made of a few nucleotides) to further ensure that it is small enough to pass through the nuclear pores.

• mRNA has complimentary base pairing with DNA so it can accurately copy the DNA sequence. 

[3.4.2] What is tRNA?

tRNA is made of single strands of RNA arranged in a “cloverleaf” shape, it brings amino acids to the ribosomes for protein synthesis.

[3.4.2] What are the properties of tRNA?

tRNA has a cloverleaf shape held together by hydrogen bonds to enable stability.

tRNA has a specific amino acid binding site to enable transport of amino acids to the ribosome.

tRNA has an anticodon which will bind to a specific mRNA codon to ensure that the amino acid is inserted into the correct position.

[3.4.2] Which organelles are involved in the production of proteins?

• Nucleus contains DNA which codes for proteins.

• Ribosome produces coded protein via protein synthesis.

• Rough Endoplasmic Reticulum transports it to the golgi apparatus.

• Golgi apparatus packages and modifies it with carbohydrates and lipids.

• Golgi vesicles secretes the protein out of the cell.

[3.4.2] What is transcription?

Complementary mRNA is coded for by a specific region of DNA. The DNA unwinds (catalysed by the enzyme DNA helicase), involving the breaking of hydrogen bonds between base pairs.
The coding strand acts as a template by attracting complementary RNA nucleotides. Guanine binds to cytosine and uracil binds with adenine and therefore the pre-mRNA molecule is assembled.

[3.4.2] What is pre-mRNA?

Pre-mRNA includes both exons and introns - the introns are removed in a process called splicing.

[3.4.2] What is splicing?

Ribonucleoprotein molecules are needed to bind to the pre-mRNA intron. The molecules bind to the intron and cause it to make a loop. The intron then detaches and the splice sites join together. 

[3.4.3] What is a diploid cell?

Each cell contains two of each chromosome.

[3.4.3] What is a haploid cell?

Each cell contains half of the normal number of chromosomes.

[3.4.3] What is fertilisation?

A haploid sperm cell fuses with a haploid egg cell, making a diploid zygote.

• During sexual reproduction, any sperm can fertilise any egg — fertilisation is random. Random fertilisation produces zygotes with different combinations of chromosomes from both parents. This mixing of genetic material increases genetic diversity within a species.

[3.4.3] What is meiosis?

The process of producing gametes; diploid cells divide by meiosis to produce genetically unique haploid daughter cells.

[3.4.3] What is the process of meiosis?