4.1 GENES AND CHROMOSOMES

WHY MUST DNA STAY IN THE NUCLEUS?

To stay away from chemical reactions.

WHAT DOES DNA CARRY?

The genetic code to allow the cell to make proteins.

WHAT ARE THE TWO ONLY DIFFERENCES BETWEEN DNA STRANDS?

1. Length.

2. Sequence of bases.

EXON

Base sequence coding for polypeptide

/ sequence of amino acids.

HOW MANY BASES ARE NEEDED TO CODE FOR AN AMINO ACID?

Three.

WHAT ARE THREE FEATURES OF THE GENETIC CODE?

1. The code is non-overlapping - each base would be a part of 3 triplets.

2. The code is degenerate - most amino acids are coded for by multiple triplets.

3. The code is universal - a given triplet will produce the same amino acid in all organisms.

HOW DO GENES CODE FOR PROTEINS?

They code for RNA

Base/nucleotide sequence

(In) triplets

(Determines) sequence of amino acid in polypeptide.

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HOW IS mMRNA formed?

WHAT IS IT COMPLEMENTARY TO?

By the transcription of a gene in DNA in the nucleus.

Complementary to the DNA in its base sequence.

WHY AND WHERE IS mRNA EASILY BROKEN DOWN?

It has unpaired bases, so it is easily broken down in the cytoplasm.

It only needs to exist temporarily until the protein is manufactured.

HOW BIG IS tNRA?

WHAT IS IT?

• Relatively small.

• Around 80 nucleotides.

• It is a single strand which folds back on itself.

WHICH BOND IS PRESENT IN A tRNA MOLECULE AND WHAT IS ITS PURPOSE?

WHAT DOES ONE END OF THE CHAIN ATTACH TO?

• Hydrogen: Forms within complementary sections of the molecule - stabilises molecule.

• One end of the chain attaches to an amino acid.

WHAT IS THE DIFFERENCE BETWEEN EACH TYPE OF tRNA?

WHAT IS AT THE BASE IF EVERY tRNA?

Each is able to carry a single specific amino acid.

Base has a sequence of three bases, known as the anticodon.

For each amino acid carried, there is a different sequence of bases on the anticodon.

CAN RNA LINK WITH DNA AND OTHER RNA?

Yes.

DEFINE ‘NON-CODING BASE SEQUENCES AND DESCRIVE WHERE THE NON CODING MULTIPLE REPEATS ARE POSITIONED IN THE GENOME? (2)

1. DNA that does not code for protein_/polypeptides / sequence of a.a / tRNA_/rRNA

2. (Positioned) between genes;

_{Reject (positioned) ‘in introns’ or ‘between exons’.}

_{Accept ‘(Positioned) at the end of chromosomes’ or ‘(Positioned) in the telomeres’.}

CHLOROPLAST VS NUCLEUS DNA?

In chloroplasts:

1. DNA shorter

2. Fewer genes;

3. DNA circular not linear; Accept DNA in a loop not linear Accept no chromosomes (in chloroplast) unlike nucleus

4. Not associated with protein/histones, unlike nuclear DNA;

5. Introns absent but present in nuclear DNA.

NAME THE STRUCTURES LABELLED

W = amino acid binding site and X = anticodon; W Idea of binding site needed

EUKARYOTIC VS PROKARYOTIC DNA:

S - Nucleotide structure is identical.

S - Nucleotides joined by phosphodiester bond.

S - DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes.

D - Eukaryotic DNA is longer.

D - Eukaryotic DNA contain introns.

D - Eukaryotic DNA is linear, prokaryotic DNA is circular;

D - Eukaryotic DNA is associated with histones.

D - Eukaryotic DNA no plasmids, prok yes.

HOW CAN CHROMOSOMES DIFFER ALONG THEIR LENGTHS?

Differences in base sequences

Differences in histones/interaction with histones

Differences in condensation/(super)coiling;