DNA, Genes And Chromosomes

Question 1

Shape and structure of mRNA

Answer 1

Straight and single stranded

Question 2

Where is mRNA formed

Answer 2

In the nucleus in eukaryotes as pre-mRNA so splicing remixed introns to form mRNA which leaves via the nuclear pores

Question 3

How is mRNA used for protein synthesis

Answer 3

Associates with ribosomes and acts as a template

Question 4

tRNA structure

Answer 4

Small, single stranded folded into clover leaf shape held by hydrogen bonds

Question 5

What does tRNA have (2)

Answer 5

Amino acid binding site: three bases sticking out which attach to one amino acid

Anticodon: sequence of three bases which pair with mRNA codon

Question 6

Genome

Answer 6

Complete set of genes in an organism

Question 7

Proteome

Answer 7

Full range of proteins that a cell is able to produce

Question 8

Triplet code (codon)

Answer 8

Three bases (triplet) codes for one amino acid

Question 9

Gene

Answer 9

A base sequence of DNA which codes for a particular protein or functional RNA

Question 10

how to describe genes

Answer 10

universal
degenerate
non-overlapping

Question 11

universal code

Answer 11

all organisms have the same triplet codon which code for the same amino acid

Question 12

degenerate

Answer 12

64 combinations of bases but only 22 so some amino acids are coded for by more than one triplet code

Question 13

non-overlapping

Answer 13

each triplet is only read once

Question 14

describe eukaryotic DNA

Answer 14

longer, linear DNA associated with histones proteins to form chromosomes

Question 15

how does most of DNA not code for polypeptides

Answer 15

• Between genes are non-coding sequences used in DNA fingerprinting
• Introns: some triplets within genes do not code for an amino acid e.g. stop start codons mark the beginning and end of polypeptide chain (exons are coding DNA)

Question 16

describe prokaryotic DNA

Answer 16

shorter DNA which form a circle (not chromosomes) and not associated with proteins

Question 17

what is prokaryotic DNA similar to

Answer 17

mitochondrial and chloroplast DNA

Question 18

protein synthesis first stage (6 steps)

Answer 18

Transcription – DNA is used as a template to make mRNA

1. DNA helicase breaks hydrogen bonds, exposing the bases
2. Free complementary nucleotides join to the nucleotides on template strand and RNA polymerase joins the nucleotides together to form pre-mRNA
3. DNA strands re-join behind the building of pre-mRNA
4. Once RNA polymerase detects the stop codon, it detaches, completing production
5. Pre-mRNA is spliced where introns are removed and exons join together to form mRNA
   - Introns prevent synthesis of polypeptide
6. mRNA molecules leave nucleus via nuclear pore and are attracted and attach to ribosomes in the cytoplasm

Question 19

protein synthesis second stage (6 steps)

Answer 19

Translation – mRNA is used to make a protein

7. Ribosome attaches to mRNA molecule in cytoplasm
8. tRNA, carrying an amino acid specific to 3 base anticodon, moves to ribosome and pairs anti-codon sequence with the complementary bases on mRNA
9. Another tRNA molecule with another amino acid will pair with the next codon on mRNA
10. Amino acids join together by peptide bonds to extend polypeptide chain
11. mRNA releases tRNA which releases amino acid
12. tRNA picks up another free amino acid corresponding to its 3 base anti-codon

Question 20

Function of histones

Answer 20

Fixes DNA in position