4 Genetic Information & variation- DNA, genes & chromosomes

Question 1

What is the structure of DNA in a prokaryote?

Answer 1

-Short
-Circular
-Not associated with proteins
-In cytoplasm
-Supercoiled (chromosomes coil around themselves so they can fit inside cell)

Question 2

What is the structure of DNA in a eukaryote?

Answer 2

-Long
-Linear
-Associated with proteins, histones- DNA coils around them, condenses into chromosome
-In nucleus

Question 3

What are homologous chromosome pairs?

Answer 3

Diploid (2 complete sets of chromosomes) eukaryotes have homologous pairs of chromosomes, number of pairs varies for species (23 in humans)
Homologous- chromosome from mother and father have same genes at same loci, but different alleles at loci

Question 4

What is the endosymbiotic theory?

Answer 4

Explains presence of DNA in mitochondria & chloroplasts
States bacterial cells were engulfed by larger cells during evolution
Bacteria and host cell made beneficial symbiotic relationship, bacterial cell incorporates into larger cell, become organelles.
The bacterial cells here are mitochondria and chloroplasts- when they were free-living bacteria, they needed their own DNA to survive (explains why they still have DNA)

Question 5

What is the structure of DNA in mitochondria and chloroplasts?

Answer 5

-Short
-Circular
-Not associated with proteins

Question 6

What is the role of mitochondrial/chloroplast DNA?

Answer 6

Mitochondria- encodes enzymes used in respiration
Chloroplasts- encodes enzymes used in photosynthesis
These enzymes are readily available in organelles

Question 7

What is a gene?

Answer 7

-Section/base sequence of DNA, codes for amino acid sequence of polypeptide or functional RNA (e.g. rRNA,tRNA)
-Each has a specific base sequence (A, T, C, G)

Question 8

What is the locus?

Answer 8

Specific location of a gene in DNA, a fixed position

Question 9

What are codons/ triplets?

Answer 9

-Three bases in a gene
-Specific codon/triplet encodes specific amino acid
-Sequence of codons are translated into a sequence of amino acids
-Together the amino acids form a polypeptide

Question 10

How is the sequence of bases in a gene made into a polypeptide?

Answer 10

Copying DNA into messenger RNA (mRNA), which is then copied into a corresponding polypeptide

Question 11

What else do genes encode? (other than polypeptide)

Answer 11

Functional RNA molecule, necessary for protein synthesis

Question 12

What are non-coding genes?

Answer 12

A large proportion of genes in eukaryotic DNA doesn’t code for any polypeptide, have no biological function

Question 13

What are exons?

Answer 13

Coding regions in a gene, sequences are interrupted at regular intervals by non-coding regions

Question 14

What are introns?

Answer 14

Non-coding regions in a gene (When genes are translated for protein synthesis, introns are removed from sequence)

Question 15

What are multiple repeats?

Answer 15

Random sequences in DNA that will be repeated many times (e.g. CGCCGCCGC)
Regions of non-coding multiple repeats in eukaryotic DNA

Question 16

What is the genetic code?

Answer 16

The combination of triplet codes in the genome

Question 17

Which 3 features describe the genetic code?

Answer 17

Non-overlapping, degenerate and universal

Question 18

What does non-overlapping mean?

Answer 18

There is no overlap between triplet codes, each is separate from other triplets in chromosomes

Question 19

What does degenerate mean?

Answer 19

Some amino acids are encoded by more than one codon (e.g. tyrosine is encoded by TAC and TAT) There are 64 possible triplet codes, only 20 amino acids

Question 20

What does universal mean?

Answer 20

The same 4 bases are used in the DNA of every organism
Same codons encode same amino acids in every organism and transcribed into mRNA and translated into amino acids in every organism