4 - Nucleus, DNA, RNA and chromosomes

Question 1

Nuclear Membrane properties

Answer 1

• Double lipid bilayer
• Semipermeable membrane with nuclear pores
• Outer membrane is continuous w/ ER
• Encloses nucleoplasm
• Breaks down and reforms during cell division
• Regulates flow in and out of nucleus

Question 2

Describe nuclear pores

Answer 2

• Located in nucleus membrane and regulate entry/exit from nucleus
• ## Selective entry and exit of proteins and RNA plays a role in regulating gene expression

Question 3

Describe the nucleus

Answer 3

• Contains nucleolus (produces ribosomes, which make proteins)
• Has chromosomes (genes)
• Nucleoplasm: liquid in nucleus

Question 4

Describe DNA

Answer 4

• Found in living organisms
• Stores all genetic material inherited from parents
• Provides code for synthesis of other molecules

Question 5

Describe RNA

Answer 5

• Function: carry out instructions coded in DNA
• 3 types:
• Messenger RNA (mRNA): carries info for protein synthesis from DNA molecules in nucleus to ribosomes
• Ribosomal RNA (rRNA): structural component of ribosomes (protein synthesis)
• Transfer RNA (tRNA): transfers a.a to ribosome. A.a used to assemble a new polypeptide chain

Question 6

What is the structure of nucleic acid?

Answer 6

1. Pentose sugar (deoxyribose/ribose): structural backbone
2. Phosphate group: structural backbone
3. Nitrogenous base: contains info that tells cells what to make

Question 7

What are purines and pyramidines

Answer 7

Purines: 2 aromatic rings in their structure
Pyramidines: 1 aromatic ring

Question 8

What bases bind together?

Answer 8

A (purine) - T (pyramidine)
G (purine) - C (pyramidine)

Question 9

Describe the formation of DNA

Answer 9

• Pentose sugar of 1 nucleotide forms covalent bond with phosphate of another
• Creates the sugar-phosphate backbone
• Runs 5’ to 3’

Question 10

How are 2 strands connected?

Answer 10

• Connected in the middle by nitrogenous bases
• Allows for the creation of double helix
• Run antiparallel to each other

Question 11

What are the major and minor grooves?

Answer 11

• 1 major and 1 minor groove per turn
• DNA-protein contacts occur in major groove

Question 12

Describe what genes are

Answer 12

• Segments of DNA that contain hereditary info
• Vary in size (different amounts of base pairs)

Question 13

What is the genome?

Answer 13

• Entire set of DNA instructions found in a cell
• Has all the info for someone to develop and function
• Protein coding is only 2% of the genome (20-21,000 genes)

Question 14

Where are genes located

Answer 14

• DNA polymers in nucleus (most genes)
• In DNA in mitochondria (37 genes)

Question 15

Why is DNA packaged into chromosomes?

Answer 15

Too long
Prevents damage to it

Question 16

How is DNA packaged into chromosomes?

Answer 16

1. Double stranded DNA
2. Formation of nucleosome (histone proteins, non histone proteins and DNA)
3. Nucleosomes condense and form chromatin (30nm)
4. Fibres loop and condense further (looped domains)
5. Loops coil to form condensed metaphase chromosomes

Question 17

Describe chromosomes

Answer 17

• Contains 1 double stranded DNA before replication
• 2 sister chromatids join together at centromere
• Have long arm and short arm

Question 18

Describe diploid/haploid

Answer 18

diploid: 2 complete homologous pairs of chromosomes
Haploid: 1 chromosome (sex chromosome)

Question 19

Describe homologous pairs

Answer 19

• Same size and shape (not sex chromosomes)
• Same genes in same location
• Doesn’t have to have the same versions of genes (since genetic material comes from different parents)

Question 20

How many chromosomes do humans have?

Answer 20

• 46 chromosomes (23 pairs)
• 22 pairs: autosomes
• 1 set of sex chromosomes (XX or XY)
• Can have other variations (intersex)

Question 21

How do offspring inherit genes

Answer 21

• 1 chromosome from each parent
• Begins with union of gametes (sperm and egg)
• Fertilised egg - zygote (diploid)
• As human develops into mature adult, mitosis of zygote and its descendant cells generates all somatic cells of the body

Question 22

Define character

Answer 22

Heritable feature that varies among individuals (e.g: hair colour)

Question 23

Define trait

Answer 23

Each variant for a character (e.g: blonde/brown hair)

Question 24

Define somatic cell

Answer 24

Cells that aren’t egg or sperm

Question 25

Describe mendelian inheritance

Answer 25

• Inheritance of traits controlled by a single gene
• Alleles from each parent may be more dominant/recessive

Question 26

How do patterns of inheritance depend on location of genes

Answer 26

• Autosomal traits are controled by genes on one of the 22 pairs of human autosomes
• Sex linked traits are controlled by genes on the sex chromosome
• Most are controlled by genes on X chromosome bc Y is small
• Single-gene X-linked traits have a different pattern of inheritance. Passed down the maternal line

Question 27

2 tools to study inheritance patterns

Answer 27

• Pedigree chart: shows how a trait is passed from generations within a family
• Punnett Square: allows you to determine the expected ratios of possible genotypes in offspring of 2 parents

Question 28

Describe human x-linked mendelian traits

Answer 28

• Recessive x-linked traits show a different pattern of inheritance than autosomal traits
• If only 1 X chromosome (XY or XO), then there is only 1 allele for any x-linked trait (recessive x-linked allele is always expressed)
• If there are 2 X chromosomes (XX or XXY) then the person has 2 alelles for any x-linked trait chromosomes (must inherit 2 copies of recessive allele to express an x-linked recessive trait

Question 29

What are prokaryotes? How are they divided? Where is their DNA?

Answer 29

• Small, single-celled organisms whose cells lack a nucleus and other organelles
• Divided into bacteria and archaea
• Don’t have inner membranes, so their genome is in the nucleoid (region of the cytoplasm)